V.U. Mme Cl. Stiévenart ISSN - 0250 -5010 Av. Armand Huysmans 206, bte 10 B- 1050 Bruxelles - Brussel

ANNALEN VAN DE BELGISCHE VERENIGING VOOR STRALINGSBESCHERMING

VOL. 30, N°4, 2005 1er trim. 2006

Driemaandelijkse periodiek Périodique trimestriel 1050 Brussel 5 1050 Bruxelles 5

ANNALES DE L’ASSOCIATION BELGE DE RADIOPROTECTION

radio vol30 n4V2.indd 1 3/04/06 16:42:18 ii iii

SOMMAIRE INHOUD

Le projet de nouvelles recommandations de la CIPR: Les raisons d’un changement Annie SUGIER, Jean-Claude NENOT, Jean-François LECOMTE p. 187

The in vivo measurements of radioactive body burdens J.L. GENICOT p.

Hoofdredacteur Mr C. Steinkuhler Rédacteur en chef Rue de la Station 39 B- 1325 Longueville

Redactiesecretariaat Mme Cl. Stiévenart Secrétaire de Rédaction Av. Armand Huysmans 206, bte 10 B- 1050 Bruxelles - Brussel

Publikatie van teksten in de Annalen Les textes publiés dans les Annales gebeurt onder volledige le sont sous l’entière responsabilité verantwoordelijkheid van de auteurs. des auteurs. Nadruk, zelfs gedeeltelijk uit deze Toute reproduction, même partielle, teksten, mag enkel met schriftelijke ne se fera qu’avec l’autorisation toestemming van de auteurs en van écrite des auteurs et de la de Redactie. Rédaction.

radio vol30 n4V2.indd 2 3/04/06 16:42:18 ii iii

SOMMAIRE INHOUD

Le projet de nouvelles recommandations de la CIPR: Les raisons d’un changement Annie SUGIER, Jean-Claude NENOT, Jean-François LECOMTE p. 187

The in vivo measurements of radioactive body burdens J.L. GENICOT p.211

Hoofdredacteur Mr C. Steinkuhler Rédacteur en chef Rue de la Station 39 B- 1325 Longueville

Redactiesecretariaat Mme Cl. Stiévenart Secrétaire de Rédaction Av. Armand Huysmans 206, bte 10 B- 1050 Bruxelles - Brussel

Publikatie van teksten in de Annalen Les textes publiés dans les Annales gebeurt onder volledige le sont sous l’entière responsabilité verantwoordelijkheid van de auteurs. des auteurs. Nadruk, zelfs gedeeltelijk uit deze Toute reproduction, même partielle, teksten, mag enkel met schriftelijke ne se fera qu’avec l’autorisation toestemming van de auteurs en van écrite des auteurs et de la de Redactie. Rédaction.

radio vol30 n4V2.indd 3 3/04/06 16:42:18 iv

Annales de l’Association Belge de Radioprotection, Vol.30, n°4, 2005

LE PROJET DE NOUVELLES RECOMMANDATIONS DE LA CIPR : LES RAISONS D’UN CHANGEMENT *

Annie Sugier, Jean-Claude Nénot, Jean-François Lecomte

Institut de Radioprotection et de Sûreté Nucléaire

* paru dans Radioprotection, Volume 40, N°3, 2005 Reproduit avec l’autorisation de l’éditeur.

Résumé Depuis sa création en 1928, la Commission Internationale de Protection Radiologique (CIPR) produit régulièrement des recommandations sur la protection contre les rayonnements ionisants ; ces recommandations sont habituellement reprises par les organisations internationales et par les Etats. Depuis 1990, date des recommandations les plus récentes (Publication 60), la progression des connaissances scientifiques, les développements techniques, le retour d’expérience et le souci d’adhérer à l’évolution de la société, ont incité la CIPR à modifier en profondeur son système de protection. Le tout dernier projet de recommandations, récemment rendu public pour consultation et appel de propositions, est décrit et discuté.

Mots-clés : Recommandations / CIPR / radioprotection / contraintes

radio vol30 n4V2.indd 4 3/04/06 16:42:19 iv

Annales de l’Association Belge de Radioprotection, Vol.30, n°4, 2005

LE PROJET DE NOUVELLES RECOMMANDATIONS DE LA CIPR : LES RAISONS D’UN CHANGEMENT *

Annie Sugier, Jean-Claude Nénot, Jean-François Lecomte

Institut de Radioprotection et de Sûreté Nucléaire

* paru dans Radioprotection, Volume 40, N°3, 2005 Reproduit avec l’autorisation de l’éditeur.

Résumé 187 Depuis sa création en 1928, la Commission Internationale de Protection Radiologique (CIPR) produit régulièrement des recommandations sur la protection contre les rayonnements ionisants ; ces recommandations sont habituellement reprises par les organisations internationales et par les Etats. Depuis 1990, date des recommandations les plus récentes (Publication 60), la progression des connaissances scientifiques, les développements techniques, le retour d’expérience et le souci d’adhérer à l’évolution de la société, ont incité la CIPR à modifier en profondeur son système de protection. Le tout dernier projet de recommandations, récemment rendu public pour consultation et appel de propositions, est décrit et discuté.

Mots-clés : Recommandations / CIPR / radioprotection / contraintes

radio vol30 n4V2.indd 187 3/04/06 16:42:19 Le présent article a pour objectif de situer le projet de nouvelles qui concerne l’exposition interne, alors que dans la catégorie explicative, recommandations de la Commission Internationale de Protection la Publication 91 (1963) jette les bases de la doctrine actuelle, en discutant Radiologique (CIPR) dans le cadre de l’évolution de ses travaux et de de l’acceptabilité du risque, puisque que les expositions « habituelles » mettre en évidence, à un moment important du processus de consultation ne sont pas exemptes de tout risque. A cette époque, la CIPR s’intéresse qu’elle a engagé, les principales caractéristiques de ce texte. S’agissant de très près aux cancers radio-induits et aux effets héréditaires, risques d’un processus en cours, il faut s’attendre à des modifications du texte dans potentiels des faibles doses donc des situations normales ; en revanche, les mois à venir, notamment dans la présentation du tableau des contraintes elle délaisse les effets des fortes doses, qui ne peuvent résulter que de de dose. situations accidentelles. Le principe d’optimisation de la protection apparaît clairement pour la première fois : maintenir toutes les doses aux valeurs les plus faibles auxquelles l’on peut parvenir sans difficulté, LES BASES HISTORIQUES DE LA DOCTRINE compte tenu des aspects sociaux et économiques (couramment représenté par l’acronyme anglais ALARA : as low as readily achievable) et la limite La CIPR a été créée en1928, quand les radiologues prennent conscience annuelle est fixée à 50 mSv pour les travailleurs et à 5 mSv pour les des lésions causées par les rayons X et par le radium à leurs patients et à personnes du public. L’optimisation de la protection occupe une place de eux-mêmes. La première limite de dose, qui date de 1938, concernait les plus en plus importante ; un chapitre entier de la Publication 222 (1973) seuls professionnels et équivalait à environ 500 millisieverts (mSv) par an. lui est consacré. 188 Ce système de protection était censé garantir l’absence totale de risque, puisqu’il protégeait contre les effets des fortes doses de rayonnements, les En 1977 la Publication 26 effectue la synthèse des recommandations seuls connus à cette époque. Après la seconde guerre mondiale, l’action précédentes, tout en tenant compte de l’actualisation des connaissances. cancérogène des rayonnements a été reconnue et il est devenu évident Elle définit les trois principes de base qui régiront la protection que des expositions inférieures aux limites pouvaient causer des effets radiologique pendant plus de vingt ans : extrêmement graves. La CIPR recommande alors un abaissement des • la justification des pratiques, limites de dose : 3 mSv par semaine pour les travailleurs (soit environ • l’optimisation de la protection, en reprenant les termes 150 mSv par an) et le dixième de cette valeur pour la population en raison « ALARA », de possibles risques génétiques et de la sensibilité de certains individus • la limitation des doses. qui les rend particulièrement vulnérables aux rayonnements. La première publication officielle, identifiée comme la Publication 1, date de 1959 ; la limite professionnelle hebdomadaire laisse la place à une limite annuelle qui tient compte de l’accumulation des doses ; cette limite correspond à une moyenne de 50 mSv par an mais autorise des dépassements exceptionnels, bornés à 30 mSv par trimestre, soit un maximum de 120 mSv par an. Les publications suivantes sont techniques et explicatives. Dans la catégorie technique, la Publication 2 de 1960 constitue un document de base pour ce

radio vol30 n4V2.indd 188 3/04/06 16:42:20 Le présent article a pour objectif de situer le projet de nouvelles qui concerne l’exposition interne, alors que dans la catégorie explicative, recommandations de la Commission Internationale de Protection la Publication 91 (1963) jette les bases de la doctrine actuelle, en discutant Radiologique (CIPR) dans le cadre de l’évolution de ses travaux et de de l’acceptabilité du risque, puisque que les expositions « habituelles » mettre en évidence, à un moment important du processus de consultation ne sont pas exemptes de tout risque. A cette époque, la CIPR s’intéresse qu’elle a engagé, les principales caractéristiques de ce texte. S’agissant de très près aux cancers radio-induits et aux effets héréditaires, risques d’un processus en cours, il faut s’attendre à des modifications du texte dans potentiels des faibles doses donc des situations normales ; en revanche, les mois à venir, notamment dans la présentation du tableau des contraintes elle délaisse les effets des fortes doses, qui ne peuvent résulter que de de dose. situations accidentelles. Le principe d’optimisation de la protection apparaît clairement pour la première fois : maintenir toutes les doses aux valeurs les plus faibles auxquelles l’on peut parvenir sans difficulté, LES BASES HISTORIQUES DE LA DOCTRINE compte tenu des aspects sociaux et économiques (couramment représenté par l’acronyme anglais ALARA : as low as readily achievable) et la limite La CIPR a été créée en1928, quand les radiologues prennent conscience annuelle est fixée à 50 mSv pour les travailleurs et à 5 mSv pour les des lésions causées par les rayons X et par le radium à leurs patients et à personnes du public. L’optimisation de la protection occupe une place de eux-mêmes. La première limite de dose, qui date de 1938, concernait les plus en plus importante ; un chapitre entier de la Publication 222 (1973) seuls professionnels et équivalait à environ 500 millisieverts (mSv) par an. lui est consacré. Ce système de protection était censé garantir l’absence totale de risque, 189 puisqu’il protégeait contre les effets des fortes doses de rayonnements, les En 1977 la Publication 26 effectue la synthèse des recommandations seuls connus à cette époque. Après la seconde guerre mondiale, l’action précédentes, tout en tenant compte de l’actualisation des connaissances. cancérogène des rayonnements a été reconnue et il est devenu évident Elle définit les trois principes de base qui régiront la protection que des expositions inférieures aux limites pouvaient causer des effets radiologique pendant plus de vingt ans : extrêmement graves. La CIPR recommande alors un abaissement des • la justification des pratiques, limites de dose : 3 mSv par semaine pour les travailleurs (soit environ • l’optimisation de la protection, en reprenant les termes 150 mSv par an) et le dixième de cette valeur pour la population en raison « ALARA », de possibles risques génétiques et de la sensibilité de certains individus • la limitation des doses. qui les rend particulièrement vulnérables aux rayonnements. La première publication officielle, identifiée comme la Publication 1, date de 1959 ; la limite professionnelle hebdomadaire laisse la place à une limite annuelle qui tient compte de l’accumulation des doses ; cette limite correspond à une 1 Recommandations de la Commission Internationale de Protection Radiologique, Publication CIPR 9 (traduction), moyenne de 50 mSv par an mais autorise des dépassements exceptionnels, 1963. paragraphe 52. Ed. : Service Central de Documentation, CEN-Saclay. bornés à 30 mSv par trimestre, soit un maximum de 120 mSv par an. Les 2 Recommandations de la Commission Internationale de Protection Radiologique, Publication CIPR 22 (traduction), 1973, Les implications des recommandations de la Commission de maintenir les doses aux valeurs les plus faibles publications suivantes sont techniques et explicatives. Dans la catégorie qu’il soit possible d’atteindre sans difficulté. Chapitre B : Application pratique du paragraphe 52 de la Publication 9, paragraphes 12 à 19. technique, la Publication 2 de 1960 constitue un document de base pour ce 3 La philosophie utilitariste a été fondée au 17e siècle par Jeremy Bentham, puis répandue au siècle dernier dans les pays anglo-saxons. Contrairement à ce que le mot semble suggérer en français, cette philosophie ne glorifie pas l’égocentrisme, mais constitue une doctrine altruiste. Son principe général peut s’énoncer : une action est bonne quand elle tend à réaliser le plus grand bien possible au plus grand nombre de personnes concernées ; dans le cas contraire, elle est mauvaise. De façon générale, les utilitaristes considèrent les conséquences économiques bénéfiques qui se rapportent aux différents risques. Ils s’opposent aux tenants de l’éthique contractuelle, qui placent au premier rang le droit à la protection individuelle contre les risques réels ou potentiels.

radio vol30 n4V2.indd 189 3/04/06 16:42:20 La doctrine de la Publication 26 repose sur une éthique de protection de Les trois principes de base sont conservés, mais l’accent est mis la collectivité, de type utilitariste ; cette approche considère que, si la sur l’optimisation de la protection, qui constitue le fer de lance du protection de la société est assurée, celle de l’individu est aussi assurée de système. L’optimisation s’appuie sur la contrainte, qui se différencie de façon satisfaisante3. Le système repose sur l’analyse coût-bénéfice, avec la limite, car elle s’applique à une source donnée de rayonnements mais comme outils la dose collective, qui est considérée comme une mesure est liée à l’individu exposé. La contrainte représente donc une fraction adéquate du risque global en rapport avec une source de rayonnements. de la limite et constitue une aide à l’exploitant qui doit l’utiliser de façon La limite annuelle de dose qui garantit la protection individuelle figure au prospective ; en revanche ce n’est ni une limite supplémentaire ni un deuxième plan et ne constitue qu’un garde-fou. Elle est maintenue à 50 niveau d’intervention ou d’investigation. Le système repose toujours sur mSv pour les travailleurs et à 5 mSv pour la population, dans la mesure où l’acceptabilité d’un certain niveau de risque, puisque la CIPR considère la moyenne sur la vie ne dépasse pas 1 mSv par an. La comparaison des qu’une relation dose-effet linéaire sans seuil constitue la représentation la risques liés à ces doses avec ceux de la vie courante permet de juger de leur plus crédible de l’induction des cancers radio-induits. Pour juger de cette acceptabilité : le niveau de risque est comparable, pour les travailleurs à acceptabilité, la CIPR abandonne la comparaison avec d’autres risques, celui des professions les plus sûres, et pour les personnes du public à celui qui le plus souvent n’étaient pas comparables entre eux, en raison de leur de la vie de tous les jours. Cette publication évoque en outre la protection nature (par exemple, il est difficile de donner le même poids à un décès de l’environnement : il est probable que le niveau de sécurité nécessaire aléatoire par cancer survenu quelques dizaines d’années après l’exposition pour assurer la protection de tous les individus du genre humain convient et à une mort accidentelle) et juge de l’acceptabilité du risque radio-induit 190 également pour protéger les autres espèces, sinon nécessairement tous les de façon absolue. Ainsi, en se basant sur un risque de cancer mortel de 4% individus de ces espèces4. par sievert pour les travailleurs (toute personne âgée de 18 à 65 ans) et de 5% par sievert pour la population (tous âges confondus), la CIPR juge que le maximum tolérable sur la vie entière est 1 sievert pour les travailleurs LA SYNTHESE DE LA DOCTRINE EN 1990 et 70 mSv pour les personnes du public. Les limites de dose annuelles en sont déduites : abaissées à 20 mSv pour les premiers (avec dépassement Dans les années 80 les connaissances sur le risque d’effets stochastiques autorisé jusqu’à 50 mSv une année, dans la mesure ou la moyenne sur s’affinent ; le risque de cancer radio-induit s’avère sous-évalué et justifie 5 ans ne dépasse pas 20 mSv par an) et maintenues à 1 mSv5 pour les un abaissement des limites. La CIPR entreprend alors un travail de seconds. Les limites continuent de jouer le rôle d’une garantie individuelle synthèse et de refonte afin d’obtenir un système logique et cohérent, donc qui agît comme correctif ou butoir au libre jeu de l’optimisation. d’usage pratique. Ce système est conçu pour garantir une protection de haut niveau à tous les individus dans toutes les circonstances et éviter Pour répondre au mieux au souci de logique et de cohérence de l’ensemble de tout manquement à l’équité. C’est le premier pas vers un recentrage sur ses recommandations, la CIPR fait la distinction entre (i) les activités humaines l’individu. La Publication 60 précise d’emblée son objectif 4 : donnant lieu à des expositions : les pratiques qui ajoutent des doses et les procurer à l’homme un niveau de protection approprié, interventions qui en retranchent, (ii) les types d’exposition : professionnelle, sans limiter indûment les activités bénéfiques à l’origine publique et médicale, et (iii) les expositions réelles et les expositions potentielles. des expositions. Pour l’application de ses recommandations, elle définit de nombreux niveaux

4 Recommandations 1990 de la Commission Internationale de Protection Radiologique, Publication 60, (traduction), 1991, Pergamon Press, paragraphe 15.

radio vol30 n4V2.indd 190 3/04/06 16:42:21 La doctrine de la Publication 26 repose sur une éthique de protection de Les trois principes de base sont conservés, mais l’accent est mis la collectivité, de type utilitariste ; cette approche considère que, si la sur l’optimisation de la protection, qui constitue le fer de lance du protection de la société est assurée, celle de l’individu est aussi assurée de système. L’optimisation s’appuie sur la contrainte, qui se différencie de façon satisfaisante3. Le système repose sur l’analyse coût-bénéfice, avec la limite, car elle s’applique à une source donnée de rayonnements mais comme outils la dose collective, qui est considérée comme une mesure est liée à l’individu exposé. La contrainte représente donc une fraction adéquate du risque global en rapport avec une source de rayonnements. de la limite et constitue une aide à l’exploitant qui doit l’utiliser de façon La limite annuelle de dose qui garantit la protection individuelle figure au prospective ; en revanche ce n’est ni une limite supplémentaire ni un deuxième plan et ne constitue qu’un garde-fou. Elle est maintenue à 50 niveau d’intervention ou d’investigation. Le système repose toujours sur mSv pour les travailleurs et à 5 mSv pour la population, dans la mesure où l’acceptabilité d’un certain niveau de risque, puisque la CIPR considère la moyenne sur la vie ne dépasse pas 1 mSv par an. La comparaison des qu’une relation dose-effet linéaire sans seuil constitue la représentation la risques liés à ces doses avec ceux de la vie courante permet de juger de leur plus crédible de l’induction des cancers radio-induits. Pour juger de cette acceptabilité : le niveau de risque est comparable, pour les travailleurs à acceptabilité, la CIPR abandonne la comparaison avec d’autres risques, celui des professions les plus sûres, et pour les personnes du public à celui qui le plus souvent n’étaient pas comparables entre eux, en raison de leur de la vie de tous les jours. Cette publication évoque en outre la protection nature (par exemple, il est difficile de donner le même poids à un décès de l’environnement : il est probable que le niveau de sécurité nécessaire aléatoire par cancer survenu quelques dizaines d’années après l’exposition pour assurer la protection de tous les individus du genre humain convient et à une mort accidentelle) et juge de l’acceptabilité du risque radio-induit également pour protéger les autres espèces, sinon nécessairement tous les de façon absolue. Ainsi, en se basant sur un risque de cancer mortel de 4% 191 individus de ces espèces4. par sievert pour les travailleurs (toute personne âgée de 18 à 65 ans) et de 5% par sievert pour la population (tous âges confondus), la CIPR juge que le maximum tolérable sur la vie entière est 1 sievert pour les travailleurs LA SYNTHESE DE LA DOCTRINE EN 1990 et 70 mSv pour les personnes du public. Les limites de dose annuelles en sont déduites : abaissées à 20 mSv pour les premiers (avec dépassement Dans les années 80 les connaissances sur le risque d’effets stochastiques autorisé jusqu’à 50 mSv une année, dans la mesure ou la moyenne sur s’affinent ; le risque de cancer radio-induit s’avère sous-évalué et justifie 5 ans ne dépasse pas 20 mSv par an) et maintenues à 1 mSv5 pour les un abaissement des limites. La CIPR entreprend alors un travail de seconds. Les limites continuent de jouer le rôle d’une garantie individuelle synthèse et de refonte afin d’obtenir un système logique et cohérent, donc qui agît comme correctif ou butoir au libre jeu de l’optimisation. d’usage pratique. Ce système est conçu pour garantir une protection de haut niveau à tous les individus dans toutes les circonstances et éviter Pour répondre au mieux au souci de logique et de cohérence de l’ensemble de tout manquement à l’équité. C’est le premier pas vers un recentrage sur ses recommandations, la CIPR fait la distinction entre (i) les activités humaines l’individu. La Publication 60 précise d’emblée son objectif 4 : donnant lieu à des expositions : les pratiques qui ajoutent des doses et les procurer à l’homme un niveau de protection approprié, interventions qui en retranchent, (ii) les types d’exposition : professionnelle, sans limiter indûment les activités bénéfiques à l’origine publique et médicale, et (iii) les expositions réelles et les expositions potentielles. des expositions. Pour l’application de ses recommandations, elle définit de nombreux niveaux

5 Un débat très vif a eu lieu sur le choix de la valeur de 1 mSv qui en fait était déjà introduite dans les recommandations précédentes de la CIPR, comme indiqué plus haut.

radio vol30 n4V2.indd 191 3/04/06 16:42:22 d’action, chacun ayant sa propre signification selon l’activité humaine et le que le risque de cancer aux faibles doses et faibles débits de dose type d’exposition. Elle établit implicitement une échelle de risque pour la est amoindri par rapport à celui des fortes doses aiguës ; gamme de dose dues aux pratiques courantes, en qualifiant les expositions - l’existence d’un seuil à l’action des rayonnements demeure très d’inacceptables (au-dessus de la limite), de tolérables (au-dessous de la limite improbable, bien qu’il ne puisse pas être formellement écarté dans mais au-dessus de la contrainte), d’acceptable (au-dessous de la contrainte) et certaines circonstances; de négligeable (au-dessous d’une certaine valeur qui n’est pas précisée). - une relation linéaire entre la dose et l’effet constitue la meilleure Le résultat final constitue un ensemble remarquablement bâti, dont les représentation du risque de cancer radio-induit ; briques s’imbriquent de façon harmonieuse. L’inconvénient majeur est - certaines valeurs des facteurs de pondération pour les rayonnements

que le système est difficile à appréhender dans son ensemble et que son (wR), qui permettent d’apprécier la dangerosité de chaque type de application est source de confusion et de complications inutiles. Il n’en rayonnement, doivent être légèrement modifiés ;

reste pas moins qu’après sa transcription dans la législation nationale les - les valeurs des facteurs de pondération pour les tissus (wT), qui milieux industriels et médicaux l’adoptent désormais sans état d’âme et permettent d’apprécier la dangerosité des rayonnements en fonction respectent ses implications. de la sensibilité des organes et des tissus, peuvent être affinées ; - dans la gamme des faibles doses (inférieures à quelques dizaines de mSv), les lésions de l’ADN occupent une position clé dans la POURQUOI CHANGER ? cancérogenèse radio-induite. 192 Dans le milieu des années 90, apparaissent des raisons de modifier le Néanmoins, les incertitudes sur les mécanismes et leurs conséquences, système de protection : (i) des raisons scientifiques, afin de tenir compte particulièrement celles en rapport avec des phénomènes récemment de l’apport des dernières connaissances, notamment dans les domaines décrits, comme la réponse adaptative, l’instabilité génomique et l’effet de la radiobiologie et de l’épidémiologie, (ii) des raisons techniques et de proximité, sont encore trop grandes pour prédire de façon précise pratiques, tirant profit du retour d’expérience et (iii) des raisons sociétales, comment elles sont susceptibles de modifier l’estimation actuelle du afin d’adhérer aux courants de pensée adoptés par la société en matière de risque des faibles doses extrapolé à partir des études épidémiologiques. protection contre les nuisances de tous ordres. Les meilleures estimations du risque, compte tenu de ces restrictions, sont les suivantes : LES RAISONS SCIENTIFIQUES concernent : - risque de cancer mortel (par Sv) : 6,2% pour la population et 4,8% pour les travailleurs ; • Le risque de cancer aux faibles doses, qui est revu à la lumière - risque d’effets héréditaires (par Sv) : 0,2% pour la population et des données récentes de l’épidémiologie, de la radiobiologie et de 0,1% pour les travailleurs. l’expérimentation animale. Les principales conclusions sont les Les valeurs arrondies du détriment total sont de 6,5% pour la population suivantes : et de 4,9% pour les travailleurs, ce qui constitue une légère diminution - il n’existe aucune raison valable de modifier la valeur de 2 par rapport aux valeurs précédentes qui étaient respectivement de 7,3% recommandée en 1990 pour le Facteur d’Efficacité de Doses et de et 5,6% (y-inclus les cancers non mortels). Débits de Dose (FEDDD), qui permet de prendre en compte le fait

radio vol30 n4V2.indd 192 3/04/06 16:42:23 d’action, chacun ayant sa propre signification selon l’activité humaine et le que le risque de cancer aux faibles doses et faibles débits de dose type d’exposition. Elle établit implicitement une échelle de risque pour la est amoindri par rapport à celui des fortes doses aiguës ; gamme de dose dues aux pratiques courantes, en qualifiant les expositions - l’existence d’un seuil à l’action des rayonnements demeure très d’inacceptables (au-dessus de la limite), de tolérables (au-dessous de la limite improbable, bien qu’il ne puisse pas être formellement écarté dans mais au-dessus de la contrainte), d’acceptable (au-dessous de la contrainte) et certaines circonstances; de négligeable (au-dessous d’une certaine valeur qui n’est pas précisée). - une relation linéaire entre la dose et l’effet constitue la meilleure Le résultat final constitue un ensemble remarquablement bâti, dont les représentation du risque de cancer radio-induit ; briques s’imbriquent de façon harmonieuse. L’inconvénient majeur est - certaines valeurs des facteurs de pondération pour les rayonnements que le système est difficile à appréhender dans son ensemble et que son (wR), qui permettent d’apprécier la dangerosité de chaque type de application est source de confusion et de complications inutiles. Il n’en rayonnement, doivent être légèrement modifiés ; reste pas moins qu’après sa transcription dans la législation nationale les - les valeurs des facteurs de pondération pour les tissus (wT), qui milieux industriels et médicaux l’adoptent désormais sans état d’âme et permettent d’apprécier la dangerosité des rayonnements en fonction respectent ses implications. de la sensibilité des organes et des tissus, peuvent être affinées ; - dans la gamme des faibles doses (inférieures à quelques dizaines de mSv), les lésions de l’ADN occupent une position clé dans la POURQUOI CHANGER ? cancérogenèse radio-induite. 193 Dans le milieu des années 90, apparaissent des raisons de modifier le Néanmoins, les incertitudes sur les mécanismes et leurs conséquences, système de protection : (i) des raisons scientifiques, afin de tenir compte particulièrement celles en rapport avec des phénomènes récemment de l’apport des dernières connaissances, notamment dans les domaines décrits, comme la réponse adaptative, l’instabilité génomique et l’effet de la radiobiologie et de l’épidémiologie, (ii) des raisons techniques et de proximité, sont encore trop grandes pour prédire de façon précise pratiques, tirant profit du retour d’expérience et (iii) des raisons sociétales, comment elles sont susceptibles de modifier l’estimation actuelle du afin d’adhérer aux courants de pensée adoptés par la société en matière de risque des faibles doses extrapolé à partir des études épidémiologiques. protection contre les nuisances de tous ordres. Les meilleures estimations du risque, compte tenu de ces restrictions, sont les suivantes : LES RAISONS SCIENTIFIQUES concernent : - risque de cancer mortel (par Sv) : 6,2% pour la population et 4,8% pour les travailleurs ; • Le risque de cancer aux faibles doses, qui est revu à la lumière - risque d’effets héréditaires (par Sv) : 0,2% pour la population et des données récentes de l’épidémiologie, de la radiobiologie et de 0,1% pour les travailleurs. l’expérimentation animale. Les principales conclusions sont les Les valeurs arrondies du détriment total sont de 6,5% pour la population suivantes : et de 4,9% pour les travailleurs, ce qui constitue une légère diminution - il n’existe aucune raison valable de modifier la valeur de 2 par rapport aux valeurs précédentes qui étaient respectivement de 7,3% recommandée en 1990 pour le Facteur d’Efficacité de Doses et de et 5,6% (y-inclus les cancers non mortels). Débits de Dose (FEDDD), qui permet de prendre en compte le fait

radio vol30 n4V2.indd 193 3/04/06 16:42:23 • Le risque de maladies non cancéreuses induites par les rayonnements, il était important de faire le point sur 15 années de résultats de travaux affectant les systèmes cardiovasculaire, pulmonaire et digestif, qui scientifiques. Le débat sur les effets des faibles doses, qui n’a pas perdu est confirmé. L’étude des relations dose-effet montre des incertitudes de son acuité, conduisait certains à vouloir réviser l’estimation du risque et ne permet pas de se prononcer sur l’existence ou non d’un seuil correspondant (à la hausse ou à la baisse). qui, s’il existe, pourrait se situer aux environs de 500 mSv. La CIPR reconnaît l’importance de ce type d’effets, mais, en l’état actuel des LES RAISONS TECHNIQUES ET PRATIQUES proviennent connaissances, est incapable de les inclure dans son estimation du essentiellement du retour d’expérience. L’application des recommandations risque global des faibles doses. de 1990 s’est avérée complexe et un grand nombre de problèmes pratiques a été difficile à résoudre. En fait, les difficultés rencontrées constituent, • Les effets des fortes doses, qui font l’objet d’un réexamen. La question pour la plupart, l’envers de la médaille de recommandations qui visaient de la valeur à attribuer à l’EBR (Efficacité Biologique Relative) de plus la perfection intellectuelle que le pragmatisme. Des exemples de chaque rayonnement en fonction de la dose n’est pas entièrement difficultés ou confusions sont fournis par : (i) la frontière entre pratique et résolue, pas plus que ne l’est la diminution de la nocivité en fonction de intervention, qui n’est pas évidente dans certaines situations durables et/ la diminution du débit de dose (problème des expositions prolongées ou anciennes, (ii) la limite de dose pour le public, fixée à 1 mSv, difficile pouvant résulter en des doses élevées, situées au-dessus des seuils des à comprendre lorsqu’elle est comparée au bruit de fond naturel, aux effets déterministes causés par des expositions aiguës). différents niveaux d’intervention en cas d’accident ou au niveau de dose 194 acceptable pour le radon domestique (niveaux tous supérieurs à la limite), • Les effets des expositions internes, qui sont difficiles à évaluer, tout (iii) les raisons pour lesquelles les limites ne sont pas applicables dans au moins sur une base dosimétrique identique à celle utilisée pour les les situations d’urgences, (iv) l’utilisation abusive de la dose collective expositions externes. En effet, la distribution spatiale de la dose peut et certaines de ses conclusions, (v) l’accent mis sur la protection de la être très hétérogène pour certains rayonnements, comme les émetteurs collectivité qui peut paraître s’effectuer au détriment de l’individu, etc. α, les émetteurs ß mous, les photons de faible énergie et les électrons Auger, particulièrement quand les radionucléides sont déposés dans En résumé, ces raisons pourraient sans doute justifier à elles seules des régions spécifiques de la cellule ou de l’organe. Dans ce cas, la une mise à plat des recommandations de 1990, afin de simplifier leur dose moyennée à l’organe ne peut être représentative du dommage utilisation et d’en supprimer certaines incohérences, qu’elles soient réelles potentiel et sous-estime le risque réel. ou apparentes. C’est dans cet esprit de simplification que le Président de la CIPR, Roger Clarke, a présenté au milieu des années 90 de nouveaux En résumé, les connaissances scientifiques acquises depuis une quinzaine concepts sur lesquels il proposait de centrer un nouveau système, comme d’années ne justifient ni un remaniement en profondeur du système de la dose maîtrisable (« controllable ») et la dose négligeable (« trivial »), protection ni des modifications notables des limites réglementaires ; le qui permettraient d’échapper à une catégorisation, poussée à l’extrême, risque de cancer radio-induit n’est que très faiblement revu à la baisse et des expositions. la quantification des maladies non cancéreuses et des effets des expositions internes demeure encore incertaine. Mais pour arriver à cette conclusion,

radio vol30 n4V2.indd 194 3/04/06 16:42:24 • Le risque de maladies non cancéreuses induites par les rayonnements, il était important de faire le point sur 15 années de résultats de travaux affectant les systèmes cardiovasculaire, pulmonaire et digestif, qui scientifiques. Le débat sur les effets des faibles doses, qui n’a pas perdu est confirmé. L’étude des relations dose-effet montre des incertitudes de son acuité, conduisait certains à vouloir réviser l’estimation du risque et ne permet pas de se prononcer sur l’existence ou non d’un seuil correspondant (à la hausse ou à la baisse). qui, s’il existe, pourrait se situer aux environs de 500 mSv. La CIPR reconnaît l’importance de ce type d’effets, mais, en l’état actuel des LES RAISONS TECHNIQUES ET PRATIQUES proviennent connaissances, est incapable de les inclure dans son estimation du essentiellement du retour d’expérience. L’application des recommandations risque global des faibles doses. de 1990 s’est avérée complexe et un grand nombre de problèmes pratiques a été difficile à résoudre. En fait, les difficultés rencontrées constituent, • Les effets des fortes doses, qui font l’objet d’un réexamen. La question pour la plupart, l’envers de la médaille de recommandations qui visaient de la valeur à attribuer à l’EBR (Efficacité Biologique Relative) de plus la perfection intellectuelle que le pragmatisme. Des exemples de chaque rayonnement en fonction de la dose n’est pas entièrement difficultés ou confusions sont fournis par : (i) la frontière entre pratique et résolue, pas plus que ne l’est la diminution de la nocivité en fonction de intervention, qui n’est pas évidente dans certaines situations durables et/ la diminution du débit de dose (problème des expositions prolongées ou anciennes, (ii) la limite de dose pour le public, fixée à 1 mSv, difficile pouvant résulter en des doses élevées, situées au-dessus des seuils des à comprendre lorsqu’elle est comparée au bruit de fond naturel, aux effets déterministes causés par des expositions aiguës). différents niveaux d’intervention en cas d’accident ou au niveau de dose acceptable pour le radon domestique (niveaux tous supérieurs à la limite), 195 • Les effets des expositions internes, qui sont difficiles à évaluer, tout (iii) les raisons pour lesquelles les limites ne sont pas applicables dans au moins sur une base dosimétrique identique à celle utilisée pour les les situations d’urgences, (iv) l’utilisation abusive de la dose collective expositions externes. En effet, la distribution spatiale de la dose peut et certaines de ses conclusions, (v) l’accent mis sur la protection de la être très hétérogène pour certains rayonnements, comme les émetteurs collectivité qui peut paraître s’effectuer au détriment de l’individu, etc. α, les émetteurs ß mous, les photons de faible énergie et les électrons Auger, particulièrement quand les radionucléides sont déposés dans En résumé, ces raisons pourraient sans doute justifier à elles seules des régions spécifiques de la cellule ou de l’organe. Dans ce cas, la une mise à plat des recommandations de 1990, afin de simplifier leur dose moyennée à l’organe ne peut être représentative du dommage utilisation et d’en supprimer certaines incohérences, qu’elles soient réelles potentiel et sous-estime le risque réel. ou apparentes. C’est dans cet esprit de simplification que le Président de la CIPR, Roger Clarke, a présenté au milieu des années 90 de nouveaux En résumé, les connaissances scientifiques acquises depuis une quinzaine concepts sur lesquels il proposait de centrer un nouveau système, comme d’années ne justifient ni un remaniement en profondeur du système de la dose maîtrisable (« controllable ») et la dose négligeable (« trivial »), protection ni des modifications notables des limites réglementaires ; le qui permettraient d’échapper à une catégorisation, poussée à l’extrême, risque de cancer radio-induit n’est que très faiblement revu à la baisse et des expositions. la quantification des maladies non cancéreuses et des effets des expositions internes demeure encore incertaine. Mais pour arriver à cette conclusion,

radio vol30 n4V2.indd 195 3/04/06 16:42:25 LES RAISONS SOCIETALES correspondent au besoin d’adapter les • En réponse à la question : protection de l’espèce humaine ou règles édictées par la CIPR à l’évolution des courants de pensée de la protection de l’ensemble du biotope, la CIPR fait le choix de considérer société moderne. De plus en plus, cette dernière a tendance à centrer ses l’ensemble, en situant l’être humain au sein de son environnement. intérêts sur le seul individu, occultant ainsi l’intérêt général. En outre, Certes la protection des espèces animales et végétales ne peut pas être la société actuelle accorde une attention grandissante à la qualité de son calquée directement sur celle de l’espèce humaine, ne serait-ce qu’en environnement, donc à la protection de la nature. En conséquence, il était raison des importances relatives qu’il convient d’attribuer aux intérêts normal que la CIPR reconsidère deux bases de sa doctrine en choisissant individuels et collectifs dans les deux domaines. Malgré les lacunes qui entre : (i) la persistance d’une éthique utilitariste ou un alignement sur une existent dans les connaissances, il semble justifié de mettre en place un éthique individualiste et (ii) la protection isolée de l’espèce humaine ou système consensuel de protection de la nature et de sa bio-diversité, la protection de l’ensemble du biotope, en replaçant l’être humain dans le en s’attachant à la sauvegarde du patrimoine naturel. Ce système cadre général de son environnement. doit demeurer compatible avec celui de la protection de l’homme en même temps qu’il s’insère dans le contexte général de la toxicologie • En réponse à la question : protection de la collectivité ou protection environnementale. Dans ce domaine comme dans le précédent, les de l’individu, la CIPR a estimé qu’elle se devait de renverser la considérations éthiques occupent une place prépondérante dans le dynamique de son système ; alors que l’approche adoptée en 1990 choix des options de base. La CIPR souhaite initier une tentative de pouvait se résumer par : si le risque pour la collectivité est maintenu standardisation de la protection, en mettant en perspective la protection 196 à un niveau acceptable, le risque individuel est aussi à un niveau contre les rayonnements, qu’il s’agisse de l’homme ou de la nature, et la acceptable, compte tenu de certaines barrières individuelles (limites et protection contre tous les autres agents nocifs, physiques ou chimiques. contraintes), l’approche actualisée devient : si le risque pour la santé L’ordre de priorité fixé jusqu’à présent - les travailleurs, la population de l’individu le plus exposé est négligeable, le risque total peut être et enfin l’environnement - risque d’être modifié, voire inversé. considéré comme négligeable, quel que soit le nombre de personnes exposées. Il faut cependant souligner, comme on le verra plus loin, • L’importance du dialogue social dans la prise de décisions, que l’appréciation de la dimension collective du risque n’est pas particulièrement dans le domaine de la protection de l’être humain abandonnée mais sa prise en compte relève davantage du jugement et de l’environnement constitue un troisième volet que la CIPR se d’expert que du résultat d’une approche mathématique automatique. devait de considérer. La mentalité passéiste qui peut se résumer par Il s’agit en fait d’un changement d’ordre éthique, qui fait basculer le « faites-nous confiance puisque nous sommes spécialistes » n’est système d’un ordre utilitariste à un ordre contractuel (ou pragmatique). plus acceptée. La CIPR, jusqu’aux années 80, édictait ses règles en En fait, la CIPR avait depuis quelques années recentré son intérêt sur cercle fermé et décidait « en sons âme et conscience » de la frontière l’individu, en raison notamment de l’émergence de problèmes liés aux entre l’acceptable et l’inacceptable. Lors de l’élaboration de ses personnes et non à la collectivité, comme la sensibilité individuelle recommandations de 1990, elle a révisé timidement son attitude en d’origine génétique, les indemnisations (maladies professionnelles et consultant les grandes organisations internationales et nationales, les séquelles d’accidents) ou plus généralement les conflits entre intérêt sociétés savantes et les partenaires sociaux. Ce processus a conduit général et intérêt particulier. à des modifications notables de ses propositions. Le dialogue social

radio vol30 n4V2.indd 196 3/04/06 16:42:25 LES RAISONS SOCIETALES correspondent au besoin d’adapter les • En réponse à la question : protection de l’espèce humaine ou règles édictées par la CIPR à l’évolution des courants de pensée de la protection de l’ensemble du biotope, la CIPR fait le choix de considérer société moderne. De plus en plus, cette dernière a tendance à centrer ses l’ensemble, en situant l’être humain au sein de son environnement. intérêts sur le seul individu, occultant ainsi l’intérêt général. En outre, Certes la protection des espèces animales et végétales ne peut pas être la société actuelle accorde une attention grandissante à la qualité de son calquée directement sur celle de l’espèce humaine, ne serait-ce qu’en environnement, donc à la protection de la nature. En conséquence, il était raison des importances relatives qu’il convient d’attribuer aux intérêts normal que la CIPR reconsidère deux bases de sa doctrine en choisissant individuels et collectifs dans les deux domaines. Malgré les lacunes qui entre : (i) la persistance d’une éthique utilitariste ou un alignement sur une existent dans les connaissances, il semble justifié de mettre en place un éthique individualiste et (ii) la protection isolée de l’espèce humaine ou système consensuel de protection de la nature et de sa bio-diversité, la protection de l’ensemble du biotope, en replaçant l’être humain dans le en s’attachant à la sauvegarde du patrimoine naturel. Ce système cadre général de son environnement. doit demeurer compatible avec celui de la protection de l’homme en même temps qu’il s’insère dans le contexte général de la toxicologie • En réponse à la question : protection de la collectivité ou protection environnementale. Dans ce domaine comme dans le précédent, les de l’individu, la CIPR a estimé qu’elle se devait de renverser la considérations éthiques occupent une place prépondérante dans le dynamique de son système ; alors que l’approche adoptée en 1990 choix des options de base. La CIPR souhaite initier une tentative de pouvait se résumer par : si le risque pour la collectivité est maintenu standardisation de la protection, en mettant en perspective la protection à un niveau acceptable, le risque individuel est aussi à un niveau contre les rayonnements, qu’il s’agisse de l’homme ou de la nature, et la 197 acceptable, compte tenu de certaines barrières individuelles (limites et protection contre tous les autres agents nocifs, physiques ou chimiques. contraintes), l’approche actualisée devient : si le risque pour la santé L’ordre de priorité fixé jusqu’à présent - les travailleurs, la population de l’individu le plus exposé est négligeable, le risque total peut être et enfin l’environnement - risque d’être modifié, voire inversé. considéré comme négligeable, quel que soit le nombre de personnes exposées. Il faut cependant souligner, comme on le verra plus loin, • L’importance du dialogue social dans la prise de décisions, que l’appréciation de la dimension collective du risque n’est pas particulièrement dans le domaine de la protection de l’être humain abandonnée mais sa prise en compte relève davantage du jugement et de l’environnement constitue un troisième volet que la CIPR se d’expert que du résultat d’une approche mathématique automatique. devait de considérer. La mentalité passéiste qui peut se résumer par Il s’agit en fait d’un changement d’ordre éthique, qui fait basculer le « faites-nous confiance puisque nous sommes spécialistes » n’est système d’un ordre utilitariste à un ordre contractuel (ou pragmatique). plus acceptée. La CIPR, jusqu’aux années 80, édictait ses règles en En fait, la CIPR avait depuis quelques années recentré son intérêt sur cercle fermé et décidait « en sons âme et conscience » de la frontière l’individu, en raison notamment de l’émergence de problèmes liés aux entre l’acceptable et l’inacceptable. Lors de l’élaboration de ses personnes et non à la collectivité, comme la sensibilité individuelle recommandations de 1990, elle a révisé timidement son attitude en d’origine génétique, les indemnisations (maladies professionnelles et consultant les grandes organisations internationales et nationales, les séquelles d’accidents) ou plus généralement les conflits entre intérêt sociétés savantes et les partenaires sociaux. Ce processus a conduit général et intérêt particulier. à des modifications notables de ses propositions. Le dialogue social

radio vol30 n4V2.indd 197 3/04/06 16:42:26 généralisé et étendu apparaît aujourd’hui essentiel, qu’il s’agisse de LE PROJET DES NOUVELLES RECOMMANDATIONS la protection contre les rayonnements ou tout autre agent nocif pour la santé. Il constitue sûrement un pilier de l’acceptabilité d’un certain Depuis 2001, la CIPR travaille sur un projet de nouvelles recommandations, niveau de risque individuel et collectif. En optant pour la transparence qui se dénomment Recommandations 2005, car destinées en principe à être la CIPR a changé ses habitudes, via des consultations répétées auprès finalisés en 2005, qui correspond à la fin du mandat des membres actuels6. des institutions intéressées, qu’elles soient scientifiques, techniques, La CIPR note que ces nouvelles recommandations constituent une évolution politiques ou représentatives de divers groupes de pression. En fait, la naturelle et un éclaircissement des précédentes recommandations. Elle CIPR n’a rien inventé et n’est même pas avant-gardiste sur ce terrain, rappelle qu’elles doivent assurer un niveau de protection qui doit être puisqu’elle n’a fait que s’aligner sur les autres organisations, en tenant considéré comme une obligation et que le non-respect des niveaux de compte des nouveaux modes de gestion des activités à risque. protections indiqués constitue un échec. Les principales modifications qui constituent un démarquage notable par rapport aux recommandations 1990 En résumé, les trois raisons sociétales décrites ci-dessus ont des poids peuvent se résumer de la façon suivante 7 : différents dans la justification d’un changement des règles du jeu de la radioprotection : (1) Le privilège que la CIPR déclare accorder à l’individu LES PRINCIPES DE BASE de protection : Justification des pratiques, plutôt qu’à la société était déjà sous-jacent dans les recommandations de Optimisation de la protection et Limitation des expositions, sont conservés 1990, qui ont créé implicitement une échelle de risque avec notamment le mais remaniés dans leur hiérarchie, leur signification et leur application. 198 concept de contrainte, qui s’applique à une source de rayonnements donnée La CIPR rappelle que la justification, qui par définition ne peut s’appliquer mais concerne l’individu et constitue la borne supérieure pour la sélection qu’aux situations d’exposition introduites ou poursuivies délibérément, des options de protection individuelle ; (2) la décision de considérer la c’est-à-dire aux pratiques donnant lieu à des expositions normales, repose protection de l’espèce humaine dans le cadre de la protection de l’ensemble sur des considérations très diverses parmi lesquelles celles relatives à la du biotope constitue une avancée louable, et le fait que la CIPR ait radioprotection n’occupent qu’une part souvent réduite ; les jugements devancé d’autres initiatives prévisibles est un gage de cohérence entre les incombent finalement à des décideurs, souvent au niveau gouvernemental. systèmes de protection des espèces vivantes ; (3) l’implication des parties C’est pourquoi la CIPR, tout en conservant ce principe qui constitue un prenantes, particulièrement dans les aspects décisionnels, relève plus du préalable obligatoire à son système de protection, le juge largement en domaine social ou politique, au même titre que le principe de justification, dehors de sa compétence et de sa responsabilité. La CIPR met l’accent sur qui constituait le premier pilier du système de 1990 et qui est maintenant le troisième principe, qui devient la Restriction de la dose individuelle en jugé largement en dehors du champ des recommandations ; il semble donc rapport avec une source de rayonnements (la source dominante), qui qu’il y ait ici une contradiction et que la CIPR dans ce cas se préoccupe des s’applique désormais avant l’optimisation. Cette modification exprime le règles de fonctionnement des sociétés, dont certaines relèvent des autorités souci de la CIPR de focaliser son système de protection sur l’individu et nationales. En conclusion, la protection de l’environnement vivant est le d’en faciliter l’application. seul point nouveau que la CIPR se devait d’aborder ; en revanche, à elle seule, elle ne peut justifier un changement radical des règles de protection de l’espèce humaine ; l’inverse n’est d’ailleurs pas plus concevable.

radio vol30 n4V2.indd 198 3/04/06 16:42:27 généralisé et étendu apparaît aujourd’hui essentiel, qu’il s’agisse de LE PROJET DES NOUVELLES RECOMMANDATIONS la protection contre les rayonnements ou tout autre agent nocif pour la santé. Il constitue sûrement un pilier de l’acceptabilité d’un certain Depuis 2001, la CIPR travaille sur un projet de nouvelles recommandations, niveau de risque individuel et collectif. En optant pour la transparence qui se dénomment Recommandations 2005, car destinées en principe à être la CIPR a changé ses habitudes, via des consultations répétées auprès finalisés en 2005, qui correspond à la fin du mandat des membres actuels6. des institutions intéressées, qu’elles soient scientifiques, techniques, La CIPR note que ces nouvelles recommandations constituent une évolution politiques ou représentatives de divers groupes de pression. En fait, la naturelle et un éclaircissement des précédentes recommandations. Elle CIPR n’a rien inventé et n’est même pas avant-gardiste sur ce terrain, rappelle qu’elles doivent assurer un niveau de protection qui doit être puisqu’elle n’a fait que s’aligner sur les autres organisations, en tenant considéré comme une obligation et que le non-respect des niveaux de compte des nouveaux modes de gestion des activités à risque. protections indiqués constitue un échec. Les principales modifications qui constituent un démarquage notable par rapport aux recommandations 1990 En résumé, les trois raisons sociétales décrites ci-dessus ont des poids peuvent se résumer de la façon suivante 7 : différents dans la justification d’un changement des règles du jeu de la radioprotection : (1) Le privilège que la CIPR déclare accorder à l’individu LES PRINCIPES DE BASE de protection : Justification des pratiques, plutôt qu’à la société était déjà sous-jacent dans les recommandations de Optimisation de la protection et Limitation des expositions, sont conservés 1990, qui ont créé implicitement une échelle de risque avec notamment le mais remaniés dans leur hiérarchie, leur signification et leur application. concept de contrainte, qui s’applique à une source de rayonnements donnée La CIPR rappelle que la justification, qui par définition ne peut s’appliquer 199 mais concerne l’individu et constitue la borne supérieure pour la sélection qu’aux situations d’exposition introduites ou poursuivies délibérément, des options de protection individuelle ; (2) la décision de considérer la c’est-à-dire aux pratiques donnant lieu à des expositions normales, repose protection de l’espèce humaine dans le cadre de la protection de l’ensemble sur des considérations très diverses parmi lesquelles celles relatives à la du biotope constitue une avancée louable, et le fait que la CIPR ait radioprotection n’occupent qu’une part souvent réduite ; les jugements devancé d’autres initiatives prévisibles est un gage de cohérence entre les incombent finalement à des décideurs, souvent au niveau gouvernemental. systèmes de protection des espèces vivantes ; (3) l’implication des parties C’est pourquoi la CIPR, tout en conservant ce principe qui constitue un prenantes, particulièrement dans les aspects décisionnels, relève plus du préalable obligatoire à son système de protection, le juge largement en domaine social ou politique, au même titre que le principe de justification, dehors de sa compétence et de sa responsabilité. La CIPR met l’accent sur qui constituait le premier pilier du système de 1990 et qui est maintenant le troisième principe, qui devient la Restriction de la dose individuelle en jugé largement en dehors du champ des recommandations ; il semble donc rapport avec une source de rayonnements (la source dominante), qui qu’il y ait ici une contradiction et que la CIPR dans ce cas se préoccupe des s’applique désormais avant l’optimisation. Cette modification exprime le règles de fonctionnement des sociétés, dont certaines relèvent des autorités souci de la CIPR de focaliser son système de protection sur l’individu et nationales. En conclusion, la protection de l’environnement vivant est le d’en faciliter l’application. seul point nouveau que la CIPR se devait d’aborder ; en revanche, à elle seule, elle ne peut justifier un changement radical des règles de protection de l’espèce humaine ; l’inverse n’est d’ailleurs pas plus concevable. 6 La dernière version du projet, discutée par la CIPR en octobre 2004, peut être consultée sur le site internet de la CIPR. 7 D’après le résumé et le texte du projet des Recommandations 2005, présentés sur internet.

radio vol30 n4V2.indd 199 3/04/06 16:42:27 Le niveau fondamental de protection est la restriction appliquée à la de rayonnements. Cette exigence d’optimisation, implique, comme par le dose individuelle résultant d’une source donnée ; c’est la contrainte de passé, que toutes les expositions soient aussi basses que raisonnablement dose. Celle-ci doit assurer un niveau de protection aux personnes les plus possible, compte tenu des facteurs économiques et sociaux. Cette exigence exposées dans une catégorie d’exposition (professionnelle, publique, ne peut pas s’exprimer en termes quantitatifs de portée générale ; les médicale), dans toutes les situations relevant du champ d’application des opérateurs et les autorités nationales responsables de la protection doivent recommandations. Exception faite de l’exposition des patients irradiés porter des jugements spécifiques à chaque situation cause de l’exposition pour raisons médicales, la contrainte constitue le niveau de base de d’individus. En fait, l’optimisation de la protection va plus loin que la protection, qui doit être atteint dans les situations normales, les accidents simple réduction des doses reçues par les travailleurs et le public dans et les urgences, ainsi que dans le cas d’exposition maîtrisable préexistante. des situations normales, car elle doit s’intéresser aussi à la prévention des La contrainte de dose ne représente pas une démarcation entre la zone des accidents et à toutes les autres sources d’expositions potentielles. « doses dangereuses » et celle des « doses sans danger ». Un dépassement de la contrainte de dose ne signifie en aucun cas le franchissement d’un cap dans l’échelle des risques ; ce dépassement est toujours synonyme d’échec et peut même constituer une infraction répréhensible, si les autorités nationales lui ont conféré ce statut.

200 La CIPR indique quatre valeurs maximales de contraintes (exprimées en dose efficace), pour les travailleurs et les personnes du public, regroupant plusieurs situations d’exposition à une source, prédominante sur toutes les autres sources. Le Tableau 1 résume les caractéristiques des situations répondant à ces critères et fournit des exemples concrets. Ces valeurs maximales ont pour but d’aider les autorités nationales dans le choix des contraintes réglementaires ou non ; ces dernières sont évidemment inférieures aux valeurs maximales indiquées plus haut ; la CIPR estime que, raisonnablement, la réduction ne devrait pas dépasser un facteur 10.

Les contraintes de dose doivent être complétées par une optimisation du niveau de protection. Cette démarche est rendue nécessaire du fait de l’existence d’une certaine probabilité d’effets néfastes sur la santé, quel que soit le niveau de l’exposition reçue en plus de l’exposition d’origine naturelle. C’est la raison pour laquelle la CIPR recommande que des mesures supplémentaires, plus strictes que celles qui conduisent à la détermination des contraintes de dose, soient envisagées pour chaque source

radio vol30 n4V2.indd 200 3/04/06 16:42:28 Le niveau fondamental de protection est la restriction appliquée à la de rayonnements. Cette exigence d’optimisation, implique, comme par le dose individuelle résultant d’une source donnée ; c’est la contrainte de passé, que toutes les expositions soient aussi basses que raisonnablement dose. Celle-ci doit assurer un niveau de protection aux personnes les plus possible, compte tenu des facteurs économiques et sociaux. Cette exigence exposées dans une catégorie d’exposition (professionnelle, publique, ne peut pas s’exprimer en termes quantitatifs de portée générale ; les médicale), dans toutes les situations relevant du champ d’application des opérateurs et les autorités nationales responsables de la protection doivent recommandations. Exception faite de l’exposition des patients irradiés porter des jugements spécifiques à chaque situation cause de l’exposition pour raisons médicales, la contrainte constitue le niveau de base de d’individus. En fait, l’optimisation de la protection va plus loin que la protection, qui doit être atteint dans les situations normales, les accidents simple réduction des doses reçues par les travailleurs et le public dans et les urgences, ainsi que dans le cas d’exposition maîtrisable préexistante. des situations normales, car elle doit s’intéresser aussi à la prévention des La contrainte de dose ne représente pas une démarcation entre la zone des accidents et à toutes les autres sources d’expositions potentielles. « doses dangereuses » et celle des « doses sans danger ». Un dépassement Situations d’exposition de la contrainte de dose ne signifie en aucun cas le franchissement d’un cap Contraintes dans l’échelle des risques ; ce dépassement est toujours synonyme d’échec (mSv en 1 an) Caractéristiques des situations Exemples concrets de situations et peut même constituer une infraction répréhensible, si les autorités • Aucun bénéfice • Urgences, uniquement pour sauver des individuel ousociétal vies humaines nationales lui ont conféré ce statut. 100 • Difficilement maîtrisable • Bénéfice individuel direct ou • Urgences La CIPR indique quatre valeurs maximales de contraintes (exprimées en indirect Quand les mesures de protection sont 201 dose efficace), pour les travailleurs et les personnes du public, regroupant • Information précise du public, difficiles à mettre en œuvre formation et surveillance des plusieurs situations d’exposition à une source, prédominante sur toutes travailleurs 20 les autres sources. Le Tableau 1 résume les caractéristiques des situations • Facilement maîtrisable • Exposition professionnelle en général répondant à ces critères et fournit des exemples concrets. Ces valeurs • Bénéfice individuel direct ou • Expositions préexistantes indirect • Exposition des personnes du public maximales ont pour but d’aider les autorités nationales dans le choix • Information et évaluation de dans les urgences, quand les mesures des contraintes réglementaires ou non ; ces dernières sont évidemment l’exposition du public, formation de protection sont faciles à mettre en et surveillance des travailleurs oeuvre inférieures aux valeurs maximales indiquées plus haut ; la CIPR estime • Exposition des accompagnateurs que, raisonnablement, la réduction ne devrait pas dépasser un facteur 10. et soignants de patients (domaine médical) 1 • Facilement maîtrisable • Exposition des personnes du public Les contraintes de dose doivent être complétées par une optimisation du • Bénéfice sociétal, mais en général niveau de protection. Cette démarche est rendue nécessaire du fait de pas de bénéfice individuel direct • Information générale, pas de l’existence d’une certaine probabilité d’effets néfastes sur la santé, quel formation, pas d’évaluation que soit le niveau de l’exposition reçue en plus de l’exposition d’origine individuelle de l’exposition 0,01 naturelle. C’est la raison pour laquelle la CIPR recommande que des • Utilité du contrôle sujette mesures supplémentaires, plus strictes que celles qui conduisent à la à appréciation • Toutes les situations d’expositions détermination des contraintes de dose, soient envisagées pour chaque source TABLEAU 1. Contraintes de dose maximales, selon les situations d’exposition, pour une source dominante

radio vol30 n4V2.indd 201 3/04/06 16:42:29 Le niveau de protection défini pour un individu vis-à-vis de toutes L’ENGAGEMENT DES PARTIES PRENANTES constitue aussi une les sources, dans une catégorie d’exposition donnée et dans les seules nouveauté pour des recommandations de la CIPR. Selon cette dernière, situations normales, est la limite de dose. Il est rare qu’il soit possible la démarche d’optimisation doit s’effectuer avec le concours de toutes d’évaluer l’exposition totale d’une personne due à toutes les sources les parties impliquées dans une conjoncture donnée qui les inquiète en maîtrisables. La comparaison de cette exposition totale et de la limite, raison du danger d’éventuelles conséquences. L’expérience prouve que effectuée afin de vérifier le respect de la réglementation, ne peut donc cet engagement permet (i) l’intégration de nombreux paramètres dans les être qu’approximative ; cette approximation est moindre pour l’exposition prises de décision, (ii) l’amélioration de la qualité finale des décisions, des travailleurs que pour celle des personnes du public. La CIPR estime (iii) la résolution de conflits d’intérêts contradictoires, (iv) l’établissement que les limites de dose (dose efficace) recommandées en 1991 dans sa d’un état de confiance envers les institutions, ainsi que (v) l’éducation des Publication 60 procurent un niveau suffisant de protection dans les professionnels et du public. En outre, l’engagement des parties prenantes situations normales. En conséquence, elle maintient pour les travailleurs renforce la culture de sûreté et permet d’introduire une certaine souplesse la limite de 20 mSv par an (moyennée sur 5 ans, soit 100 mSv en 5 ans) et dans la gestion du risque radiologique, garante de décisions efficaces et pour le public celle de 1 mSv (pouvant atteindre certaines années 5 mSv durables. dans la mesure où la moyenne sur 5 ans ne dépasse pas 1 mSv par an). Il convient de rappeler qu’à l’inverse de la contrainte la limite de dose L’EXCLUSION de sources de rayonnements en dehors de la portée n’a aucun sens en dehors des situations normales, par exemple dans les des recommandations de la CIPR s’applique aux sources qui délivrent 202 situations accidentelles. des doses efficaces annuelles très basses et qui sont souvent difficiles ou impossibles à maîtriser. L’actuel projet recommande les niveaux En résumé, les principes généraux qui assurent aux personnes le niveau d’exclusion suivants, exprimés en concentration d’activité : pour les requis de protection reposent en premier lieu sur les contraintes (relatives émetteurs α artificiels : 0,01 Bq par gramme ; pour les émetteurs ß et à une source donnée de rayonnements) assujetties à l’optimisation, qui γ artificiels: 0,1 Bq par gramme ; pour les radionucléides naturels situés s’appliquent quelle que soit la situation, et secondairement sur les limites au début des chaînes de désintégration, par exemple l’Uranium 238 et le (relatives à l’ensemble des sources d’exposition individuelle) qui ne Thorium 232 : 1,0 Bq par gramme, ou encore le potassium 40 : 10 Bq s’appliquent qu’aux situations normales. par gramme. Ces valeurs d’exclusion constitueraient les bornes au-dessus desquelles les radionucléides seraient considérés comme des produits LA CULTURE DE SURETE apparaît pour la première fois dans des radioactifs. recommandations générales de la CIPR ; elle est considérée comme un corollaire du processus d’optimisation, qui doit l’encourager et la susciter. Les L’exclusion constitue sans doute le chapitre des nouvelles recommandations responsables de la radioprotection doivent régulièrement se poser la question : le plus contesté. Un des points principaux de la contestation met en cause ai-je fait tout ce qui est raisonnablement en mon pouvoir pour éviter ou réduire le jugement par lequel le risque d’une dose est considéré négligeable. En les doses ? Cette interrogation, qui s’adresse au jugement, nécessite, pour être fait, la décision fait appel à un jugement de valeur, dès lors que la relation résolue de façon satisfaisante, la coopération de toutes les parties impliquées, dose-effet est supposée linéaire et sans seuil. La discussion est semblable au minimum constituées par les responsables opérationnels et les autorités. à celle du passé au sujet du concept « de minimis », qui reposait sur

radio vol30 n4V2.indd 202 3/04/06 16:42:30 Le niveau de protection défini pour un individu vis-à-vis de toutes L’ENGAGEMENT DES PARTIES PRENANTES constitue aussi une les sources, dans une catégorie d’exposition donnée et dans les seules nouveauté pour des recommandations de la CIPR. Selon cette dernière, situations normales, est la limite de dose. Il est rare qu’il soit possible la démarche d’optimisation doit s’effectuer avec le concours de toutes d’évaluer l’exposition totale d’une personne due à toutes les sources les parties impliquées dans une conjoncture donnée qui les inquiète en maîtrisables. La comparaison de cette exposition totale et de la limite, raison du danger d’éventuelles conséquences. L’expérience prouve que effectuée afin de vérifier le respect de la réglementation, ne peut donc cet engagement permet (i) l’intégration de nombreux paramètres dans les être qu’approximative ; cette approximation est moindre pour l’exposition prises de décision, (ii) l’amélioration de la qualité finale des décisions, des travailleurs que pour celle des personnes du public. La CIPR estime (iii) la résolution de conflits d’intérêts contradictoires, (iv) l’établissement que les limites de dose (dose efficace) recommandées en 1991 dans sa d’un état de confiance envers les institutions, ainsi que (v) l’éducation des Publication 60 procurent un niveau suffisant de protection dans les professionnels et du public. En outre, l’engagement des parties prenantes situations normales. En conséquence, elle maintient pour les travailleurs renforce la culture de sûreté et permet d’introduire une certaine souplesse la limite de 20 mSv par an (moyennée sur 5 ans, soit 100 mSv en 5 ans) et dans la gestion du risque radiologique, garante de décisions efficaces et pour le public celle de 1 mSv (pouvant atteindre certaines années 5 mSv durables. dans la mesure où la moyenne sur 5 ans ne dépasse pas 1 mSv par an). Il convient de rappeler qu’à l’inverse de la contrainte la limite de dose L’EXCLUSION de sources de rayonnements en dehors de la portée n’a aucun sens en dehors des situations normales, par exemple dans les des recommandations de la CIPR s’applique aux sources qui délivrent situations accidentelles. des doses efficaces annuelles très basses et qui sont souvent difficiles 203 ou impossibles à maîtriser. L’actuel projet recommande les niveaux En résumé, les principes généraux qui assurent aux personnes le niveau d’exclusion suivants, exprimés en concentration d’activité : pour les requis de protection reposent en premier lieu sur les contraintes (relatives émetteurs α artificiels : 0,01 Bq par gramme ; pour les émetteurs ß et à une source donnée de rayonnements) assujetties à l’optimisation, qui γ artificiels: 0,1 Bq par gramme ; pour les radionucléides naturels situés s’appliquent quelle que soit la situation, et secondairement sur les limites au début des chaînes de désintégration, par exemple l’Uranium 238 et le (relatives à l’ensemble des sources d’exposition individuelle) qui ne Thorium 232 : 1,0 Bq par gramme, ou encore le potassium 40 : 10 Bq s’appliquent qu’aux situations normales. par gramme. Ces valeurs d’exclusion constitueraient les bornes au-dessus desquelles les radionucléides seraient considérés comme des produits LA CULTURE DE SURETE apparaît pour la première fois dans des radioactifs. recommandations générales de la CIPR ; elle est considérée comme un corollaire du processus d’optimisation, qui doit l’encourager et la susciter. Les L’exclusion constitue sans doute le chapitre des nouvelles recommandations responsables de la radioprotection doivent régulièrement se poser la question : le plus contesté. Un des points principaux de la contestation met en cause ai-je fait tout ce qui est raisonnablement en mon pouvoir pour éviter ou réduire le jugement par lequel le risque d’une dose est considéré négligeable. En les doses ? Cette interrogation, qui s’adresse au jugement, nécessite, pour être fait, la décision fait appel à un jugement de valeur, dès lors que la relation résolue de façon satisfaisante, la coopération de toutes les parties impliquées, dose-effet est supposée linéaire et sans seuil. La discussion est semblable au minimum constituées par les responsables opérationnels et les autorités. à celle du passé au sujet du concept « de minimis », qui reposait sur

radio vol30 n4V2.indd 203 3/04/06 16:42:30 l’argument suivant : le risque peut être ignoré puisqu’il est petit. En fait, LA PROTECTION DES ESPECES NON HUMAINES est le dernier un risque négligeable n’est pas nécessairement acceptable (acceptable volet réellement novateur des recommandations 2005. Il était annoncé par pour qui ?) et un risque acceptable n’est pas nécessairement négligeable8. la Publication 91 sur la protection de l’environnement9, dont les grandes De plus, l’addition de risques négligeables peut aboutir à un risque lignes sont reprises dans le projet des futures recommandations. La CIPR conséquent, et l’exposition d’un grand nombre de personnes peut signifier indique que le nouveau système est conçu pour constituer un ensemble que de nombreuses personnes en subiront des conséquences néfastes. On harmonieux et cohérent de la protection de l’ensemble des espèces retrouve ici l’opposition entre intérêt individuel et intérêt général. On peut vivantes, humaine, animales et végétales. Elle ajoute qu’elle a l’intention donc s’attendre à ce que les propositions qui figurent dans l’actuel projet de constituer des jeux de répertoires et modèles dosimétriques de référence, soient amendées dans le prochain projet. ainsi que des données permettant d’apprécier les relations exposition- dose et dose-effet ; l’interprétation des résultats sera développée pour LES GRANDEURS DOSIMETRIQUES sont simplifiées, en raison des un nombre limité d’animaux et de plantes types. Cet ensemble permettra nombreuses confusions qui ont eu lieu entre les trois grandeurs utilisées de garantir que la protection des humains et celle des autres organismes précédemment : dose équivalente, équivalent de dose et dose efficace, toutes vivants reposent sur les mêmes bases scientifiques, particulièrement en exprimées par la même unité le sievert. La CIPR propose de supprimer le ce qui concerne les relations exposition-dose et dose-effet au niveau de terme « dose équivalente » (combinaison de la dose absorbée et du facteur la molécule, de la cellule, du tissu, de l’organe et de l’organisme dans son

de pondération pour les rayonnements wR) et de le remplacer par celui de ensemble. La CIPR espère être en mesure de proposer pour les animaux et 204 dose pondérée pour les rayonnements, en attendant de lui trouver une les plantes, par analogie au système pour l’être humain qui repose sur la meilleure appellation. La définition de la dose efficace demeure inchangée : contrainte de dose, un ensemble de « niveaux de considération dérivés »

c’est la dose absorbée multipliée par les deux facteurs de pondération wR pour l’environnement ambiant, qui pourrait constituer une base pour des

pour les rayonnements et wT pour les tissus. La CIPR fournit de nouvelles normes internationales, dont le besoin devient de plus en plus fort. valeurs pour ces deux facteurs de pondération, en raison d’avancées dans les

connaissances. Le facteur de pondération pour les rayonnements wR prend les valeurs suivantes : 1 pour les photons de toutes énergies, 1 pour les électrons LES CONSÉQUENCES PRATIQUES DU CHANGEMENT et muons de toutes énergies, 2 pour les protons autres que les protons de recul (d’énergie supérieure ou égale à 2 MeV), 20 pour les émetteurs α, les Les conséquences de ces modifications sont essentiellement d’ordre fragments de fission et les noyaux lourds ; une courbe lissée est recommandée conceptuel. Les nouvelles recommandations se distinguent de celles de pour les neutrons en fonction de leur énergie. Le facteur de pondération pour 1990 par deux caractéristiques principales : simplification du système et

les tissus wT est plus profondément remanié que le précédent, sur la base de adaptation au courant de pensée moderne. nouvelles données épidémiologiques, qui ont permis d’allonger la liste tout

en la simplifiant. Les nouvelles valeurs de wT sont regroupées dans quatre LA SIMPLIFICATION réside dans la création d’un système nettement catégories : 0,12 pour la moelle osseuse, le sein, le colon, les poumons et plus général et moins compartimenté que le précédent, qui distinguait les l’estomac ; 0,05 pour la vessie, l’œsophage, les gonades, le foie et la thyroïde ; pratiques et les interventions, les expositions réellement existantes et les 0,01 pour la surface osseuse, le cerveau, les reins, les glandes salivaires et la expositions potentielles, les catégories d’expositions, etc. Ces distinctions peau ; 0,10 pour les autres tissus (14 au total). étaient en grande partie dues au choix du concept de limite comme base du

radio vol30 n4V2.indd 204 3/04/06 16:42:31 l’argument suivant : le risque peut être ignoré puisqu’il est petit. En fait, LA PROTECTION DES ESPECES NON HUMAINES est le dernier un risque négligeable n’est pas nécessairement acceptable (acceptable volet réellement novateur des recommandations 2005. Il était annoncé par pour qui ?) et un risque acceptable n’est pas nécessairement négligeable8. la Publication 91 sur la protection de l’environnement9, dont les grandes De plus, l’addition de risques négligeables peut aboutir à un risque lignes sont reprises dans le projet des futures recommandations. La CIPR conséquent, et l’exposition d’un grand nombre de personnes peut signifier indique que le nouveau système est conçu pour constituer un ensemble que de nombreuses personnes en subiront des conséquences néfastes. On harmonieux et cohérent de la protection de l’ensemble des espèces retrouve ici l’opposition entre intérêt individuel et intérêt général. On peut vivantes, humaine, animales et végétales. Elle ajoute qu’elle a l’intention donc s’attendre à ce que les propositions qui figurent dans l’actuel projet de constituer des jeux de répertoires et modèles dosimétriques de référence, soient amendées dans le prochain projet. ainsi que des données permettant d’apprécier les relations exposition- dose et dose-effet ; l’interprétation des résultats sera développée pour LES GRANDEURS DOSIMETRIQUES sont simplifiées, en raison des un nombre limité d’animaux et de plantes types. Cet ensemble permettra nombreuses confusions qui ont eu lieu entre les trois grandeurs utilisées de garantir que la protection des humains et celle des autres organismes précédemment : dose équivalente, équivalent de dose et dose efficace, toutes vivants reposent sur les mêmes bases scientifiques, particulièrement en exprimées par la même unité le sievert. La CIPR propose de supprimer le ce qui concerne les relations exposition-dose et dose-effet au niveau de terme « dose équivalente » (combinaison de la dose absorbée et du facteur la molécule, de la cellule, du tissu, de l’organe et de l’organisme dans son de pondération pour les rayonnements wR) et de le remplacer par celui de ensemble. La CIPR espère être en mesure de proposer pour les animaux et dose pondérée pour les rayonnements, en attendant de lui trouver une les plantes, par analogie au système pour l’être humain qui repose sur la 205 meilleure appellation. La définition de la dose efficace demeure inchangée : contrainte de dose, un ensemble de « niveaux de considération dérivés » c’est la dose absorbée multipliée par les deux facteurs de pondération wR pour l’environnement ambiant, qui pourrait constituer une base pour des pour les rayonnements et wT pour les tissus. La CIPR fournit de nouvelles normes internationales, dont le besoin devient de plus en plus fort. valeurs pour ces deux facteurs de pondération, en raison d’avancées dans les connaissances. Le facteur de pondération pour les rayonnements wR prend les valeurs suivantes : 1 pour les photons de toutes énergies, 1 pour les électrons LES CONSÉQUENCES PRATIQUES DU CHANGEMENT et muons de toutes énergies, 2 pour les protons autres que les protons de recul (d’énergie supérieure ou égale à 2 MeV), 20 pour les émetteurs α, les Les conséquences de ces modifications sont essentiellement d’ordre fragments de fission et les noyaux lourds ; une courbe lissée est recommandée conceptuel. Les nouvelles recommandations se distinguent de celles de pour les neutrons en fonction de leur énergie. Le facteur de pondération pour 1990 par deux caractéristiques principales : simplification du système et les tissus wT est plus profondément remanié que le précédent, sur la base de adaptation au courant de pensée moderne. nouvelles données épidémiologiques, qui ont permis d’allonger la liste tout en la simplifiant. Les nouvelles valeurs de wT sont regroupées dans quatre LA SIMPLIFICATION réside dans la création d’un système nettement catégories : 0,12 pour la moelle osseuse, le sein, le colon, les poumons et plus général et moins compartimenté que le précédent, qui distinguait les l’estomac ; 0,05 pour la vessie, l’œsophage, les gonades, le foie et la thyroïde ; pratiques et les interventions, les expositions réellement existantes et les 0,01 pour la surface osseuse, le cerveau, les reins, les glandes salivaires et la expositions potentielles, les catégories d’expositions, etc. Ces distinctions peau ; 0,10 pour les autres tissus (14 au total). étaient en grande partie dues au choix du concept de limite comme base du 8 D’après Bo Lindell, Président de la CIPR de 1977 à 1985, dans : How safe is safe enough ? (Lauriston Taylor lectures in Radiation Protection and Measurements Lecture N° 12, Bethesda, MD, NCRP, 1988.

radio vol30 n4V2.indd 205 3/04/06 16:42:32 système de restriction des doses. Les recommandations 2005 choisissent le stochastiques. La dose équivalente de 1990 ne sert qu’à exprimer le risque concept de contrainte de dose comme niveau fondamental, indépendamment pour un organe ou un tissu particulier ; elle change de nom (provisoirement du type d’exposition et de la situation. Le contrôle s’effectue dorénavant dose pondérée pour les rayonnements), afin de montrer l’usage limité qui sur la dose due à la source d’exposition principale (dominante) et non sur la doit en être fait. dose totale due à l’ensemble des sources. En outre et surtout, la contrainte 2005 a une portée beaucoup plus large que la limite 1990. Elle permet de L’ADAPTATION AU COURANT DE PENSEE MODERNE donne gérer les différentes situations d’exposition à l’aide d’une échelle unique la prédominance à la protection de l’individu, en supposant que, si cette comportant seulement quatre valeurs de contraintes de dose. Ces quatre dernière est performante, la collectivité est protégée à des niveaux de niveaux ne remplacent pas l’ensemble des niveaux de référence, d’action, protection équivalents. Les efforts de protection se focalisent sur la source d’investigation, d’intervention, etc. (actuellement au nombre d’environ de rayonnements affectant l’individu de façon prédominante (source- 25), à l’origine de nombreuses confusions. La nouvelle présentation se related), et non plus sur l’individu affecté par l’ensemble des sources de borne à placer au second plan les anciens niveaux opérationnels mais elle son environnement (individual-related). Il en résulte que les restrictions les situe dans une rationalité globale associée aux situations d’exposition. s’appliquent dorénavant à la source et non à l’individu. Cette approche, Elle présente l’avantage de mettre en évidence le continuum des risques et située à l’opposé de la doctrine passée de la CIPR, devrait conduire leur appréciation en fonction des caractéristiques de l’exposition (maîtrise, elle aussi à une grande simplification des pratiques quotidiennes de la bénéfice individuel, information…). En plus de son intérêt simplificateur, radioprotection. 206 la contrainte, en tant qu’outil fondamental du système de protection, présente l’avantage de rendre aux autorités leur légitimité dans le choix Cette adaptation se traduit aussi par le parti pris d’ajouter de nouveaux final des valeurs opérationnelles des doses pouvant ou non être reçues par volets au système : inclusion de la culture de sûreté dans le processus les professionnels ou les personnes du public. d’optimisation de la protection, implication des parties prenantes dans les prises de décisions importantes pour la protection des humains et de leur Le nouveau système ne mentionne qu’accessoirement l’ancien premier environnement, et protection des espèces non humaines harmonisée avec principe des recommandations 1990, la Justification des pratiques. celle proposée pour les être humains. Ce principe repose sur des considérations d’ordres très variés, social, économique et politique ; le poids des considérations sanitaires est souvent négligeable en comparaison avec les précédentes, parfois inexistant. Il est CONCLUSIONS cependant important de continuer d’y faire référence. Les recommandations 2005, en plus d’un effort évident de clarifications La simplification s’applique aussi aux grandeurs dosimétriques. Aux de la doctrine de protection contre les rayonnements ionisants, présentent trois grandeurs de 1990, dose absorbée, dose équivalente et dose efficace, trois caractéristiques principales qui devraient s’avérer constituer des succèdent la même dose absorbée, qui constitue l’indicateur de gravité avantages notables par rapport à celles de 1990 : (i) elles sont faciles à primaire pour les effets tissulaires (correspondants aux effets déterministes), comprendre et simples à appliquer, (ii) au plan de la pratique quotidienne et la dose efficace, qui constitue l’indicateur de gravité pour les effets et des répercussions sur la conception et l’utilisation des installations, elles

9 A framework for assessing the impact of ionising radiation on non-human species. ICRP Publication 91 (2003). Traduite en français sous le titre : Cadre méthodologique pour évaluer l’impact des rayonnements ionisants sur les espèces non humaines. Publication 91 de la CIPR. (à paraître en 2005)

radio vol30 n4V2.indd 206 3/04/06 16:42:33 système de restriction des doses. Les recommandations 2005 choisissent le stochastiques. La dose équivalente de 1990 ne sert qu’à exprimer le risque concept de contrainte de dose comme niveau fondamental, indépendamment pour un organe ou un tissu particulier ; elle change de nom (provisoirement du type d’exposition et de la situation. Le contrôle s’effectue dorénavant dose pondérée pour les rayonnements), afin de montrer l’usage limité qui sur la dose due à la source d’exposition principale (dominante) et non sur la doit en être fait. dose totale due à l’ensemble des sources. En outre et surtout, la contrainte 2005 a une portée beaucoup plus large que la limite 1990. Elle permet de L’ADAPTATION AU COURANT DE PENSEE MODERNE donne gérer les différentes situations d’exposition à l’aide d’une échelle unique la prédominance à la protection de l’individu, en supposant que, si cette comportant seulement quatre valeurs de contraintes de dose. Ces quatre dernière est performante, la collectivité est protégée à des niveaux de niveaux ne remplacent pas l’ensemble des niveaux de référence, d’action, protection équivalents. Les efforts de protection se focalisent sur la source d’investigation, d’intervention, etc. (actuellement au nombre d’environ de rayonnements affectant l’individu de façon prédominante (source- 25), à l’origine de nombreuses confusions. La nouvelle présentation se related), et non plus sur l’individu affecté par l’ensemble des sources de borne à placer au second plan les anciens niveaux opérationnels mais elle son environnement (individual-related). Il en résulte que les restrictions les situe dans une rationalité globale associée aux situations d’exposition. s’appliquent dorénavant à la source et non à l’individu. Cette approche, Elle présente l’avantage de mettre en évidence le continuum des risques et située à l’opposé de la doctrine passée de la CIPR, devrait conduire leur appréciation en fonction des caractéristiques de l’exposition (maîtrise, elle aussi à une grande simplification des pratiques quotidiennes de la bénéfice individuel, information…). En plus de son intérêt simplificateur, radioprotection. la contrainte, en tant qu’outil fondamental du système de protection, 207 présente l’avantage de rendre aux autorités leur légitimité dans le choix Cette adaptation se traduit aussi par le parti pris d’ajouter de nouveaux final des valeurs opérationnelles des doses pouvant ou non être reçues par volets au système : inclusion de la culture de sûreté dans le processus les professionnels ou les personnes du public. d’optimisation de la protection, implication des parties prenantes dans les prises de décisions importantes pour la protection des humains et de leur Le nouveau système ne mentionne qu’accessoirement l’ancien premier environnement, et protection des espèces non humaines harmonisée avec principe des recommandations 1990, la Justification des pratiques. celle proposée pour les être humains. Ce principe repose sur des considérations d’ordres très variés, social, économique et politique ; le poids des considérations sanitaires est souvent négligeable en comparaison avec les précédentes, parfois inexistant. Il est CONCLUSIONS cependant important de continuer d’y faire référence. Les recommandations 2005, en plus d’un effort évident de clarifications La simplification s’applique aussi aux grandeurs dosimétriques. Aux de la doctrine de protection contre les rayonnements ionisants, présentent trois grandeurs de 1990, dose absorbée, dose équivalente et dose efficace, trois caractéristiques principales qui devraient s’avérer constituer des succèdent la même dose absorbée, qui constitue l’indicateur de gravité avantages notables par rapport à celles de 1990 : (i) elles sont faciles à primaire pour les effets tissulaires (correspondants aux effets déterministes), comprendre et simples à appliquer, (ii) au plan de la pratique quotidienne et la dose efficace, qui constitue l’indicateur de gravité pour les effets et des répercussions sur la conception et l’utilisation des installations, elles

radio vol30 n4V2.indd 207 3/04/06 16:42:33 ne devraient pas nécessiter des adaptations notables ou des changements En résumé, la finalisation du projet de recommandations exige encore importants de comportement de la part des praticiens de la protection, des beaucoup de travail, plus au plan de la présentation et de l’explication qu’à exploitants et des autorités responsables (par exemple, la limite de dose celui de la conception du système proposé. C’est la raison pour laquelle est inchangée), et (iii) elles démontrent la volonté de s’adapter au mode de le document est proposé pour avis à une très large audience, spécialisée pensée et à la culture modernes. dans des secteurs extrêmement variés ; il faut espérer que les observations seront constructives et considérées favorablement par la CIPR. Le privilège accordé maintenant à l’individu par rapport à la collectivité n’apportera rien de particulièrement nouveau du point de vue opérationnel. Un dernier point peut paraître critiquable : c’est la partie modeste qui est Il officialise le changement progressif de comportement sociétal vis-à-vis dévolue au domaine médical (10 paragraphes sur 251). Dans les années des risques de la vie. Son intérêt ne réside sans doute pas dans le choix 60 et suivantes, qui ont vu le développement de l’industrie nucléaire, la délibéré de la prédominance de l’individu sur la collectivité, mais sur CIPR s’est logiquement focalisée de façon prédominante sur le domaine certaines restrictions pratiques, qui devraient s’ensuivre ipso facto, comme industriel et les situations accidentelles. Aujourd’hui il peut paraître celle de l’usage abusif de la dose collective, source d’interprétations curieux que ses nouvelles recommandations n’accordent qu’une place souvent erronées. extrêmement réduite à la protection en médecine. Cette réserve ne doit pas être interprétée comme un message selon lequel les problèmes qui relèvent Le projet tel qu’il est présenté actuellement constitue en fait une du domaine médical seraient actuellement résolus ; cette assertion serait 208 actualisation des recommandations 1990. En raison de sa concision, il ne en contradiction avec l’attitude présente de la CIPR, qui montre depuis les peut être compris et assimilé que par des lecteurs qui possèdent une culture années 90 son intérêt croissant pour les problèmes médicaux, comme le solide et approfondie de la radioprotection moderne. Les recommandations prouvent les très nombreuses publications récentes qui lui sont consacrées 1990 comportaient des volets explicatifs et pédagogiques détaillés, qui font (depuis 1996 avec la Publication 73 sur la protection en médecine, sept défaut dans ce projet. Ces aspects seront développés dans des «documents publications traitent de questions pratiques et quatre autres sont à paraître fondateurs» en cours d’élaboration et qui seront publiés en même temps prochainement). Les raisons en sont plutôt à rechercher dans le fait que le que les nouvelles recommandations générales. C’est pour permettre la concept de contrainte, mis en avant dans les nouvelles recommandations, publication concomitante de tous ces documents que celle-ci est retardée à n’est pas très approprié pour la protection du patient. Il convient cependant 2006 (voire début 2007). Au stade actuel, certaines rubriques des nouvelles de noter que, dans le cadre de la rencontre entre la Commission principale recommandations, particulièrement celles qui traitent de nouveautés, de la CIPR et les professionnels de la radioprotection organisée par la devraient être développées et étayées par une argumentation solide ; SFRP en marge de la réunion de la Commission principale en mars 2005 d’autres sont difficiles à comprendre et apparaissent parfois contradictoires. à Paris, le président de la CIPR, en réponse aux remarques du GT SFRP/ Il paraîtrait normal, par exemple, d’expliquer pourquoi la CIPR accorde CIPR10, a indiqué que cette question sera examinée avec attention avant la une place plus réduite au principe de Justification des pratiques, de montrer publication des nouvelles recommandations. clairement la différence entre les contraintes 2005 et 1990, de préciser les significations et utilisations respectives de la contrainte et de la limite, de développer le concept d’exclusion et d’en justifier le niveau, etc.

radio vol30 n4V2.indd 208 3/04/06 16:42:34 ne devraient pas nécessiter des adaptations notables ou des changements En résumé, la finalisation du projet de recommandations exige encore importants de comportement de la part des praticiens de la protection, des beaucoup de travail, plus au plan de la présentation et de l’explication qu’à exploitants et des autorités responsables (par exemple, la limite de dose celui de la conception du système proposé. C’est la raison pour laquelle est inchangée), et (iii) elles démontrent la volonté de s’adapter au mode de le document est proposé pour avis à une très large audience, spécialisée pensée et à la culture modernes. dans des secteurs extrêmement variés ; il faut espérer que les observations seront constructives et considérées favorablement par la CIPR. Le privilège accordé maintenant à l’individu par rapport à la collectivité n’apportera rien de particulièrement nouveau du point de vue opérationnel. Un dernier point peut paraître critiquable : c’est la partie modeste qui est Il officialise le changement progressif de comportement sociétal vis-à-vis dévolue au domaine médical (10 paragraphes sur 251). Dans les années des risques de la vie. Son intérêt ne réside sans doute pas dans le choix 60 et suivantes, qui ont vu le développement de l’industrie nucléaire, la délibéré de la prédominance de l’individu sur la collectivité, mais sur CIPR s’est logiquement focalisée de façon prédominante sur le domaine certaines restrictions pratiques, qui devraient s’ensuivre ipso facto, comme industriel et les situations accidentelles. Aujourd’hui il peut paraître celle de l’usage abusif de la dose collective, source d’interprétations curieux que ses nouvelles recommandations n’accordent qu’une place souvent erronées. extrêmement réduite à la protection en médecine. Cette réserve ne doit pas être interprétée comme un message selon lequel les problèmes qui relèvent Le projet tel qu’il est présenté actuellement constitue en fait une du domaine médical seraient actuellement résolus ; cette assertion serait actualisation des recommandations 1990. En raison de sa concision, il ne en contradiction avec l’attitude présente de la CIPR, qui montre depuis les 209 peut être compris et assimilé que par des lecteurs qui possèdent une culture années 90 son intérêt croissant pour les problèmes médicaux, comme le solide et approfondie de la radioprotection moderne. Les recommandations prouvent les très nombreuses publications récentes qui lui sont consacrées 1990 comportaient des volets explicatifs et pédagogiques détaillés, qui font (depuis 1996 avec la Publication 73 sur la protection en médecine, sept défaut dans ce projet. Ces aspects seront développés dans des «documents publications traitent de questions pratiques et quatre autres sont à paraître fondateurs» en cours d’élaboration et qui seront publiés en même temps prochainement). Les raisons en sont plutôt à rechercher dans le fait que le que les nouvelles recommandations générales. C’est pour permettre la concept de contrainte, mis en avant dans les nouvelles recommandations, publication concomitante de tous ces documents que celle-ci est retardée à n’est pas très approprié pour la protection du patient. Il convient cependant 2006 (voire début 2007). Au stade actuel, certaines rubriques des nouvelles de noter que, dans le cadre de la rencontre entre la Commission principale recommandations, particulièrement celles qui traitent de nouveautés, de la CIPR et les professionnels de la radioprotection organisée par la devraient être développées et étayées par une argumentation solide ; SFRP en marge de la réunion de la Commission principale en mars 2005 d’autres sont difficiles à comprendre et apparaissent parfois contradictoires. à Paris, le président de la CIPR, en réponse aux remarques du GT SFRP/ Il paraîtrait normal, par exemple, d’expliquer pourquoi la CIPR accorde CIPR10, a indiqué que cette question sera examinée avec attention avant la une place plus réduite au principe de Justification des pratiques, de montrer publication des nouvelles recommandations. clairement la différence entre les contraintes 2005 et 1990, de préciser les significations et utilisations respectives de la contrainte et de la limite, de développer le concept d’exclusion et d’en justifier le niveau, etc.

radio vol30 n4V2.indd 209 3/04/06 16:42:35 Abstract Annales de l’Association belge de Radioprotection, Vol.30, n°4, 2005

The recommendations of the ICRP: the reasons for a change THE IN VIVO MEASUREMENTS OF RADIOACTIVE BODY BURDENS: Since its foundation in 1928, the International Commission on Radiological Protection (ICRP) has regularly produced recommendations on the TECHNIQUES AND PRACTICES protection against ionising radiation; these recommendations are currently taken up by international organisations and by states. Since 1990, date JL Genicot of issue of the most recent recommendations (Publication 60), advances SCK*CEN Boeretang 200, B-2400 Mol Belgium in scientific knowledge, technical developments, feedback and desire to meet modern societal feelings, have incited the ICRP to modify deeply its Text presented at the Training Course on Internal Dosimetry, IRMM-Geel, June 06, system of protection. The latest draft, which was recently presented openly 2006 for consultation and proposals, is described and discussed.

Key words: ICRP / recommendations / radiological protection / constraints Summary 210 The in vivo assessment of radioactive body burdens has been developed for more than sixty years, always using the latest achievements in terms of technical possibilities. If the first systematic approach allowed in 1931 the detection of 226Ra with a detection limit of 185 kBq, the effect of the geometry and of the background on the results were immediately pointed out. The measurement techniques now are able to quantify and localise radioactive burdens in the body with detection limits as low as 100 Bq 226Ra and less than 5 Bq for 137Cs..

The purpose of this course is to describe the different techniques employed to quantify the radioactive body burdens of fission and activation products, encountered in the nuclear energy industry, radionuclides used in the nuclear medicine and some of the naturally occurring radioactive materials found in the non nuclear industries. The techniques are compared and the state of the art in this field is described. Lots of examples are commented on the points of view of the feasibility, the best technique and the expected results.

10 Principales remarques du GT SFRP/CIPR concernant le projet de recommandations 2005 de la CIPR, revue Radioprotection, Vol 40, N°1, Janvier-Mars 2005, p. 89

radio vol30 n4V2.indd 210 3/04/06 16:42:35 Abstract Annales de l’Association belge de Radioprotection, Vol.30, n°4, 2005

The recommendations of the ICRP: the reasons for a change THE IN VIVO MEASUREMENTS OF RADIOACTIVE BODY BURDENS: Since its foundation in 1928, the International Commission on Radiological Protection (ICRP) has regularly produced recommendations on the TECHNIQUES AND PRACTICES protection against ionising radiation; these recommendations are currently taken up by international organisations and by states. Since 1990, date JL Genicot of issue of the most recent recommendations (Publication 60), advances SCK*CEN Boeretang 200, B-2400 Mol Belgium in scientific knowledge, technical developments, feedback and desire to meet modern societal feelings, have incited the ICRP to modify deeply its Text presented at the Training Course on Internal Dosimetry, IRMM-Geel, June 06, system of protection. The latest draft, which was recently presented openly 2006 for consultation and proposals, is described and discussed.

Key words: ICRP / recommendations / radiological protection / constraints Summary 211 The in vivo assessment of radioactive body burdens has been developed for more than sixty years, always using the latest achievements in terms of technical possibilities. If the first systematic approach allowed in 1931 the detection of 226Ra with a detection limit of 185 kBq, the effect of the geometry and of the background on the results were immediately pointed out. The measurement techniques now are able to quantify and localise radioactive burdens in the body with detection limits as low as 100 Bq 226Ra and less than 5 Bq for 137Cs..

The purpose of this course is to describe the different techniques employed to quantify the radioactive body burdens of fission and activation products, encountered in the nuclear energy industry, radionuclides used in the nuclear medicine and some of the naturally occurring radioactive materials found in the non nuclear industries. The techniques are compared and the state of the art in this field is described. Lots of examples are commented on the points of view of the feasibility, the best technique and the expected results.

radio vol30 n4V2.indd 211 3/04/06 16:42:36 INTRODUCTION The problem of Radiation Protection is a problem of comparison: Radiation exists in nature and delivers doses to the body. These doses can The objective of this course is to provide guidance on the direct be due to natural sources or to medical intervention (by X-rays, by CT- detection and quantification of a body burden for those involved in scanner, etc…). This dose vary from an individual to another. The mean occupational monitoring of workers potentially exposed to internal annual dose is evaluated to 3.75 mSv/year (world mean) and to 4.5 mSv/ contamination by radionuclides. Different techniques are available and the year for the Belgian mean (Figure 1) (51% natural, 49% artificial). choice must be conducted by different parameters. The human body, as every living cell, also contains radioactive species. The total activity in a human body (not coming from a contamination NEEDS FOR INTERNAL CONTAMINATION MEASUREMENTS accident) vary between 4000 and 10000 Bq (Figure 2, Table 1). 40K, 14C and 87Rb are the radionuclides the most present in the tissues. This natural The purpose of In Vivo Counting is to assist those responsible activity can lead to doses that represents about 7% of the total annual for operating a radiation protection program in the protection of workers dose as shown in Figure 1. potentially exposed to internal contamination by radioactive materials. It is part of a general program whose goal is to monitor the total annual It is important to know which radionuclides are to be investigated dose of a worker exposed to ionizing radiation and to reduce the eventual (separate natural and occupational contaminations) in each type of committed dose. measurement. The first step is to defined if the contamination is external (cloths, skin or Figure 3 shows the position of the direct measurement in the Radiation hair) or internal. If the contamination is internal, it is necessary to know protection organisation. if the contaminant is introduced by inhalation, ingestion (intake) or via a wound (uptake). The second step will be to assess the amount of incorporated activity: three types of examinations can be performed to make this assessment:

1. Environmental methods: Measurement of air samples and assessment of intake based on breathing rate estimates. 2. Indirect methods: Analysis of excreta: urine, faeces, nose blows, sweat, nails or hair etc. 3. Direct Methods: Whole Body Counting (WBC) or Organ Burden Counting, consisting of the measurement of electromagnetic radiation (X-rays and γ-rays) emanating from the body.

radio vol30 n4V2.indd 212 3/04/06 16:42:36 INTRODUCTION The problem of Radiation Protection is a problem of comparison: Radiation exists in nature and delivers doses to the body. These doses can The objective of this course is to provide guidance on the direct be due to natural sources or to medical intervention (by X-rays, by CT- detection and quantification of a body burden for those involved in scanner, etc…). This dose vary from an individual to another. The mean occupational monitoring of workers potentially exposed to internal annual dose is evaluated to 3.75 mSv/year (world mean) and to 4.5 mSv/ contamination by radionuclides. Different techniques are available and the year for the Belgian mean (Figure 1) (51% natural, 49% artificial). choice must be conducted by different parameters. The human body, as every living cell, also contains radioactive species. The total activity in a human body (not coming from a contamination NEEDS FOR INTERNAL CONTAMINATION MEASUREMENTS accident) vary between 4000 and 10000 Bq (Figure 2, Table 1). 40K, 14C and 87Rb are the radionuclides the most present in the tissues. This natural The purpose of In Vivo Counting is to assist those responsible activity can lead to doses that represents about 7% of the total annual for operating a radiation protection program in the protection of workers dose as shown in Figure 1. potentially exposed to internal contamination by radioactive materials. It is part of a general program whose goal is to monitor the total annual It is important to know which radionuclides are to be investigated dose of a worker exposed to ionizing radiation and to reduce the eventual (separate natural and occupational contaminations) in each type of committed dose. measurement. 213 The first step is to defined if the contamination is external (cloths, skin or Figure 3 shows the position of the direct measurement in the Radiation hair) or internal. If the contamination is internal, it is necessary to know protection organisation. if the contaminant is introduced by inhalation, ingestion (intake) or via a wound (uptake). The second step will be to assess the amount of incorporated activity: three types of examinations can be performed to make this assessment:

1. Environmental methods: Measurement of air samples and assessment of intake based on breathing rate estimates. 2. Indirect methods: Analysis of excreta: urine, faeces, nose blows, sweat, nails or hair etc. 3. Direct Methods: Whole Body Counting (WBC) or Organ Burden Counting, consisting of the measurement of electromagnetic radiation (X-rays and γ-rays) emanating from the body.

radio vol30 n4V2.indd 213 3/04/06 16:42:37 6

Cosmic Rays Medical 7% Applications Radon 48% 25%

Thoron 2% Nuclear Energy & Weapons Soil and Buildings 1% 10% R.A. in the body 7%

Figure 1: Radiative doses delivered to the Belgian population

U(1) Th(0.1) Ra226(1.1) Cs- 137(20) Rb-87(450) H-3(20…40) K-40(3000-6000)

C-14(3700)

Pb-210(40)

6 Figure 2: Radioactive body burden of a human being

Radionuclide 7 Amount in Bq Cosmic Rays U 1 Th 0.11 Medical 7% Ra-226 1.1 Applications Radon K-40 3000...5000 48% 25% Po-210 40 C-14 3700 H-3 20.....40 Rb-87 450 Thoron Cs-137 910 (1964) 2% 250 (1987) Nuclear Energy & 25 (in 1997) Weapons Soil and Buildings Total 4000.... 10000 Bq 1% 10% Table 1: Radionuclides in the body (for Belgian population). R.A. in the body 7%

Figure 1: Radiative doses delivered to the Belgian population 214 Direct measurements IndirectIndirect (In vivo) measurementsmeasurements (In (In vitro)vitro) U(1) Th(0.1) Ra226(1.1) Cs- 137(20) Excretion Rate, M m(t) Rb-87(450) Burden in m(t) Assessed H-3(20…40) Body/organ, M Intake Concentration in K-40(3000-6000) the air DAC-hr

C-14(3700) DoseDose e(g)j RateRate

Pb-210(40) Committed Effective Dose (Sv)

Figure 3: Position of Internal Dosimetry in Radiation Protection Figure 2: Radioactive body burden of a human being

Radionuclide Amount in Bq

radio vol30 n4V2.indd 214 3/04/06 16:42:39 6

Cosmic Rays Medical 7% Applications Radon 48% 25%

Thoron 2% Nuclear Energy & Weapons Soil and Buildings 1% 10% R.A. in the body 7%

Figure 1: Radiative doses delivered to the Belgian population

U(1) Th(0.1) Ra226(1.1) Cs- 137(20) Rb-87(450) H-3(20…40) K-40(3000-6000)

C-14(3700)

Pb-210(40)

Figure 2: Radioactive body burden of a human being

Radionuclide 7 Amount in Bq U 1 Th 0.11 Ra-226 1.1 K-40 3000...5000 Po-210 40 C-14 3700 H-3 20.....40 Rb-87 450 Cs-137 910 (1964) 250 (1987) 25 (in 1997) Total 4000.... 10000 Bq

Table 1: Radionuclides in the body (for Belgian population).

215 Direct measurements IndirectIndirect (In vivo) measurementsmeasurements (In (In vitro)vitro)

Excretion Rate, M m(t) Burden in m(t) Assessed Body/organ, M Intake Concentration in the air DAC-hr

DoseDose e(g)j RateRate

Committed Effective Dose (Sv)

Figure 3: Position of Internal Dosimetry in Radiation Protection

radio vol30 n4V2.indd 215 3/04/06 16:42:40 BASIC PRINCIPLES AND PROCEDURES FOR THE Its design is based by considering three types of interactions of MEASUREMENTS electromagnetic radiation with matter:

The direct measurement of internal radioactive contamination is • Photo-electric effect (proportional to Zn, where Z is the based on the detection of radiations emitted by the contaminant and that atomic number (4

Each of these points will be examined separately.

The shielded room

It is used to reduce the natural and artificial environmental radiation (the background). In this room, the counting can be performed on the person either in a sitting position (tilted chair technique) or in a supine (or prone) position on a flat bed (Figure 4). Fig. 4: Tilted chair geometry and bed geometry for In Vivo counting of radioactive body burdens

radio vol30 n4V2.indd 216 3/04/06 16:42:40 BASIC PRINCIPLES AND PROCEDURES FOR THE Its design is based by considering three types of interactions of MEASUREMENTS electromagnetic radiation with matter:

The direct measurement of internal radioactive contamination is • Photo-electric effect (proportional to Zn, where Z is the based on the detection of radiations emitted by the contaminant and that atomic number (4

Each of these points will be examined separately.

The shielded room b) Bed Geometry

It is used to reduce the natural and artificial environmental radiation (theb) Bed Geometry background). In this room, the counting can be performed on the person Fig. 4: Tilted chair geometry and bed geometry for In Vivo counting of radioactive body burdens either in a sitting position (tilted chair technique) or in a supine (or prone) position on a flat bed (Figure 4). Fig. 4: Tilted chair geometry and bed geometry Fig.for In 4: Vivo Tilted Figure counting chair 5 shows of geometry radioactive how primary and body cosmic bed burdens geometryinteracts wi thfor the In atmosphere Vivo counting and the ofmaterials of the radioactiveshielding where body it burdens produces �-rays of 511 keV by the annihilation process of positrons and negatons. Neutrons also are produced during spallation reactions. Figure 5 shows how primary cosmic interacts with the atmosphere and the materials of the shielding where it produces �-rays of 511 keV by the annihilation process of positrons and negatons. Neutrons also are produced during spallation reactions.

radio vol30 n4V2.indd 217 3/04/06 16:42:43

Fig. 5: Origin of natural and artificial radiation background.

Fig. 5: Origin of natural and artificial radiation background. 9

a) Tilted chair

b) Bed Geometry

Fig. 4: Tilted chair geometry and bed geometry for In Vivo counting of radioactive body burdens Figure 5 shows how primary cosmic interacts with the atmosphere Figure 7 presents the comparison of the backgrounds outside and inside and the Figurematerials 5 shows of how the primaryshielding cosmic where interacts it produces with the atmosphere γ-rays of and 511 the keV materials of the the room #1. This room produces a reduction of about two decades in byshielding the annihilation where it produces process �-rays of of positrons 511 keV by and the annihilatio negatons.n process Neutrons of positrons also are and negatons. the continuum (in terms of count rate in the energy range 200 keV-2000 producedNeutrons alsoduring are producedspallation during reactions. spallation reactions. keV).

218 10 The laboratory for WBC of the SCK�CEN in Mol is equipped with five shielded rooms. Each room is designed with a different materials to respond to comparison tests in a Fig. 5: Origin of natural and artificial radiation background. R&D program. Figure 6 shows the external view of the rooms 3,4 and 5.

The laboratory for WBC of the SCK•CEN in Mol is equipped with five The shielding is based on the shift of the gamma-rays towards the low 10 shielded rooms. Each room is designed with a different materials to respond energies. In the low energy range (less than 60 keV), a shielding can be The laboratory for WBC of the SCK�CEN in Mol is equipped with five shielded rooms. Each roomto comparisonis designed with atests different in mate a R&Drials to respond program. to comparison Figure tests 6 showsin a the external view useless and even aggravating by increase the continuum. A ventilation R&D program.of the Figure rooms 6 shows 3,4 theand exte 5.rnal view of the rooms 3,4 and 5. system must be used for hygienic and comfort reasons inside these small 7 rooms. This air is filtered to remove contaminated dust particles ( Be - T½= 53.28 days - a spallation product of cosmic rays with 14N and with 16O of 214 214 the air), radon daughters ( Pb, T½ = 27 min. and Bi, T½ = 19.9 min.) and radioactive fall-out.

Fig. 6: Laboratory complex for the WBC of the SCK�CEN. Fig. 6: Laboratory complex for the WBC of the SCK�CEN.

Figure 7 Figurepresents 7 presents the comparison the comparison ofof thethe backgrounds backgrounds outside outside and inside and the roominside #1. the This room room #1. This room producesradioproduces a vol30 reduction n4V2.indd a reduction of 218 about of about two two decades in thein thecontinuum continuum (in terms (in of count terms rate of in countthe energy rate in the energy 3/04/06 16:42:46 range 200range keV-2000 200 keV-2000 keV). keV).

1000000 1000000 Outside the room 100000 Outside the room

10000010000

Inside the room 1000 10000

Number of counts per Channel per counts of Number 100 Inside the room 0 500 1000 1500 2000 1000 Photon Energy (keV)

Number of counts per Channel per counts of Number Fig. 1007: Comparison of the background outside and inside a shielded room (room NR 1 0in figure 4.2 – 60000500 s counting time1000 with 8”x4” Na(Tl)1500 detector). 2000 Photon Energy (keV)

Fig. 7: Comparison of the background outside and inside a shielded room (room NR 1 in figure 4.2 – 60000 s counting time with 8”x4” Na(Tl) detector). 10 The laboratory for WBC of the SCK�CEN in Mol is equipped with five shielded rooms. Each room is designed with a different materials to respond to comparison tests in a R&D program. Figure 6 shows the external view of the rooms 3,4 and 5.

Figure 5 shows how primary cosmic interacts with the atmosphere FigureFig. 7 6: presents Laboratory the complex comparison for the WBCof the of backgroundsthe SCK�CEN. outside and inside and the materials of the shielding where it produces γ-rays of 511 keV the room #1. This room produces a reduction of about two decades in Figure 7 presents the comparison of the backgrounds outside and inside the room #1. This room by the annihilation process of positrons and negatons. Neutrons also are produces a reductionthe continuum of about two(in decadesterms ofin thecount continuum rate in (in the terms energy of count range rate 200in the keV-2000 energy produced during spallation reactions. range 200 keV-2000keV). keV).

1000000 Outside the room

100000

10000

Inside the room 1000

Number of counts per Channel per counts of Number 100 0 500 1000 1500 2000 Photon Energy (keV) 219

Fig. 7: Comparison of the background outside and inside a shielded room (room NR 1 in figure 4.2 – 60000 s counting time with 8”x4” Na(Tl) detector).

The laboratory for WBC of the SCK•CEN in Mol is equipped with five The shielding is based on the shift of the gamma-rays towards the low shielded rooms. Each room is designed with a different materials to respond energies. In the low energy range (less than 60 keV), a shielding can be to comparison tests in a R&D program. Figure 6 shows the external view useless and even aggravating by increase the continuum. A ventilation of the rooms 3,4 and 5. system must be used for hygienic and comfort reasons inside these small 7 rooms. This air is filtered to remove contaminated dust particles ( Be - T½= 53.28 days - a spallation product of cosmic rays with 14N and with 16O of 214 214 the air), radon daughters ( Pb, T½ = 27 min. and Bi, T½ = 19.9 min.) and radioactive fall-out.

radio vol30 n4V2.indd 219 3/04/06 16:42:47 The detectors Radiation used for in vivo counting

At the beginning of the In Vivo measurements (1931), quartz electrometers and ionizing chambers were used, mainly to quantify 226Ra in the body with detection limits of 200 kBq. The Geiger-Müler tube was first use by Evans also to measure the 226Ra with an LD of 4000 Bq. The proportional counter is introduced by Taylor & Rundo in 1962 to measure the low energy photons emerging from the lungs. Afterwards, the scintillators (liquid, plastic and crystal) and semiconductors detectors were introduced in the technique of in-Vivo counting from 1970. Scintillator detectors

Different types of detectors are commercially available for in Sodium iodide and bismuth germanate are the most popular scintillators vivo counting. The choice of detector is based on three criteria: the type of used today for in vivo counting. Plastic and liquid scintillation detectors radiation, the required detection limit and the energy range. Psychological are sometimes used in WBC when the resolution is less important than the and financial constrains are parameters that also affect the choice of detector. counting rate. 220 They can work in three different modes: gross counting, spectrometric and scanning. Thallium activated Sodium Iodide crystal: NaI(Tl) The detectors for in vivo counting are subdivided into three categories: - gas detectors, The scintillation detector became really useful with the invention - scintillation detectors, in 1948 of thallium activated sodium iodide (3% molar concentration). - semi-conductor detectors. This crystal can be manufactured with very large dimensions and is easy to use. A γ-photon absorbed in the scintillation medium causes the ionisation Gas detector: of the material. The ionisation is converted into blue and ultra-violet light through a de-excitation process. The light diffuses through the crystal The proportional counter, used for the measurement of low and on to the material surrounding the scintillator (a coating of MgO,

energy photon emitters in the lungs is shown in Fig. 8, in its measurement Al2O3 or TiO2 powder). The light pulse passes from the crystal through a position. It is designed to reduce the background by using anti-coincidence quartz window that is optically coupled to one or several photomultipliers chambers and with a special electronic circuit for the pulse shape. collecting the weak light pulses with a maximum intensity at 415 nm (see Fig. 9).

radio vol30 n4V2.indd 220 3/04/06 16:42:48 11 The shielding is based on the shift of the gamma-rays towards the low energies. In the low energy range (less than 60 keV), a shielding can be useless and even aggravating by increase the continuum. A ventilation system must be used for hygienic and comfort reasons inside these small 7 rooms. This air is filtered to remove contaminated dust particles ( Be - T½= 53.28 days - a spallation 14 16 214 product of cosmic rays with N and with O of the air), radon daughters ( Pb, T½ = 27 min. and 214 Bi, T½ = 19.9 min.) and radioactive fall-out.

The detectors Radiation used for in vivo counting

At the beginning of the In Vivo measurements (1931), quartz electrometers and ionizing chambers were used, mainly to quantify 226Ra in the body with detection limits of 200 kBq. The Geiger-Müler tube was first use by Evans also to measure the 226Ra with an LD of 4000 Bq. The proportional counter is introduced by Taylor & Rundo in 1962 to measure the low energy photons emerging fro the lungs. Afterwards, the scintillators (liquid, plastic and crystal) and semiconductors detectors were introduced in the technique of in-Vivo counting from 1970.

Different types of detectors are commercially available for in vivo counting. The choice of detector is based on three criteria: the type of radiation, the required detection limit and the energy range. Psychological and financial constrains are parameters that also affect the choice of detector. They can work in three different modes: gross counting, spectrometric and scanning.

The detectors for in vivo counting are subdivided into three categories: - gas detectors, - scintillation detectors, - semi-conductor detectors.

Gas detector:

The proportional counter, used for the measurement of low energy photon emitters in the lungs is shown in Fig. 8, in its measurement position. It is designed to reduce the background by using anti-coincidence chambers and with a special electronic circuit for the pulse shape.

The detectors Radiation used for in vivo counting

At the beginning of the In Vivo measurements (1931), quartz electrometers and ionizing chambers were used, mainly to quantify 226Ra in the body with detection limits of 200 kBq. The Geiger-Müler tube was first use by Evans also to measure the 226Ra with an LD of 4000 Bq. The proportional counter is introduced by Taylor & Rundo in 1962 to measure the low energy photons emerging from the lungs. Afterwards, the scintillators (liquid, plastic and crystal) and Fig. 8: Paired proportional counter for the measurement of plutonium in the lungs. semiconductors detectors were introduced in the technique of in-Vivo Scintillator detectors counting from 1970. Scintillator detectors

Different types of detectors are commercially available for in Sodium iodide and bismuth germanate are the most popular scintillators vivo counting. The choice of detector is based on three criteria: the type of used today for in vivo counting. Plastic and liquid scintillation detectors radiation, the required detection limit and the energy range. Psychological are sometimes used in WBC when the resolution is less important than the and financial constrains are parameters that also affect the choice of detector. counting rate. They can work in three different modes: gross counting, spectrometric and 221 scanning. Thallium activated Sodium Iodide crystal: NaI(Tl) The detectors for in vivo counting are subdivided into three categories: - gas detectors, The scintillation detector became really useful with the invention - scintillation detectors, in 1948 of thallium activated sodium iodide (3% molar concentration). - semi-conductor detectors. This crystal can be manufactured with very large dimensions and is easy to use. A γ-photon absorbed in the scintillation medium causes the ionisation Gas detector: of the material. The ionisation is converted into blue and ultra-violet light through a de-excitation process. The light diffuses through the crystal The proportional counter, used for the measurement of low and on to the material surrounding the scintillator (a coating of MgO, energy photon emitters in the lungs is shown in Fig. 8, in its measurement Al2O3 or TiO2 powder). The light pulse passes from the crystal through a position. It is designed to reduce the background by using anti-coincidence quartz window that is optically coupled to one or several photomultipliers chambers and with a special electronic circuit for the pulse shape. collecting the weak light pulses with a maximum intensity at 415 nm (see Fig. 9).

radio vol30 n4V2.indd 221 3/04/06 16:42:49 12

Sodium iodide and bismuth germanate are the most popular scintillators used today for in vivo counting. Plastic and liquid scintillation detectors are sometimes used in WBC when the resolution is less important than the counting rate.

Thallium activated Sodium Iodide crystal: NaI(Tl)

The scintillation detector became really useful with the invention in 1948 of thallium activated sodium iodide (3% molar concentration). This crystal can be manufactured with very large dimensions and is easy to use. A �-photon absorbed in the scintillation medium causes the ionisation of the material. The ionisation is converted into blue and ultra-violet light through a de-excitation process. The light diffuses through the crystal and on to the material surrounding the scintillator (a coating of MgO, Al2O3 or TiO2 powder). The light pulse passes from the crystal through a quartz window that is optically coupled to one or several photomultipliers collecting the weak light pulses with a maximum intensity at 415 nm (see Fig. 9).

The phoswich detector H.V. Diffuser The phoswich detector consists of a thin NaI(Tl) crystal optically coupled to a CsI(Tl) crystal. Both are optically coupled to a common photomultiplier NaI(Tl) (Fig.10). The two scintillators are characterised by different decay constants crystal discriminated by a pulse shape analyser.

Fig. 9: Schematic of mounting of a Scintillation Counter A NaI(Tl) detector can make very sensitive measurements in relatively A NaI(Tl) detectorshort times. can make It has very also sensitive several measur disadvantages:ements in relatively short times. It has also several disadvantages:1. fairly poor resolution (7% at 1.46 MeV of 40K). 1. fairly poor resolution (7% at 1.46 MeV of 40K). 2. Sodium iodide is hygroscopic. But hydrated crystal can be 2. Sodium iodide is hygroscopic. But hydrated crystal can be repaired. 3. The silicone greaserepaired. used as optical contact can age . 2224. Fast temperature3. The changes silicone can grease crack the used crystal. as optical contact can age . Semi-conductor detectors 4. Fast temperature changes can crack the crystal. NaI(Tl) has been the best choice for fast and accurate measurements for the assessment of body burdens of � -emitting materials (WBC) for more than 40 years. In 1962, it was discovered that a semi-conductor crystal would NaI(Tl) has been the best choice for fast and accurate measurements for generate an electric charge on the electrodes of a reverse polarized diode the assessment of body burdens of γ-emitting materials (WBC) for more when an X- or γ-ray photon was absorbed in the intrinsic zone. The crystal Other inorganic and organic scintillation detectors than 40 years. (at that time a germanium or a silicon) is doped with lithium to reduce the

CsI(Tl) and Bismuth germanate (Bi4Ge3O12 - commonly known as BGO) are good inorganic leakage current due to the impurities of the crystal: a photon absorbed in scintillation detectors. CsI(Tl) is generally associated with a NaI(Tl) crystal in special devices (see the depleted zone of a reverse biased diode generates electron-hole pairs below) but can also be used Otheralone if inorganic the light is and collected organic with scintillation silicon photodiodes detectors instead of photomultipliers. Finally, organic scintillation detectors (plastic or liquid) are characterised by a and the electric charges are collected at the electrodes (Fig. 11):

CsI(Tl) and Bismuth germanate (Bi4Ge3O12 - commonly known as BGO) are good inorganic scintillation detectors. CsI(Tl) is generally associated with a NaI(Tl) crystal in special devices (see below) but can also be used alone if the light is collected with silicon photodiodes instead of photomultipliers. Finally, organic scintillation detectors (plastic or liquid) are characterised by a poor resolution (due to the low Z) and a high efficiency, as they can be used in very large volumes.

radio vol30 n4V2.indd 222 3/04/06 16:42:51 13 13 poor resolution (due to the low The Z) andphoswich a high efficien detectorcy, as they can be used in very large volumes. poor resolution (due13 to the low Z) and a high efficiency, as they can be used in very large volumes. poor resolution (dueThe tophoswich the low Z) detector and a high consists efficien cy,of aas thin they NaI(Tl) can be used crystal in very optically large volumes. coupled to The phoswich detector a CsI(Tl) crystal. Both The are phoswich optically detector coupled to a common photomultiplier The phoswich detector consists of a thin NaI(Tl) crystal optically coupled to a CsI(Tl) crystal. Both The(Fig.10). phoswich ThedetectorThe two phoswich scintillators detector are consists characterised of a thin NaI(Tl) by different crystal optically decay constants coupled to a CsI(Tl) crystal. Both they are optically coupled to a common photomultiplier (Fig.10). The two scintillators are discriminatedthey by are a opticallypulse shape coupled analyser. to a common photomultiplier (Fig.10). The two scintillators are characterised by different decay constants discriminated by a pulse shape analyser. The phoswich detector consistscharacterised of a thin NaI(Tl) by different crystal decay optically constants coupled discriminated to a CsI(Tl) crystal. by a pulse Both shape analyser. they are optically coupled to a common photomultiplier (Fig.10). The two scintillators are characterised by different decay constants discriminated by a pulse shape analyser.

A NaI(Tl) detector can make very sensitive measurements in relatively short times. It has also several disadvantages: 1. fairly poor resolution (7% at 1.46 MeV of 40K). 2. Sodium iodide is hygroscopic. But hydrated crystal can be Fig. 10: Phoswich detector and its electronics repaired. Fig. 10: Phoswich detector and its electronics

3. The silicone grease used as optical contact can age . Semi-conductorFig. 10: Phoswich detectors detector and its electronics 223 Semi-conductor detectors 4. Fast temperature changes can crack the crystal. Semi-conductor detectors

In 1962, it was discovered In 1962, that it was a semi-conductor discovered crystal that would a semi-conductor generate an electric crystal charge would on Semi-conductor detectors In 1962, it was discovered that a semi-conductor crystal would generate an electric charge on the electrodes of a reverse polarized diode when an X- or �-ray photon was absorbed in the intrinsic NaI(Tl) has been the best choice for fast and accurate measurements for generate anthe electric electrodes charge of a reverse on the polarized electrodes diode ofwhen a reverse an X- or �polarized-ray photon diode was absorbed in the intrinsic zone. The crystal (at that time a germanium or a silicon) is doped with lithium to reduce the leakage the assessment of body burdens of γ-emitting materials (WBC) for more In 1962, whenit was discoveredan X-zone. or that The-ray a crystalsemi-conductor photon (at wasthat time absorbed crystal a germanium would in thegenerate or intrinsic a silicon) an electric zone. is doped charge The with oncrystal lithium to reduce the leakage current due to the impurities ofγ the crystal: a photon absorbed in the depleted zone of a reverse the electrodes of a reverse polarizedcurrent diodedue to when the impurities an X- or �-ray of the photon crystal: was a absorbed photon absorbed in the intrinsic in the depleted zone of a reverse than 40 years. biased diode (atgenerates that time electron-hol a germaniume pairs and or thea silicon) electric chargesis doped are with collected lithium at the to electrodes reduce the zone. The crystal (at that timebiased a germanium diode generates or a silicon) electron-hol is doped withe pairs lithium and the to reduceelectric the charges leakage are collected at the electrodes (Fig. 11): current due to theleakage impurities current(Fig. of the 11): due crystal: to the a phot impuritieson absorbed of inthe the crystal: depleted a zonephoton of a absorbedreverse in biased diode generatesthe depleted electron-hol zonee pairsof a andreverse the electric biased charges diode are generates collected atelectron-hole the electrodes pairs Other inorganic and organic scintillation detectors (Fig. 11): and the electric charges are collected at the electrodes (Fig. 11):

CsI(Tl) and Bismuth germanate (Bi4Ge3O12 - commonly known as BGO) are good inorganic scintillation detectors. CsI(Tl) is generally associated with a NaI(Tl) crystal in special devices (see below) but can also be used alone if the light is collected with silicon photodiodes instead of photomultipliers. Finally, organic scintillation detectors (plastic or liquid) are characterised by a poor resolution (due to the low Z) and a high efficiency, as they can be used in very large volumes.

Figure 11: Principle of a semi-conductor detector converting Figure 11: Principle of a semi-conductor detector converting an absorbed �-photon into an electric pulse. an absorbed �-photon into an electric pulse. Figure 11: Principle of a semi-conductor detector converting an absorbed �-photon into an electric pulse. A semi-conductor detector can be considered as a solid ionization chamber with two advantages: A semi-conductor detector can be considered as a solid ionization chamber with two advantages: � radio vol30it n4V2.inddis a high 223 density solid compared with the gas ionization chamber 3/04/06 16:42:57 � it is a high density solid compared with the gas ionization chamber � an energy between 3 and 7 eV is enough to produce an electron-hole pair instead A semi-conductor detector can� be consideredan energy asbetween a solid 3ionization and 7 eV chamberis enough with to produce two advantages: an electron-hole pair instead � it is a high density solid compared with the gas ionization chamber � an energy between 3 and 7 eV is enough to produce an electron-hole pair instead A semi-conductor detector can be considered as a solid ionization chamber The energy resolution of a detector is often described by: with two advantages: where FWHM is the full width at half maximum height and E the photon • it is a high density solid compared with the gas ionization energy (resolution ≈ 1%). chamber • an energy between 3 and 7 eV is enough to produce an electron- hole pair instead of 30 eV in an ionization chamber. HPGe detector

The result is a better energy resolution. Other parameters to be considered Ge(Li) detectors must be continuously cooled with liquid nitrogen, for the choice and the design of a semi-conductor detector: or cryogenic pumps, because the small band-gap (0.63 eV) generates a leakage current at room temperature and when the detector is not cooled, • High atomic14 number, Z, to favor the photoelectric effect, the diffusion of lithium in the material destroys the detection property of of 30 eV in an ionization• chamber. High band gap to reduce the electronic noise, the crystal.

The result is a better energy resolution.• The Other product parameters of tothe be consideredmobility for of the the choice charge and the carriers and their lifetime design of a semi-conductor detector: must be high (μ•τ). This characteristic can only be obtained with Since the development of hyper pure germanium (with less than � High atomic number, Z, to favorhigh the purityphotoelectric materials, effect, 0.1 ppb of impurities), this type of detector, replaces the Ge(Li) and has � High band gap to reduce• the electronicThe depleted noise, zone must be optimized to the investigated energy of been increasingly used for in-vivo radioactive burden assessments. The � The product224 of the mobility of the charge carriers and their lifetime must be high (�·�). This characteristic can only be obtainedthe collectedwith high purity photons, materials, Li is not necessary to compensate the impurities in the material and the � The depleted zone must •be optimizedThe to the ionizing investigated energy efficiency of the collected must photons, be high. The detector has to be cooled only during working conditions. Its excellent B � � G � The ionizing efficiency must ionizingbe high. The efficiency ionizing efficiency is defined is defined by: by: ion resolution (1% at 122 keV and 1.5% at 1.33 MeV), must be compared Ee�h

(BG = width of the forbidden gap,(BG E e-h = = widthmean energy of for the the forbidden production of a gap, electron-hole Ee-h = mean energy for the to two major disadvantages with respect to the NaI(Tl) scintillator: the pair). production of a electron-hole pair). efficiency decreases rapidly with energy and the necessity for cooling

Four different processes can generate charge carriers: thermal generation, charge injection (the (with liquid nitrogen, cryogenic pumps or reverse Stirling cycle pumps). principle of the transistor),Four photo-generation, different aprocessesnd a high electric can field generate (avalanche charge process). carriers: The thermal generation, photo-generation is optimized in a semi-conductor detector. charge injection (the principle of the transistor), photo-generation, and a An isolated semi-conductorhigh (p or electricn type) cannot field be used(avalanche to make a radiation process). detector The because photo-generation the is optimized Silicon detector signal will not be visible above the current produced by the majority carriers. This is the reason why a diode is used as the two majorityin a semi-conductor carriers compensate for detector. each other in a "depleted zone". A hyper- pure crystal can be used as radiation detector. Many semi-conductor diodes can be used for the detection and the spectrometry of ionizing radiation. The energy resolution of a detector is often Silicon detectors have good efficiency in the low energy region. described by: An isolated semi-conductor (p or n type) cannot be used to make a radiation Si(Li) diodes 30 mm thick can be used if they are cooled with liquid FWHM detector becauseR � the signal will not be visible above the current produced nitrogen or with a Peltier cell. A silicon diode is preferable to Germanium E where FWHM is the full widthby atthe half majority maximum height carriers. and E theThis photon is energythe reason (resolution why � 1%). a diode is used as the two because of a less prominent escape peak if it is not doped with lithium. majority carriers compensate for each other in a “depleted zone”. A hyper- Technically, the mono-crystal silicon has several advantages: HPGe detectorpure crystal can be used as radiation detector. Many semi-conductor diodes

Ge(Li) detectors mustcan be be continuously used for cool theed withdetection liquid nitrogen, and theor cryogenic spectrometry pumps, of ionizing radiation. because the small band-gap (0.63 eV) generates a leakage current at room temperature and when the detector is not cooled, the diffusion of lithium in the material destroys the detection property of the crystal.

Since the development of hyper pure germanium (with less than 0.1 ppb of impurities), this type of detector, replaces the Ge(Li) and has been increasingly used for in-vivo radioactive burden assessments. The Li is not necessary to compensate the impurities in the material and the detector has to be cooled onlyradio duringvol30 n4V2.indd working 224 conditions. Its excellent resolution (1% at 122 keV and 1.5% 3/04/06 16:42:59 at 1.33 MeV), must be compared to two major disadvantages with respect to the NaI(Tl) scintillator: the efficiency decreases rapidly with energy and the necessity for cooling (with liquid nitrogen, cryogenic pumps or reverse Stirling cycle pumps).

Silicon detector

Silicon detectors have good efficiency in the low energy region. Si(Li) diodes 30 mm thick can be used if they are cooled with liquid nitrogen or with a Peltier cell. A silicon diode is preferable 14 of 30 eV in an ionization chamber.

The result is a better energy resolution. Other parameters to be considered for the choice and the design of a semi-conductor detector:

� High atomic number, Z, to favor the photoelectric effect, � High band gap to reduce the electronic noise, � The product of the mobility of the charge carriers and their lifetime must be high (�·�). This characteristic can only be obtained with high purity materials, � The depleted zone must be optimized to the investigated energy of the collected photons,

BG � The ionizing efficiency must be high. The ionizing efficiency is defined by: �ion � Ee�h

(BG = width of the forbidden gap, Ee-h = mean energy for the production of a electron-hole pair).

Four different processes can generate charge carriers: thermal generation, charge injection (the principle of the transistor), photo-generation, and a high electric field (avalanche process). The photo-generation is optimized in a semi-conductor detector.

An isolated semi-conductor (p or n type) cannot be used to make a radiation detector because the signal will not be visible above the current produced by the majority carriers. This is the reason why a diode is used as the two majority carriers compensate for each other in a "depleted zone". A hyper- pure crystal can be used as radiation detector. Many semi-conductor diodes can be used for the detection and the spectrometry of ionizing radiation. The energy resolution of a detector is often described by: FWHM A semi-conductor detector can be considered as a solid ionization chamber The energy resolution of a detector is often described by: R � E with two advantages: where FWHM is the fullwhere width FWHM at half is maximumthe full width height at half maxandimum E the height photon and E the photon energy (resolution � 1%). • it is a high density solid compared with the gas ionization energy (resolution ≈ 1%). chamber HPGe detector • an energy between 3 and 7 eV is enough to produce an electron- hole pair instead of 30 eV in an ionization chamber. HPGe detector Ge(Li) detectors must be continuously cooled with liquid nitrogen, or cryogenic pumps, because the small band-gap (0.63 eV) generates a leakage current at room temperature and when The result is a better energy resolution. Other parameters to be considered Ge(Li) detectors mustthe detector be continuously is not cooled, cooledthe diffusion with of liquid lithium nitrogen, in the material destroys the detection property of the crystal. for the choice and the design of a semi-conductor detector: or cryogenic pumps, because the small band-gap (0.63 eV) generates a leakage current at room temperature Since the and development when the of detector hyper pure is germaniumnot cooled, (with less than 0.1 ppb of impurities), this • High atomic number, Z, to favor the photoelectric effect, the diffusion of lithium intype the of materialdetector, replaces destroys the theGe(Li) detection and has beenproperty increasingly of used for in-vivo radioactive burden assessments. The Li is not necessary to compensate the impurities in the material and the detector • High band gap to reduce the electronic noise, the crystal. has to be cooled only during working conditions. Its excellent resolution (1% at 122 keV and 1.5% • The product of the mobility of the charge carriers and their lifetime at 1.33 MeV), must be compared to two major disadvantages with respect to the NaI(Tl) scintillator: must be high (μ•τ). This characteristic can only be obtained with Since the developmentthe efficiency of hyper decreases pure rapidlygermanium with energy (with and less the thannecessity for cooling (with liquid nitrogen, high purity materials, 0.1 ppb of impurities), thiscryogenic type of pumps detector, or reverse replaces Stirling the cycle Ge(Li) pumps). and has • The depleted zone must be optimized to the investigated energy of been increasingly used for in-vivo radioactive burden assessments. The the collected photons, Li is not necessary to compensate theSilicon impurities detector in the material and the 225 • The ionizing efficiency must be high. The detector has to be cooled only during working conditions. Its excellent Silicon detectors have good efficiency in the low energy region. Si(Li) diodes 30 mm thick ionizing efficiency is defined by: resolution (1% at 122 keVcan beand used 1.5% if they at are 1.33 cooled MeV), with liquid must nitrogen be compared or with a Peltier cell. A silicon diode is preferable

(BG = width of the forbidden gap, Ee-h = mean energy for the to two major disadvantages with respect to the NaI(Tl) scintillator: the production of a electron-hole pair). efficiency decreases rapidly with energy and the necessity for cooling (with liquid nitrogen, cryogenic pumps or reverse Stirling cycle pumps). Four different processes can generate charge carriers: thermal generation, charge injection (the principle of the transistor), photo-generation, and a high electric field (avalanche process). The photo-generation is optimized Silicon detector in a semi-conductor detector. Silicon detectors have good efficiency in the low energy region. An isolated semi-conductor (p or n type) cannot be used to make a radiation Si(Li) diodes 30 mm thick can be used if they are cooled with liquid detector because the signal will not be visible above the current produced nitrogen or with a Peltier cell. A silicon diode is preferable to Germanium by the majority carriers. This is the reason why a diode is used as the two because of a less prominent escape peak if it is not doped with lithium. majority carriers compensate for each other in a “depleted zone”. A hyper- Technically, the mono-crystal silicon has several advantages: pure crystal can be used as radiation detector. Many semi-conductor diodes can be used for the detection and the spectrometry of ionizing radiation.

radio vol30 n4V2.indd 225 3/04/06 16:43:01 15 to Germanium because of a less prominent escape peak if it is not doped with lithium. Technically, the •mono-crystal It can be silicongrown has with several high advantages: dimensions (20 cm diameter), Unfortunately, impurity problems during manufacturing and abnormal • It is based on a cheap and well mastered technology, leakage currents with variable noise limit the size of this detector to 1 mm � It• canThe be grown pre-amplifier with high dimensions can be (20 integrated cm diameter), on the wafer, eliminating and the applications to optico-electronics. The ternary compound GaAlAs � It is microphonicsbased on a cheap and well mastered technology, presents more stable characteristics, but its use in in vivo counting has � The pre-amplifier can be integrated on the wafer, eliminating microphonics � The• Thelife-time life-time of the chargeof the carrierscharge is carriers high. is high. been limited to the examination of wounds. � The• Thecharacteristics characteristics of silicon of are silicon more arestable more with stabletime. with time. � It• doesIt does not require not require high bias high voltage bias (50V-150 voltage V (50V-150 instead of 800V instead V for the of PMT). 800 V for New detectors and new associations of existing detection media also the PMT). have been used to develop specific in vivo counting devices. They will be discussed later in this paper. 8000

7000 The Calibration of the counting device 6000

5000 -10 V -20 V 4000 Purpose -40 V 3000 -50 V Counts/Channel 2000 The calibration of the counting device is necessary to allow

1000 quantitative assessment of radioactive body burdens. Each calibration is

226 0 specific to the different measurements (Whole body, lungs, wounds, lever, 0 20 40 60 80 100 lymph nodes, head,…). Channel Number (0.75 keV/channel) Calibration with human being: Not ethic, useless and Fig. 12: Effect of the bias voltage on the position, amplitude, and the area of the photoelectric peak in a silicon diode S3590-05 (500µm). impossible

CdZnTe, CdTe, GaAs and GaAlAs detectors CdZnTe, CdTe, GaAs and GaAlAs detectors It is not practical to calibrate detectors with actual body contamination for several reasons. Radionuclides incorporated into the The CdTe The detectorCdTe detector has been studiedhas been for more studied than 20 for years more and isthan commercially 20 years available and for the measurement of plutonium in a wound. However, it is subject to irreversible defects at the body will be quickly metabolized and therefore, impossible to localize in is commercially available for the measurement of plutonium in a wound. contact after several months of biasing. The ternary compound CdZnTe (CZT), which is much more the body so that any calibration acquired under these conditions would stableHowever, than CdTe, it isis now subject available to irreversibleand used currently defects in in-Viv at theo counting. contact after several be unreliable. In addition: the human body is variable in size, shape, months of biasing. The ternary compound CdZnTe (CZT), which is much This binary semi-conductor GaAs, which has a high band gap (1.42 eV), can work at room- composition and attenuation characteristics and these differences will all more stable than CdTe, is now available and used currently in in-Vivo temperature with properties similar to Ge. Unfortunately, impurity problems during manufacturing lead to complications with calibration. It is also unethical to expose persons andcounting. abnormal leakage currents with variable noise limit the size of this detector to 1 mm and the applications to optico-electronics. The ternary compound GaAlAs presents more stable to an unnecessary exposure or contamination. characteristics, but its use in in vivo counting has been limited to the examination of wounds. This binary semi-conductor GaAs, which has a high band gap (1.42 eV), Newcan detectors work andat room-temperature new associations of withexisting properties detection similarmedia also to haveGe. been used to develop specific in vivo counting devices. They will be discussed later in this paper.

radio vol30 n4V2.indd 226 3/04/06 16:43:03 • It can be grown with high dimensions (20 cm diameter), Unfortunately, impurity problems during manufacturing and abnormal • It is based on a cheap and well mastered technology, leakage currents with variable noise limit the size of this detector to 1 mm • The pre-amplifier can be integrated on the wafer, eliminating and the applications to optico-electronics. The ternary compound GaAlAs microphonics presents more stable characteristics, but its use in in vivo counting has • The life-time of the charge carriers is high. been limited to the examination of wounds. • The characteristics of silicon are more stable with time. • It does not require high bias voltage (50V-150 V instead of 800 V for New detectors and new associations of existing detection media also the PMT). have been used to develop specific in vivo counting devices. They will be discussed later in this paper.

The Calibration of the counting device

Purpose

The calibration of the counting device is necessary to allow quantitative assessment of radioactive body burdens. Each calibration is specific to the different measurements (Whole body, lungs, wounds, lever, 227 lymph nodes, head,…).

Calibration with human being: Not ethic, useless and impossible

CdZnTe, CdTe, GaAs and GaAlAs detectors It is not practical to calibrate detectors with actual body contamination for several reasons. Radionuclides incorporated into the The CdTe detector has been studied for more than 20 years and body will be quickly metabolized and therefore, impossible to localize in is commercially available for the measurement of plutonium in a wound. the body so that any calibration acquired under these conditions would However, it is subject to irreversible defects at the contact after several be unreliable. In addition: the human body is variable in size, shape, months of biasing. The ternary compound CdZnTe (CZT), which is much composition and attenuation characteristics and these differences will all more stable than CdTe, is now available and used currently in in-Vivo lead to complications with calibration. It is also unethical to expose persons counting. to an unnecessary exposure or contamination.

This binary semi-conductor GaAs, which has a high band gap (1.42 eV), can work at room-temperature with properties similar to Ge.

radio vol30 n4V2.indd 227 3/04/06 16:43:03 16 The Calibration of the counting device

Purpose

The calibration of the counting device is necessary to allow quantitative assessment of radioactive body burdens. Each calibration is specific to the different measurements (Whole body, lungs, wounds, lever, lymph nodes, head,…).

Calibration with human being: Not ethic, useless and impossible

It is not practical to calibrate detectors with actual body contamination for several reasons. Radionuclides incorporated into the body will be quickly metabolized and therefore, impossible to localize in the body so that any calibration acquired under these conditions would be unreliable. In addition: the Use human of phantoms: body is variable the in best size, solution shape, composition and attenuation characteristics and these differences will all lead to complications with calibration. It is also unethical to expose persons to an unnecessary exposure or contamination. Usually, plastic bottles with an aqueous solution of nuclides comprise Use of the phantoms: system the easy best to solution use. The phantom most often used was

developed Usually, by plastic Bush bottles and afterwith animprovements aqueous solution is of now nuclides called comprise the BOMAB the system easy to use.phantom The phantom (BOttle-Manikin most often used was ABsorption). developed by It Bush consists and after of improvements 10 polyethylene is now called the BOMABbottles (tablephantom 2) (BOttle-Manikin and is shown ABsorption).in Fig. 13a. ItThis cons phantomists of 10 polyethylene simulates bottlesthe body (table 2) and isof shown an adult in Fig. male 13a. ofThis 68.3 phantom kg. simulates the body of an adult male of 68.3 kg. Body parts Cross-section (cm) Height (cm) Volume (l) Head Elliptic 19 x 14 20 4.08 Neck Circle 13 10 0.93 Thorax Elliptic 30 x 20 40 16.6 Pelvis (Abdomen) Elliptic 36 x 20 20 12.9 Thighs Circle 15 40 6.05 x 2 Legs Circle 12 40 3.85 x 2 Arms Circle 10 60 3.92 x 2 228 Total height: 170 cm Total volume: 62.l5 l

TableTable 2: Shape,Shape, sizes sizes and and volume volume of the of BOMAB the BOMAB phantoms phantoms used at the used SCK �atCEN the n Mol. SCK•CEN in Mol. Special types of phantoms have been developed: the Lauwrence Livermore phantom (Fig. 13b) has been created for the measurements of contaminated lungs, lever and mediastal lymph nodes. ThisSpecial phantom types represents of phantoms a Caucasian have been morphol developed:ogy. For the the oriental Lauwrence morphologies, JAERI has conceivedLivermore a special phantom abdo-torso (Fig. phantom 13b) has for been most ofcreated the measurements for the measurements encountered in occupational contaminations (Fig. 13c). Specialof contaminated phantoms are lungs, used to lever measure and localised mediastal contaminations: lymph nodes. the Thisthyroid phantom is simulated by two vialsrepresents in a polymethylmetacrylate a Caucasian morphology. cylinder simulating For the theoriental throat morphologies,(Fig.14, bottom-right). In Fig. 14 (top-center)JAERI has is alsoconceived shown a kneea special phantom abdo-torso developed phantom(H. Spitz – forCincinnati) most of for the the measurement of 241 152 measurementsAm and Eu in encountered the patella. in occupational contaminations (Fig. 13c). Special phantoms are used to measure localised contaminations: the thyroid is simulated by two vials in a polymethylmetacrylate cylinder simulating the throat (Fig.14, bottom-right). In Fig. 14 (top-center) is also shown a knee phantom developed (H. Spitz – Cincinnati) for the measurement of 241Am and 152Eu in the patella.

radio vol30 n4V2.indd 228 3/04/06 16:43:05 17

Use of phantoms: the best solution

Usually, plastic bottles with an aqueous solution of nuclides comprise the system easy to use. The phantom most often used was developed by Bush and after improvements is now called the BOMAB phantom (BOttle-Manikin ABsorption). It consists of 10 polyethylene bottles (table 2) and is shown in Fig. 13a. This phantom simulates the body of an adult male of 68.3 kg.

a b c BOMAB phantom Livermore torso phantom JAERI torso phantom

Figure 13: Three types of phantoms

229

Table 2: Shape, sizes and volume of the BOMAB phantoms used at the SCK•CEN in Mol.

Special types of phantoms have been developed: the Lauwrence Livermore phantom (Fig. 13b) has been created for the measurements of contaminated lungs, lever and mediastal lymph nodes. This phantom represents a Caucasian morphology. For the oriental morphologies, JAERI has conceived a special abdo-torso phantom for most of the measurements encountered in occupational contaminations (Fig. 13c). Special phantoms are used to measure localised contaminations: the thyroid is simulated by two vials in a polymethylmetacrylate cylinder simulating the throat (Fig.14, bottom-right). In Fig. 14 (top-center) is also shown a Figure 14: Other types of phantoms knee phantom developed (H. Spitz – Cincinnati) for the measurement of From left to right: 241 152 Row 1: Torso with true thoracic cage, Knee with plastic bones, Shmier phantom with soda Am and Eu in the patella. plastic bottles (Greak Atomic Energy Commission) Row 2: PMM torso (Canberra), Torso from BOMAB for Uranium, Thryroïd (PMM).

radio vol30 n4V2.indd 229 3/04/06 16:43:09 Mathematical or numerical calibration phantoms

It is possible to simulate a body (entirely or partially) containing radioactive distributions by using computer programs. The attenuation of γ-rays by tissue can be calculated to provide, in many cases, accurate results for a body burden non obtainable by experimental18 procedures . Deterministic programme (ATT3D) or Monte Carlo programmes such as MCNP can be used for this purpose. Mathematical or numerical calibration phantoms

It is possible to simulate a body (entirely or partially) containing radioactive distributions by using Ancomputer example programs. of TheMCNP attenuation calculation, of �-rays by given tissue can below be calculated shows to aprovide, plastic in phantom many cases, accurate results for a body burden non obtainable by experimental procedures . inDeterministic tilted chair programme position (ATT3D) measured or Monte withCarlo programmesa thin NaI(Tl) such as MCNPdetector can be(Fig. used 15).for This figurethis purpose. presents the counting efficiencies for three different energies as a function

of the detector An example position of MCNP calculation,when this given is movedbelow shows along a plastic the phantomsymmetrical in tilted axischair between theposition two measuredextreme with indicated a thin NaI(Tl) positions. detector (Fig. The 15). last This curve figure (efficiency presents the countingfor 60 keV) is efficiencies for three different energies as a function of the detector position when this is moved multipliedalong the symmetrical by 20 toaxis allow between an the easytwo extreme comparison). indicated positions. The last curve (efficiency for 60 keV) is multiplied by 20 to allow an easy comparison).

230

The major advantages of the mathematical phantoms are:

• Easy to model simple phantoms 0.0045 • Possibility to improve accuracy of measurement ) 0.004 (if contamination position is known: obesity, infants, hot 0.0035 0.003 spots,…..) 661.6 keV 0.0025 • Optimization of geometry 1460. keV 0.002 60 keV (x 20) • Possibility to manage detection limits 0.0015 • Prospective study 0.001 Counting Efficiency (C/(s.Bq Efficiency Counting 0.0005 • Improve the accuracy of the assessment of dose 0 -40 -20 0 20 40 60 80 Detector position (cm)

Fig. 15: Effect of longitudinal displacement of detector on efficiency for tilted chair position.

radio vol30 n4V2.indd 230 3/04/06 16:43:10 19

Fig. 16 presents the effect of the azimuthal position of the detector when this is moved apart from the torso. Fig. 16 presents the effect of the azimuthal position of the detector when this is moved apart from the torso.

Effect of azimuthal position

0.00500

0.00400

0.00300

0.00200 Efficiency 0.00100

0.00000 0 10 20 30 40 50 231 Relative Position (cm)

Fig. 16: Simulation of a body in supine position. The detector is placed in front of the torso. The relative distance, d, is counted from the table supporting the body. The major advantages of the mathematical phantoms are: The major advantages of the mathematical phantoms are: • Easy to model simple phantoms • Easy to model simple phantoms • Possibility• Possibility to improve to improve accuracy ofaccuracy measurement of measurement (if contamination (if contamination position is known: position is obesity, known: infants,obesity, infants, hot hot spots,…..) • Optimizationspots,…..) of geometry • Possibility• Optimization to manage ofdetection geometry limits • Prospective study • Improve• Possibility the accuracy to manageof the assessment detection of doselimits • Prospective study • Improve the accuracy of the assessment of dose

radio vol30 n4V2.indd 231 3/04/06 16:43:12

The first step is the acquisition of a energy spectrum of the Ê-rays collected For the identification of the radionuclides and their quantification, the by the detector. The analysis of this spectrum requires the identification of analysis of a spectrum can be undertaken by two methods: the radionuclides and their burden in the body or in the organs. • the photopeak location and peak area method, Generally, a spectrum collected into 200 channels is sufficiently detailed • the least square method using standard spectra to fit a wide portion of for a NaI(Tl) detector whereas a spectrum of 2000, 4000 channels is the spectrum. preferably used with a semiconductor detector. An example is these spectra is shown in Fig. 18. Peak area method

A photopeak is first located by scanning (visually or automatically) the spectrum, the centroïd of each peak is next defined, and converted to an energy using the channel-energy for isotope identification. Sometimes and specially when different photopeaks are near to each other, special deconvolution techniques are necessary.22

special Oncedeconvolution the radionuclides techniques are are necessary. identified, measuring the area of the photopeak by an absolute or a relative method provides the information necessary in 234 Once theobtaining radionuclides the activityare identified, estimate. measuring The peaks,the area whichof the photopeakappear in by the an spectrum,absolute or a relative method provides the information necessary in obtaining the activity estimate. The peaks, which appearcan be in fittedthe spectrum, with Gaussian can be fitted functions with Gaussian after functions determination after determination of a base of linea base line (Fig.(Fig. 19). 19).

Fig. 18: General view of a WBC spectrum collected with a 20 cm diameter × 10 cm thick NaI(Tl) detector crystal. Fig.Fig. 19: 19: Three Three different different techniques techniques to determine to determine the net area the S of net a photopeak area S of a in a �-ray spectrum (straight line,photopeak quadratic curve, Galton curve). Determinationin ofa activityγ-ray spectrum requires an (straight efficiency line, curve quadratic for each detector curve, configuration Galton curve). and for each counting geometry (tilting chair, bed, organ...). A typical expression for the efficiency curve as a function of energy E for a scintillation detector is given by:

=R(E) � E� -(1 E�E )

radio vol30 n4.indd 237 S 23/03/06 9:56:32 =Act t.p.R(E)

These functions convert peak area to a radioactive body burden using the following parameters:

E Photon energy (keV or MeV,…), R(E) Efficiency of the counting device and corresponding to a specific geometry, Act Required activity in the body (Bq) t Counting time (sec), S Photopeak area (counts) P Probability (or branching ratio) of the � transition for the investigated nuclide. �, �, � Energy-Efficiency parameters determined experimentally.

A radiation detector is generally characterised by its relative efficiency or its intrinsic efficiency or 22 special deconvolution techniques are necessary.

Once the radionuclides are identified, measuring the area of the photopeak by an absolute or a relative method provides the information necessary in obtaining the activity estimate. The peaks, which appear in the spectrum, can be fitted with Gaussian functions after determination of a base line (Fig. 19).

Fig. 19: Three different techniques to determine the net area S of a photopeak Determinationin a �-ray of spectrumactivity (straightrequires line, an quadratic efficiency curve, curve Galton for curve). each detector configuration and for each counting geometry (tilting chair, bed, organ...). Determination of activity requires an efficiency curve for each detector configuration and for each countingA typical geometry expression (tilting chair, for bed, the organ...).efficiency A typical curve expressionas a function for the of efficiency energy E curve for as a functiona scintillation of energy E fordetector a scintillation is given detector by: is given by:

R(E)=� E� (1- E�E )

S Act = t.p.R(E)

These functions convert peak area to a radioactive body burden using the following parameters: These functions convert peak area to a radioactive body burden using the followingE parameters: Photon energy (keV or MeV,…), R(E) Efficiency of the counting device and corresponding to a specific geometry, Act Required activity in the body (Bq) t E CountingPhoton time (sec), energy (keV or MeV,…), S R(E) Photopeak Efficiency area (counts) of the counting device and P Probability (or branching ratio) of the � transition for the investigated nuclide. corresponding to a specific geometry, 235 �, �, � Act Energy-Efficiency Required parameters activity indetermined the body experimentally. (Bq) t Counting time (sec), S Photopeak area (counts) A radiation detectorP is generally Probabilitycharacterised (orby its branching relative efficiency ratio) of or theits intrinsic γ transition efficiency or for the investigated nuclide. α, β, γ Energy-Efficiency parameters determined experimentally.

A radiation detector is generally characterised by its relative efficiency or its intrinsic efficiency or its counting efficiency.

The computerised analysis of a NaI(Tl) spectrum based on the peak area method is shown in Fig. 20. The figure presents the spectrum of a BOMAB phantom filled with an aqueous solution of KCl with a concentration such that the total activity of 40K in this phantom is 4600 Bq. The energy calibration of this spectrum is 10 keV/channel. The straight 23

its counting efficiency.

The computerised analysis of a NaI(Tl) spectrum based on the peak area method is shown in Fig. 20. The figure presents the spectrum of a BOMAB phantom filled with an aqueous solution of KCl with a concentration such that the total activity of 40K in this phantom is 4600 Bq. The energy calibrationline fitting of thisthe spectrumbackground is 10 keV/channel.is derived from The straightsix points line fittingon either the background side of the is derived fromphotopeak. six points The on either second side graph,of the photopeak. shown above The second the photopeak, graph, shown is above the residual the photopeak, is theof residualthe fitting of the showing fitting showing that a Gaussian that a Gau curvessian curve is a veryis a very good good approximation approximation for the description of a photopeak obtained with a NaI(Tl) scintillator. for the description of a photopeak obtained with a NaI(Tl) scintillator.

236

Fig. 20: Analysis of a �-spectrum by the peak area determination.

Fig. 21 presents a spectrum of 131I in the thyroid where the continuum under the photopeak is best simulated by a quadratic curve fitted with several points on each side of the photopeak. Fig. 21 presents a spectrum of 131I in the thyroid where the continuum under the photopeak is best simulated by a quadratic curve fitted with several points on each side of the photopeak. 24

237

Fig. 21: Continuum under a photopeak calculated with a quadratic curve. 131 (SpectrumFig. 21:of ContinuumI in the thyroid under with aa photopeak5×5 cm NaI(Tl) calculated with a dispersion with a quadraticof 5 keV/channel) curve. (Spectrum of 131I in the thyroid with a 5×5 cm NaI(Tl) with a dispersion of 5 keV/channel) Least square fitting on the whole spectrum

When the resolution is not sufficient, peak deconvolution is not possible when several photo-peaks appear together on the spectrum and overlap each other. This is the case when spectra of multiple radionuclides are collected with NaI(Tl) detectors or with the more recently used CdZnTe diode which is characterized by an unequal collection of electrical charges.

The peak area method is also characterized by a detection limit sometimes too high. 25

It is possible to reduce this LD and analyze complex γ-ray spectra by Least squareusing fitting the onleast the squarewhole spectrum fitting applied on the whole spectrum. The method assumes that the value in each channel of the composite spectrum equals 238 Whenthe thesum resolution of the values is not sufficient,of the same peak channel deconvolution in the differentis not possible isolated when spectra. several photo-peaksThe appear efficacy together of onthis the method spectrum can and overlbe adverselyap each other. affected This is theif the case shape when spectraof the of multiple radionuclides are collected with NaI(Tl) detectors or with the more recently used CdZnTe diodebackground which is characterizedcontinuum bychanges an unequal as cancollection sometimes of electrical happen charges. with muscular persons. These adverse effects generally occur when the activity being The peak areameasured method isis alsolow. characteri In the standardzed by a detection methods limit technique, sometimes the too entirehigh. spectrum, or a wide portion, is examined. The net count rate in each channel may It is possible to reduce this LD and analyze complex �-ray spectra by using the least square fitting applied onbe the representedwhole spectrum. by The the method sum of assumes the weighted that the value contribution in each channel of ofeach the compositestandard spectrum equalsspectrum, the sum which of the were values obtained of the same using channel phantoms in the different measured isolated under spectra. the same The efficacy of this method can be adversely affected if the shape of the background continuum changes as can sometimesgeometrical happen conditions: with muscular persons. These adverse effects generally occur when the activity being measured is low. In the standard methods technique, the entire spectrum, or a wide portion, is examined. The net count rate in each channel may be represented by the sum of the weighted contribution of each standard spectrum, which were obtained using phantoms measured under the same geometrical conditions:

m N(i)= Bkg(i)+ � w(i).S(i, j).a(j)+ Ei for i = 1,n j=1

where: N(i) is the number of counts in channel i (measured), Bkg(i) the number of counts in the background in channel i, S(i,j) the number of counts in channel i from standard j, a(j) the activity of standard j in the measured spectrum, w(i) the statistical weighting factor for the content of channel i, Ei the statistical error in channel i during the counting, m number of radionuclides in the mixture. n total number of channels.

The calculation of the activity of each radionuclide a(j) on the basis of the highest probability is obtained by minimising the value of the reduced �2:

n 2 � 2 = E i � � 2 i=1 (n - m)� i

where v=(n-m) Number of degrees of freedom, 2 � i Variance on Ei.

This method is of particular use for the detection of radionuclides in spectra where the photopeaks are not clearly visible.

Fig. 22 shows the spectrum simulating a person contaminated by a mixture of 137Cs, 140Ba and 25

Least square fitting on the whole spectrum 25

Least square fitting on the whole spectrum When the resolution is not sufficient, peak deconvolution is not possible when several photo-peaks appear together on the spectrum and overlap each other. This is the case when spectra of multiple radionuclides are collected with NaI(Tl) detectors or with the more recently used When the resolution is not sufficient,CdZnTe peak deconvolution diode which isis characterized not possible bywhen an unequalseveral collection of electrical charges. photo-peaks appear together on the spectrum and overlap each other. This is the case when spectra of multiple radionuclides are collected withThe NaI(Tl peak) detectorsarea method or withis also the characteri more recentlyzed by a used detection limit sometimes too high. CdZnTe diode which is characterized by an unequal collection of electrical charges. It is possible to reduce this LD and analyze complex �-ray spectra by using the least square fitting The peak area method is also characterized byapplied a detection on the limit whole sometimes spectrum. too The high. method assumes that the value in each channel of the composite spectrum equals the sum of the values of the same channel in the different isolated spectra. The efficacy of this method can be adversely affected if the shape of the background continuum changes It is possible to reduce this LD and analyze complex �-ray spectra by using the least square fitting applied on the whole spectrum. The method assumesas can sometimesthat the value happen in each with channel muscular of the persons. composite These adverse effects generally occur when the spectrum equals the sum of the values of the activitysame channel being measuredin the different is low. isolated In the standard spectra. methods The technique, the entire spectrum, or a wide efficacy of this method can be adversely affectedportion, if the shapeis examined. of the ba Theckground net count continuum rate in changeseach channel may be represented by the sum of the as can sometimes happen with muscular persons.weighted These contribution adverse effects of each generally standard occur spectr whenum, the which were obtained using phantoms measured activity being measured is low. In the standardundermethods the same technique, geometrical the entire conditions: spectrum, or a wide portion, is examined. The net count rate in each channel may be represented by the sum of the m weighted contribution of each standard spectrum, which were obtained using phantoms measured N(i)= Bkg(i)+ � w(i).S(i, j).a(j)+ Ei for i = 1,n under the same geometrical conditions: j=1

m N(i)= Bkg(i)+ w(i).S(i, j).a(j)+ for i = 1,n where: N(i) is the number of counts� inwhere: channel i (measured),Ei N(i) is the number of counts in channel i (measured), j=1 Bkg(i) the number of counts in the background inBkg(i) channel i, the number of counts in the background in channel i, S(i,j) the number of counts in channel i from standardS(i,j) j, the number of counts in channel i from standard j, a(j) the activity of standard j in the measured spectrum, where: a(j) the activity N(i) of standard is the j numberin the measuredof counts in spectrum, channel i (measured), Bkg(i) the number of counts in the backgroundw(i) in channel the statistical i, weighting factor for the content of channel i, w(i) the statisticalS(i,j) weighting the number factor of for counts the incontent channelE ofi i fromchannel standard i, the j,statistical error in channel i during the counting, E the statisticala(j) error in the channel activity of i duringstandard the j in counting,them measured spectrum, number of radionuclides in the mixture. i n total number of channels. m numberw(i) of radionuclides the statistical in the weightingmixture. factor for the content of channel i, E the statistical error in channel i during the counting, n total numberi of channels. The calculation of the activity of each radionuclide a(j) on the basis of the highest probability is m number of radionuclides in the mixture. 2 n total numberobtained of channels. by minimising the value of the reduced � :

The calculation of the activity of each radionuclide a(j) on the basis of the n 2 The calculation of the activity of each radionuclide a(j) on the basis of the highest probability2 is � = E i highest probability is obtained by minimising2 the value of the reduced �: � 2 obtained by minimising the value of the reduced � : i=1 (n - m)� i

n 2 � 2 = E i � �where 2 v=(n-m) Number of degrees of freedom, i=1 (n - m)� i 2 � i Variance on Ei. where v=(n-m) NumberThis of degrees method of is freedom,of particular use for the detection of radionuclides in spectra where the photopeaks 2 are not clearly visible. � i Variance on Ei. 239 137 140 This method is of particular use for the detectionFig. of 22 radionuclides shows the spectrum in spectra simulating where the a photopeaks person contaminated by a mixture of Cs, Ba and areThis not method clearly visible. is of particular use for the detection of radionuclides in spectra where the photopeaks are not clearly visible. Fig. 22 shows the spectrum simulating a person contaminated by a mixture of 137Cs, 140Ba and Fig. 22 shows the spectrum simulating a person contaminated by a mixture of 137Cs, 140Ba and 60Co. The decision as to which radionuclides are present is made on a statistical basis with the aid of the residual spectrum that shows the discrepancies in each channel between the measured spectrum and the calculated one. 26

60Co. The decision as to which radionuclides are present is made on a statistical basis with the aid of the residual spectrum that shows the discrepancies in each channel between the measured spectrum and the calculated one.

Fig. 22: Example of results of an analysis using the standard method 137 Geometry: Tilted chair. Counting time: 2000 sec. LD for Cs: 4 Bq. 240 Energy range: 100 keV - 2. MeV. The detection limit for the 20 cm x 10 cm detector is reduced to 4 Bq in The detection limit for the 20 cm x 10 cm detector is reduced to 4 Bq in 137Cs, for a counting time 137 of 2000 seconds.Cs, Thisfor procedurea counting can time provide of very2000 short seconds. count time This resulting procedure in sensitivities can provide low enough to meetvery the short regulations count for time most resulting of the radionuclides in sensitivities found near low nuclear enough reactor to plants meet and the accelerators.regulations for most of the radionuclides found near nuclear reactor plants The advantageand of accelerators. the least square method is a better detection limit. The least square fitting is often the only method able to analyze a spectrum, using a NaI(Tl) detector, when more than three radionuclides (other than 40K) are present in the body. Whole body counting can be used for some pure �-emittersThe (i.e. advantage 90Sr or 32P) of by the measuring least square the Bremmstrahlung method is a ra betterdiation, detection but the identity limit. of Thethe radionuclidesleast must square be known fitting in this is case. often For the all these only reasons, method the able least stoquare analyze fitting ona spectrum, the whole spectrum isusing the only a issue NaI(Tl) to allow detector, a NaI(Tl) scin whentillator more to perform than routine three measurements radionuclides of WBC. (other The peak area fitting dose is not able to calculate the spectrum with pure �-emitters. than 40K) are present in the body. Whole body counting can be used for In the spacesome research pure field, β-emitters the least square (i.e. 90 fittiSrng or is 32 usedP) by for measuringNaI(Tl) detectors the Bremmstrahlungeach time that a large numberradiation, of radionuclides but the or identity nuclear reactionsof the radionuclides are expected (e.g. must in thebe NEAR-known Shoemaker in this case. spacecraft on the surface of 433 Eros meteorite and in the experiments token away with the Lunar ProspectorFor all spaceship). these reasons, the least square fitting on the whole spectrum is the only issue to allow a NaI(Tl) scintillator to perform routine measurements of WBC. The two most used detectors used in WBC are now the NaI(Tl) and the HPGe detectors. They The peak area fitting dose is not able to calculate the spectrum with pure β-emitters. In the space research field, the least square fitting is used for NaI(Tl) detectors each time that a large number of radionuclides or nuclear reactions are expected (e.g. in the NEAR- Shoemaker spacecraft on the surface of 433 Eros meteorite and in the experiments taken away with the Lunar Prospector spaceship).

The two most used detectors used in WBC are now the NaI(Tl) and the HPGe detectors. They are both characterized by their own advantages and problems.

The HPGe has an excellent energy resolution but requires a cooling to work.

The NaI(Tl) has a low energy resolution but its advantages can be summarized as follows:

1. High efficiency low counting time 241 2. Lower detection limits if the LSF method is used for the analysis 3. Possibility to measure pure beta-emitters 4. Usage of all types of interactions 5. No limitation in the number of photopeak when least square fit is adopted. 6. When distribution is different Background, efficiency and detection limits

Background

Effect of material inside the shielded room

Background refers to the signals measured by the detection system whose source is radiation not emitted by a measured subject (e.g. cosmic radiation, terrestrial radiation, radon). Background may also refer to radiation from the individual being counted, but arising from sources other than the radionuclide(s) of interest for the measurement. For example, 40K photons emitted from the equipment and surroundings are considered as a background for the measurement. A background spectrum is obtained either when the measurement sample is not present in the counting room or when an uncontaminated phantom (without 40K) is measured.

242 In a shielded room, the human body increases the background by a factor ranging between 2 and 4.2 in the low energy range (0-200 keV), a factor both energy and detector dependent. The continuum is due to the body’s scattering of the remaining radiation present in the room and from the radiation from 40K and other natural radionuclides present in the body. Layers of high and low Z material in the walls displace the backscattered photons towards the low energies.

Effect of the detector volume on the background

The detector’s volume affects the amplitude of the continuum’s component of the background. For example, two coaxial HPGe crystals with a volume ratio of 1.31 present a continuum ratio of 1.31 +/- 0.03. For this reason, one way to reduce the detection limit of a counting device is to reduce the volume of the detector. 28

Background, efficiency and detection limits

Background

Effect of material inside the shielded room

Background refers to the signals measured by the detection system whose source is radiation not emitted by a measured subject (e.g. cosmic radiation, terrestrial radiation, radon). Background may also refer to radiation from the individual being counted, but arising from sources other than the radionuclide(s) of interest for the measurement. For example, 40K photons emitted from the equipment and surroundings are considered as a background for the measurement. A background spectrum is obtained either when the measurement sample is not present in the counting room or when an uncontaminated phantom (without 40K) is measured.

In a shielded room, the human body increases the background by a factor ranging between 2 and 4.2 in the low energy range (0-200 keV), a factor both energy and detector dependent. The continuum is due to the body's scattering of the remaining radiation present in the room and from the radiation from 40K and other natural radionuclides present in the body. Layers of high and low Z material in the walls displace the backscattered photons towards the low energies.

Effect of the detector volume on the background

The detector's volume affects the amplitude of the continuum's component of the background. For example, two coaxial HPGe crystals with a volume ratio of 1.31 present a continuum ratio of 1.31Counting +/- 0.03. efficiency For this reason, one way to reduce the detection limit of a counting device is to reduce the volume of the detector. In a first consideration, the counting time can be reduced if the Counting efficiencyefficiency is increased by increasing the volume or the number of detectors. But a detector not correctly placed may contribute more to a background In a first consideration, the counting time can be reduced if the efficiency is increased by increasing the volumeenhance or the numb thaner to of andetectors. improvement But a detector of thenot correctlysignal originating placed may contribute from the body. more to a backgroundThe enhance thickness than toof an a improveme detector alsont of thehas signal to be originat considereding from in the a body.similar The manner. thickness of a detector also has to be considered in a similar manner. The thickness required to The thickness required to absorb 90% (L0.1) of an incident photon is given absorb 90% (L0.1) of an incident photon is given by: by: I � exp(�� L � L0.1 ) I 0

For example, the L0.1For for example, germanium the at 60 L keV for is 0.22 germanium cm. Therefore at 60 a, 2cm-thick keV is 0.22 detector cm. used Therefore for a, the measurement of 241Am in the lungs is 100.1 times too thick. If the thickness were to be reduced to 241 0.2 cm, the continuum2cm-thick would bedetector reduced used by a forfactor the of measurement 10 without significantly of Am changingin the lungs the is 10 counting efficiency.times The too detection thick. limitIf the L thicknessC would be were reduced to be by reduced a factor to of 0.2 �3 cm, (i.e., the10 continuum). Comments praisingwould the advantages be reduced of a detector by a factor with a of high 10 relative without efficiency significantly are, therefore, changing the incorrect when the detection limits are considered. 243 counting efficiency. The detection limit LC would be reduced by a factor of ≈3 (i.e.,√10). Comments praising the advantages of a detector with a high relative efficiency are, therefore, incorrect when the detection limits are considered.

Table 3 gives the L0.1 for different materials at 60 keV.

Detector Density kg.m-3 L (m) 0.1 Silicon 2330 0.32 CZT 6200 5.7 10-4 HPGe 5320 2.14 10-3

Table 3: Thickness, L0.1, of different materials required at 60 keV .

29 2929

Table 3 gives the L0.1 for different materials at 60 keV. TableTable 3 3 gives gives the the L 0.1L0.1 for for different different materials materials at at60 60 keV. keV.

-3 Detector Density kg.m L0.1(m) Detector Density kg.m-3 -3 L (m) SiliconDetector Density2330 kg.m L0.320.10.1(m) SiliconSilicon 23302330 0.320.32 -4 CZT 6200 5.7 10 -4 CZTCZT 62006200 5.75.7 10 10-4-3 HPGe 5320 2.14 10 -3 HPGeHPGe 53205320 2.142.14 10 10-3

Table 3: Thickness, L0.1, of different materials required at 60 keV . Table 3: Thickness, L of different materials required at 60 keV . Table 3: Thickness, L0.1,0.1,of different materials required at 60 keV . Detection limits Detection limits DeDetectiontection limits limits The detection limits generally used in WBC (with a 95 % confidence The detection limits generally used in WBC (with a 95 % confidence level) are defined as: The detectionlevel) arelimits defined generally as: used in WBC (with a 95 % confidence level) are defined as: The detection limits generally2.33 B used in WBC (with a 95 % confidence level) are defined as: L � for the a posteriori critical level (L ) C 2.233.33 B B for the a posteriori criticalC level (LC) L �� �t for the a posteriori critical level (LC) LC C� count for the a posteriori critical level (LC) and � � �tcount and tcount and and 2.71� 4.65 B for the a priori detection limit (LD). � LD 2.271.71� 4�.465.65B B for the a priori detection limit (LD). L � � �t for the a priori detection limit (LD). LD D� count for the a priori detection limit (LD). � � �tcount B is the numbertcount of counts in a given energy region of the background B is the numberspectrum, of counts in η a thegiven counting energy region efficiency of the background of the detector spectrum, (counts.s � the counting-1.Bq-1), and B Bis isthe the number number of of counts counts in in a givena given-1 energy-1 energy region region of of the the background background spectrum, spectrum, � �the the counting counting efficiency of the detector (counts.s .Bq-1 ),-1 and tcount the counting time. The detection limits of an in efficiency of thet detector the counting (counts.s-1 time..Bq-1 ), Theand t countdetection the counting limits time. of Thean in detection vivo counting limits of an system in vivoefficiency counting of the system detectorcount are (counts.s function of.Bq both), and the tefficiencycount the counting and the time. local The background. detection limits The optimalof an in thicknessvivovivo counting counting can besystem are systemeasily function are calculated are function function of (if bothof weof both both considerthe the efficiencythe efficiency efficiency a parallel andand fluxand thethe ofthe local photons).local local background. background. We can optimizeThe The Theoptimal optimal theoptimal thicknessthickness can can be be easily easily calculated calculated (if (if we we consider consider a parallela parallel flux flux of of photons). photons). We We can can optimize optimize the the LC by writing: thickness can be easily calculated (if we consider a parallel flux of photons). LCL Cby by writing: writing: We can optimize the LC by writing: 2.33� k'� th � LC 2.233.33� k�'�k'�thth L LC� � S � (1� exp(�1.07 �th) C S� � (�1� exp(� �1.07� �th) 244 S (1 exp( 1.07 th) where S is the cross section of the detector and th the required thickness. The results for different materials,wherewhereS Sis given isthe the cross whereincross Fig. section section 23S isallow of theof the theto cross detector chose detector section th ande andoptimal th th ofthe the therequiredthickness required detector thickness. in thickness. term and of thThe detection The the results results required limits. for for different different thickness. 30 materials,materials, given given Thein in Fig. Fig. results 23 23 allow allow for to to differentchose chose th the optimale materials,optimal thickness thickness given in in term in term Fig. of of detection detection 23 allow limits. limits. to chose the optimal thickness in term of detection limits.

20

2 15 1

10 LC (-) LC 5 3 5 6

4 0 0.01 0.1 1 10 100 Detector thickness (mm)

Fig. 23: Effect of thickness on the critical level LC for different detectors.

1: HPGe at 60 keV - 2: Silicon at 60 keV - 3: CsI(Tl) scintillator at 60 keV – 4: CsI(Tl) at 20 keV - 5: NaI(Tl) scintillator at 60 keV - 6: NaI(Tl) at 20 keV.

If an array of small detectors is used, each with an independent acquisition device, instead of a large detector, the a posteriori analysis of the different spectra allows a selection, eliminating the detectors not contributing positively to the signal.

Is it necessary to reduced the background level indefinitely in case of in vivo counting?

If we examine different background spectra obtained in different shielded conditions (Fig. 24), which have been collected in the following conditions:

1. On table in the laboratory with no shielding,

2. same as the previous one but two days later,

3. same as the previous with addition of a brass collar (3 mm-thick),

4. in the well HADES in Mol at a depth of 225 m (without shielding),

5. in room 5 of the WBC laboratory of the SCK�CEN,

6. in the UDO laboratory in the ASSE mine (-925 m), If an array of small detectors is used, each with an independent acquisition device, instead of a large detector, the a posteriori analysis of the different spectra allows a selection, eliminating the detectors not contributing positively to the signal.

Is it necessary to reduced the background level indefinitely in case of in vivo counting?

If we examine different background spectra obtained in different shielded conditions (Fig. 24), which have been collected in the following conditions:

1. On table in the laboratory with no shielding, 2. same as the previous one but two days later, 3. same as the previous with addition of a brass collar (3 mm-thick), 4. in the well HADES in Mol at a depth of 225 m (without shielding), 31 5. in room 5 of the WBC laboratory of the SCK•CEN, 245 6. in the UDO laboratory in the ASSE mine (-925 m),

100000

10000

1000

100

Counts/(channel . 40000 s) 10

1 0 50 100 150 200 250 300 350 400 Channel Number (1 keV/channel)

Fig. 24: Spectra of background collected in different conditions (see text) we see that the deeper in the ground the lower background spectrum. But if a person is placed inside, the spectra in conditions 5 and 6 present the same intensity. This indicates that the efficacy of a shielded room has limited effect in the case of in vivo counting.

How to correctly reduce the background

The purpose is to eliminate the photopeaks by choosing materials free of contaminations (e.g. the 46.5 keV photopeak from 210Pb). To reduce the continuum, a detector with a volume optimised for a given photon energy should be chosen. Similarly, when multiple detectors are used in array, one of these detectors can be too distant to obtain a good peak/continuum ratio. This detector should be removed during the analysis. Finally, the use of active techniques such as anti- coincidence, pulse rise time discriminators and anti-cosmic gates can often be fruitful. we see that the deeper in the ground the lower background spectrum. But if a person is placed inside, the spectra in conditions 5 and 6 present the same intensity. This indicates that the efficacy of a shielded room has limited effect in the case of in vivo counting.

How to correctly reduce the background

The purpose is to eliminate the photopeaks by choosing materials free of contaminations (e.g. the 46.5 keV photopeak from 210Pb). To reduce the continuum, a detector with a volume optimised for a given photon energy should be chosen. Similarly, when multiple detectors are used in array, one of these detectors can be too distant to obtain a good peak/ continuum ratio. This detector should be removed during the analysis. Finally, the use of active techniques such as anti-coincidence, pulse rise time discriminators and anti-cosmic gates can often be fruitful.

246 CLASSIFICATION OF THE IN VIVO MEASUREMENTS

There are two ways to catalogue the in vivo counting procedures:

According to the part of the body that requires an examination or according to the radionuclides to detect. Both classifications are necessary because of the random aspect of the contamination and because a radionuclide can target a specific organ according to its physico-chemical state. Table 4 summarizes the different types of measurements encountered in WBC.

Examined radionuclides

1. Fission and activation products (nuclear reactor, particle accelerator) 2. Medical radionuclides: Iodines, 99mTc, 201Tl,… Adopted procedures

1. WBC: tilted chair 2. Organ measurements: Supine or prone position: detector –organ dependence 3. Thyroid measurement 4. Wound measurement 5. Metabolism – Scanning (study of new medicines)

Table 4: Synoptic of the different types of measurements encountered in WBC Note: Single measurement is sometimes not possible.

The Whole Body Counting (WBC)

This name implies the measurement of the radionuclides uniformly 247 distributed in the body. Different techniques are used: the “tilted chair”, the bed geometry, the arc geometry, the scanning bed, etc... The purpose is to collect the highest number of photons emitted by the investigated radionuclide in the body and the lowest background. As explained before, the choice of the analysis method depends on both the detector and the complexity of the spectrum. The WBC technique is used for most of the radionuclides encountered in the nuclear fuel cycle and in nuclear medicine. Nuclides excluded from this category are low energy photon emitters and radionuclides concentrating in target tissues.

An example of standard spectra analysis is given in the figure 25. The person is contaminated with 60Co but the measurement is complicated by the presence of 41Ar. 33

Fig. 25: Spectrum of a person contaminated with 60Co. Measurement of organs Measurement When of organs a radionuclide concentrates in a specific organ or tissue,

Whenthe measurement a radionuclide concentratesof this organ in a givesspecif icmore organ information or tissue, the thanmeasurement WBC. ofThis this 248organ givesis themore case information for the than iodine WBC. where This is 30% the case to for50% the ofiodine the where intake 30% concentrates to 50% of the intake concentratesin the thyroid in the andthyroid stays and staysthere ther withe with a biological a biological half-lifehalf-life of of 120 120 days, days, the otherthe fraction being eliminated in a few days. The assessment of the lung burden is another case of specific organother measurement:fraction being Inhalation eliminated is the in most a few important days. The mode assessment of contamination of the and lung the radioactiveburden particles is mayanother stay in case the tracheo-bronchi of specific organal system measurement: with a very long Inhalation biological half-life. is the 235-238 232-228 This is themost case importantfor U modeand for of contaminationTh. and the radioactive particles may Measurementstay in the tracheo-bronchial of wounds system with a very long biological half-life. This is the case for 235-238U and for 232-228Th. An accident (e.g. during the manipulation of radioactive materials in glove boxes) may produce an injury with contamination of the wound. This type of contamination is easy to identify and to quantify even Measurement for isotopes of plutonium.of wounds The contaminant is in fact near to the surface of the wound and is easily followed during the surgical operation. The measurement must be done as fast as possible to avoid An accident transfer of (e.g. the contaminanduring thet intomanipulation the system. of An radioactive example of materials a software developedin for glove the measurement boxes) may of produce contaminated an injury wounds with is given contamination in Fig. 26. of the wound. This type of contamination is easy to identify and to quantify even for isotopes of plutonium. The contaminant is in fact near to the surface of the wound and is easily followed during the surgical operation. The measurement must be done as fast as possible to avoid transfer of the contaminant into the system. An example of a software developed for the measurement of contaminated wounds is given in Fig. 26. 34

Fig. 26: Software developed for the analysis of a contaminated wound spectrum. 249 Whole Body Scanning Whole Body Scanning can be used to localise contamination in the body: In the counting room, the detector assembly must be hung on a funicular device that allows the detector to travel along the axis of symmetry of the body. An energy range also must be predefined. A stepper motor with adjustable speed produces the displacement of the detector. The person is on the bed in supine or prone position. This technique is useful for the study of metabolism of inhaled or ingested radionuclides. An example of a scanning can be seen on Fig. 27: A HPGe detector measuring the 661.6 keV line of 137Cs homogeneously distributed in the three tubes of an RMC plastic phantom (PMM). The two extreme position of the detector-collimator assembly is shown on the figure.

35

Whole Body Scanning

Whole Body Scanning can be used to localise contamination in the body: In the counting room, the detector assembly must be hung on a funicular device that allows the detector to travel along the axis of symmetry of the body. An energy range also must be predefined. A stepper motor with adjustable speed produces the displacement of the detector. The person is on the bed in supine or prone position. This technique is useful for the study of metabolism of inhaled or ingested radionuclides. An example of a scanning can be seen on Fig. 27: A HPGe detector measuring the 661.6 keV line of 137Cs homogeneously distributed in the three tubes of an RMC plastic phantom (PMM). The two extreme position of the detector-collimator assembly is shown on the figure.

RMC phantom: Scanning with collimator

9.00E-05

250 y 6.00E-05

Efficienc 3.00E-05

0.00E+00 -50 -30 -10 10 30 50 Detector longitudinal position

Fig. 27: Example of scanning result calculated with MCNPX code on a RMC PMM phantom (in collaboration with Dr V. Koukouliou, Dr. E. Carinou, GAEC-Athens) 35

Whole Body Scanning

Whole Body Scanning can be used to localise contamination in the body: In the counting room, the detector assembly must be hung on a funicular device that allows the detector to travel along the axis of symmetry of the body. An energy range also must be predefined. A stepper motor with adjustable speed produces the displacement of the detector. The person is on the bed in supine or prone position. This technique is useful for the study of metabolism of inhaled or ingested radionuclides. An example of a scanning can be seen on Fig. 27: A HPGe detector measuring the 661.6 keV line of 137Cs homogeneously distributed in the three tubes of an RMC plastic phantom (PMM). The two extreme position of the detector-collimator assembly is shown on the figure.

The measurements of selected radionuclides 36 Thorium in the lungs The measurements of selected radionuclides This element is commonly found in the earth’s crust and is Thorium in the lungs used in different industries: high-pressure light bulbs, electronics, glass Thismanufacturing, element is commonly in the found gas in the mantles, earth’s cr ustin andwelding is used in rods different and industries: in electric high- pressure light bulbs, electronics, glass manufacturing, in the gas mantles, in welding rods and in electricresistance. resistance. Thorium Thorium isis alsoalso used used as a astarg aet targetin X-rays in generators X-rays andgenerators as getter in andvacuum as tubesgetter and in in vacuumhigh-pressure tubes light and bulbs. in high-pressure light bulbs.

232Th 228Th 10 1.4 10 a 1.913 a 228Ac RMC phantom: Scanning with collimator 6.15 h 228Ra 224Ra 5.76 a 3.66 d 9.00E-05

220Rn y 6.00E-05 55.6 s 251

216 212 Efficienc 3.00E-05 Po Po 0.145 s 0.298 µs 212Bi 1.009 h 0.00E+00 212Pb 208Pb -50 -30 -10 10 30 50 208 10.6 h Tl stable Detector longitudinal position 3.053 min

Fig. 28: Radioactive family of 228Th/232Th. Fig. 27: Example of scanning result calculated with MCNPX code on a RMC PMM phantom 228 208 The nuclides Ac and Tl are the most easily measured for the assessment of thorium. Commentaire [SCK1] : thor (in collaboration with Dr V. Koukouliou, Dr. E. Carinou, GAEC-Athens) ium_family.xls

Commentaire [SCK2] : 120 Commentaire [SCK3] : thor 100 ium_family.xls 80 Ra-228 60 Th-228 Th-232

Activities(Bq) 40

20

0 0 10 20 30 40 50 Time after chemical separation (years) Commentaire [SCK4] : Thor 228 232 228 Fig.Fig. 29: 29:Evolution Evolution of the of activities the activities of Th,of 228Th,Th 232 andTh andRa 228withRa time.with time. ium-evolution.xls 232-228 228 Commentaire [SCK5] : TheThe initialinitial activities of of 232-228Th are 100100 BqBq and and 228RaRa is is 0. 0. Bq. Bq. In nature and also just after chemical separation, the thorium contains principally two isotopes, Commentaire [SCK6] : Thor ium-evolution.xls 228 As chemical separations remove Ra (T1/2 = 5.76 a), this equilibrium is disturbed. While 232Th- activity remains constant (Half-life = 14.1 109 a), the 228Th-activity (Half-life = 1.913 a) initially decreases. After 5 years, the ratio 228Th/232Th reaches a minimum value (0.42); afterwards, the ratio 228Th/232Th rises again and37 reaches 95 % of the equilibrium (Fig. 29) after 30 years and 99% after 40 years. The thorium must be measured in the 232Th and 228Th in equilibriumlungs before (and ita smallreaches fraction the ofsystem. 230Th and 234Th from the 238U family). The radioactive family of 232/228Th is given in Fig 28.

The thorium228 is considered as a very toxic element because232 of its As chemical separations remove Ra (T1/2 = 5.76 a), this equilibrium is disturbed. While Th- activity remains constantnephrotoxicity (Half-life = 14.1(similar 109 a), to the uranium, 228Th-activity it decreases (Half-life =the 1.913 glomerular a) initially filtration decreases. After 5 years,rate) the and ration because 228Th/232 Thof reachesits several a minimum daughters value (0.42); with afterwards,short half-lives, the ratio most of 228 232 Th/ Th rises againwhich and reaches being 95 -emitters.% of the equilibrium (Fig. 29) after 30 years and 99% after 40 years. The thorium must be measuredα in the lungs before it reaches the system.

The thorium is consideredDifferent as a very methods toxic element are used because to assess of its nephrotoxicity the thorium (similar in the tolungs: uranium, it decreases the glomerular filtration rate) and because of its several daughters with short half-lives, most of which being �-emitters. 1. In the first method, the concentrations of the isotopes of thorium in Different252 methods are usedthe to lungs assess arethe thoriumdetermined in the lungs:by the assessment of 208Tl, one of the last 1. In the first method, theradioactive concentrations daughters of the isotopes of the of family thorium (Fig. in the 30).lungs are determined by the assessment ofThis 208Tl, radionuclide one of the last radioactive emits a γ da-rayughters at 2.6of the MeV, family far (Fig. from 30). the 40K and its This radionuclide emitscontinuum. a �-ray at This 2.6 MeV, simple far techniquefrom the 40 K assumes and its continuum. the equilibrium This simple between all technique assumes thethe equilibrium members between of the familyall the members ignoring of the familypresence ignoring of an the inert presence gas, of the thoron an inert gas, the thoron (220Rn). It is partly exhaled during respiration. (220Rn). It is partly exhaled during respiration.

Fig. 30: Example of lung measurement for 232/228Th in the lung.

2. The second method uses the HPGe crystal (Fig. 31). The high resolution of this detector permits 38 2. The second method uses the HPGe crystal (Fig. 31). The high resolution theof analysisthis detector of the �permits-rays emitted the analysisby 228Ac. of the γ-rays emitted by 228Ac. 38 232 228 This technique technique does does not dependentnot depend on theon equilibriumthe equilibrium between between Th and 232 ThTh and and 228is notTh subject to 220 andsystematic is not errors subject due toto systematicRn exhalation. errors due to 220Rn exhalation. the analysis of the �-rays emitted by 228Ac. This technique does not dependent on the equilibrium between 232Th and 228Th and is not subject to systematic errors due to 220Rn exhalation. 2500 239 keV l 2000 583 keV 1500 2500 338 keV 511 keV 911 keV 239 keV

l 1000 2000 Counts/channe 583 keV 500 1500 338 keV 0 511 keV 911 keV 1000

Counts/channe 0 200 400 600 800 1000 500 Channel Number (1. keV/channel) 232/228 Fig.Fig. 31: 31: 0HPGe HPGe spectrum spectrum of of thorium thorium (232/228 ( Th)Th) in equilibrium in equilibrium with with its daughters its daughters. 0 200 400 600 800 1000 In thisthis case, case, a double a double planar planar HPGeChannel crystalHPGe Number will (1.crystal keV/channel) measure will the measure lungs with the counting lungs efficiencieswith and countingdetection limits efficiencies presented in and Table detection 5. The232/228 detecti limitson limits presented have been inobtained Table from 5. people The and with253 Fig. 31: HPGe spectrum of thorium ( Th) in equilibrium with its daughters. 40 detectionthe BOMAB limits phantom have filled been with obtained an aqueous from solution people of KCl and containing with the 4600 BOMAB Bq of K. In this case, a double planar HPGe crystal will measure the lungs with counting efficiencies and detectionphantom limits presented filled inwith Table an 5. Theaqueous Counting detecti efficienciesonsolution limits have of at beenKClDetection obtainedcontaining fromlimits people4600 for a 3000Bqand withof 40 228 the BOMABK. phantom filled with an aqueous338 solutionkeV ( Ac)of KCl containingsecond 4600 counting Bq of 40 timeK. (counts.s-1.Bq-1) (Bq) Detector Counting1 efficiencies(2.36 � 0.06) at 10-3Detection limits for a25 3000 228 Detector 2 338 keV(2.28 ( Ac)� 0.06) 10-3 second counting time25 -1 -1 (Bq) Detectors 1+2 (counts.s(4.64.Bq� 0.00)) 10-3 17 Detector 1 (2.36 � 0.06) 10-3 25 Detector 2 Table(2.28 5: Efficiencies� 0.06) 10-3 of the 20-mm HPGe25 detectors for 228 -1 -1 Detectors 1+2 the measurement(4.64 � 0.00) of 10-3 Ac in the lungs (in 17counts.s .Bq ).

220 3. The third Tabletechnique 5: Efficiencies is based on ofthe the measurement 20-mm HPGe of exhaleddetectors forRn (half-life=56 seconds). The measured theperson measurement breaths aged of 228airAc with in athe mask. lungs The (in counts.sexhaled-1 air.Bq is-1 ).directed through a metallic grounded chamber and through devices able to measure the flow-rate, the humidity and the 220 220 216 212 3. The third3.temperature. The technique third The techniqueis basednoble ongas theis based measurementRn decays on the inside ofmeasurement exhaled the chamber Rn of (half-life=56into exhaled Po and 220 seconds). RnPb. (half- A The negatively measuredcharged person collection breaths aged head aircollects with thesea mask. positively The exhaled charged air particles. is directed The throughcollection a metallichead is removed 216 groundedlife=56from chamber the chamberseconds). and through and The measured devicesmeasured from able 20 person to to measure 25 hours breaths thewith flow-rate,aged an alpha air spectrometer. thewith humidity a mask. and ThePo theemits an �- temperature.exhaledparticle The at noble air8.78 is MeV. gasdirected 220Rn decaysthrough inside a metallic the chamber grounded into 216 Pochamber and 212Pb. and A throughnegatively charged devicescollection able head tocollects measure these positivelythe flow-rate, charged the particles. humidity The collectionand the temperature.head is removed from the chamber and measured from 20 to 25 hours with an alpha spectrometer. 216Po emits an �- particle at 8.78 MeV. The noble gas 220Rn decays inside the chamber into 216Po and 212Pb. A negatively charged collection head collects these positively charged particles. The collection head is removed from the chamber and measured from 20 to 25 hours with an alpha spectrometer. 216Po emits an α-particle at 8.78 MeV.

Uranium in the lungs

Contamination with uranium is possible at every step of the fuel cycle: the mining, the milling, the fuel rod production, and the reprocessing. During mining the danger is associated with inhalation of the daughters of 222Rn: 214Pb and 214Bi and the 210Pb which are bone-seekers. During the milling and the concentration process, the most worrying nuclides are 230Th, 226Ra, 210Pb, 210Po.

The radium, concentrated in the slag heap, can be a high risk for the health 254 because of the 222Rn.

Uranium is a special case in the radiation protection of the workers: its danger is related to its nephrotoxicity instead of its radiation. The uranium decreases the glomerular filtration rate.

For this reason the body content of uranium is described in units of weight (mg) instead of activity (Bq). The natural body burden of natural uranium is 90 μg or 1.1 Bq.

The daily intake varies between 0.9 and 2.1 μg in water and between 1.3 and 3 µg in food. The industrial uranium, after chemical separation, contains three radionuclides contributing to lung dose after inhalation. 39

Uranium in the lungs

Contamination with uranium is possible at every step of the fuel cycle: the mining, the milling, the fuel rod production, and the reprocessing. During mining the danger is associated with inhalation of the daughters of 222Rn: 214Pb and 214Bi and the 210Pb which are bone-seekers. During the milling and the concentration process, the most worrying nuclides are 230Th, 226Ra, 210Pb, 210Po.

The radium, concentrated in the slag heap, can be a high risk for the health because of the 222Rn.

Uranium is a special case in the radiation protection of the workers: Its danger is related to its nephrotoxicity instead of its radiation. The uranium decreases the glomerular filtration rate.

For this reason the body content of uranium is described in units of weight (mg) instead of activity (Bq). The natural body burden of natural uranium is 90 �g or 1.1 Bq.

The daily intake varies between 0.9 and 2.1 �g in water and between 1.3 and 3 µg in food. The industrial uranium, after chemical separation, contains three radionuclides contributing to lung dose after inhalation.

Before enrichment, one gram of natural uranium contains three nuclides with the proportions presented in Table 6. Before enrichment, one gram of natural uranium contains three nuclides with the proportions presented in Table 6. Nuclide Half-life Abundance Activity / g uranium (a) (in 1 g uranium) kBq 238U 4.47 109 982.8 mg 12.1 235U 7.038 108 7.2 mg 0.57 234U 245400. 0.056 mg 12.8 Table 6: Composition of 1 g of natural uranium (25. kBq).

After inhalation, uranium stays in the lungs with a biological half- After inhalation, uranium stays in the lungs with a biological half-life of 1500 days. Differentlife techniques of 1500 aredays. used Different to determine techniques the uranium are body used burdens: to determine the static air the sampling uranium (SAS), the personalbody air burdens: sampling the (PAS), static the air urine sampling monitori ng, (SAS), but these the methods personal are airused sampling as trigger for further investigations by in vivo techniques. 238U does not emit �-rays but its direct daughter 234Th (PAS), the urine monitoring, but these methods are used as trigger238 for (half-life = 24.1 d) emits three photons at respectively 63.3 keV, 238 92.6 keV and 92.8 keV. U then further investigations234 by in vivo techniques. U does not emit γ-rays can be quantified from Th if the secular equilibrium is reached (95 % after four months) or if the 234 date ofbut extraction its direct is known. daughter Th (half-life = 24.1 d) emits three photons at respectively 63.3 keV, 92.6 keV and 92.8 keV. 238U then can be quantified 235 U emitsfrom the 234 followingTh if the photons: secular equilibrium is reached (95 % after four months) 255 � �-rays:or if 185.7the date keV of(54 extraction %), 143.8. keVis known. (11.1%), 163.3 keV (5.49%) and at 205. keV (5.77%) � X-rays: 90 keV (), at 93.5 (4.3%), at 105.4 keV (1.98%) and at 108.99 keV (0.66%). 235U emits the following photons: Its direct daughter, the 231Th also emits photons at 25.6 keV (14.8 %) and at 84.2 keV (6.5 %). 234U produces a weak �-peak at 53.23 keV (0.12 %), not visible with a NaI(Tl) detector because it is • γ-rays: 185.7 keV (54 %), 143.8. keV (11.1%), 163.3 keV (5.49%) and at 205. keV (5.77%) • X-rays: 90 keV (), at 93.5 (4.3%), at 105.4 keV (1.98%) and at 108.99 keV (0.66%).

Its direct daughter, the 231Th also emits photons at 25.6 keV (14.8 %) and at 84.2 keV (6.5 %). 234U produces a weak γ-peak at 53.23 keV (0.12 %), not visible with a NaI(Tl) detector because it is shaded by the peaks of the 234Th at 63.3 keV. 234U is the most dangerous because it is responsible for most of the dose to the lungs. Different techniques can be used for the assessment of the uranium in the lungs: • When measured with NaI(Tl), four energy ranges of the spectrum are examined. The energy ranges between 40 and 110 keV (around 93 keV) and between 168 and 214 keV(around 186 keV) are used for the 40 assay of 238U and 235U respectively. The other zones (132-166 keV and 220-270 keV) are used to determine the influence of other isotopes 234 234 shaded by(137 theCs peaks and 40ofK). the Th at 63.3 keV. U is the most dangerous because it is responsible for most of the dose to the lungs. Different techniques can be used for the assessment of the uranium in the• lungs:The measurement of uranium with proportional counters has been investigated to measure the X-rays between 10 and 20 keV but this � Whentechnique measured doeswith NaI(Tl),not yield four better energy results. ranges of the spectrum are examined. The energy ranges between 40 and 110 keV (around 93 keV) and between 168 and 214 keV(around 186 •keV) A are third used method for the assay is based of 238 Uon and the 235 Uuse respectively. of HPGe The semiconductor other zones (132-166 crystals keV and 220-270(see keV)Fig. are32). used to determine the influence of other isotopes (137Cs and 40K). � The measurement of uranium with proportional counters has been investigated to measure the X-rays between 10 and 20 keV but this technique does not yield better results. With a 12”x4” scintillator, the detection limit for natural uranium is 4 mg � A third method is based on the use of HPGe semiconductor crystals (see Fig. 32). (1.65σ), that is 2.2 Bq 235U and 49. Bq 238U. The measurement of uranium Withis anever 12"x4" easy scintillator, and the the results detection can limit be surprising. for natural uranium is 4 mg (1.65�), that is 2.2 Bq 235U and 49. Bq 238U. The measurement of uranium is never easy and the results can be surprising. 256

1200 63.3 keV (Th-234) ! 1000 143.8 keV (U-235) 800 92.6 keV (Th-234)!

600 185.7 keV (U-235) Counts/DE

400

200 163.3 keV (U-235)

0 0 50 100 150 200 250 300 350 400

Energy (keV) Fig. 32: Spectrum of natural uranium collected with a HPGe The most visible peaks are: 63.3 keV (234Th), 92.6 keV (234Th), The isotopes of the plutonium and the transuranics

Very toxic from a radiological41 point of view, the plutonium can be inhaled or ingested in fuel fabrication factories, in reprocessing plants, during waste treatment and in research laboratories. The systemic plutonium The isotopes of the plutonium and the transuranics is always measured by very sensitive urine analyses but the lung burden of insoluble Very toxic plutonium from a radiological must be point assessed of view, by the the plutonium direct method. can be inhaled The liver or ingested is in fuelalso fabrication an organ factories, to measure in reprocessing for incorporated plants, during plutonium waste treatment detection. and in research laboratories. The systemic plutonium is always measured by very sensitive urine analyses but the lung burden of insoluble plutonium must be assessed by the direct method. The liver is also an organ to measure for incorporated Plutonium plutonium detection.in the lungs

Plutonium in the lungs The assessment of 239Pu in the lungs is a valuable complement to systemic The assessment measurements. of 239Pu inThe the isotopes lungs is a ofvaluable plutonium complement are α to-emitters systemic (exceptmeasurements. The241 isotopesPu). Their of plutonium characteristics are �-emitters are given (except in 241 TablePu). Their 7. characteristics are given in Table 7.

238 239 240 241 242 Radionuclide Pu Pu Pu Pu Pu Type of decay � � � � � 257 Half-life (y) 87.7 24110 6563 14.4 376300 X-ray Intensity (%) 13 3.6 12 - 10 Table 7: Characteristics of the isotopes of plutonium.

239239 235 Pu Puis detected is detected by U-X byL U-Xrays emittedL rays emittedafter the internalafter the conversion internal of conversion the daughter of U. The 235 emittedthe daughter energies are 13.6,U. The 16.9 emitted and 20.2 energies keV. But are the 13.6,weak X16.9L rays and are 20.2strongly keV. absorbed But in the tissues.the weakFor this X reason, rays arethe morphologicalstrongly absorbed parameters in the (CWT) tissues. of the For measured this reason, person theare important factorsL in determining the lung burden. The ribs stop about 50 % of the X-rays emitted towardsmorphological the detector butparameters recent studies (CWT) show of that the the measured cartilage linking person the are ribs important to the sternum doesfactors not completely in determining stop the X-raysthe lung indicating burden. th atThe exploration ribs stop of aboutthis part 50 of % the of tracheo- the bronchialX-rays zone emitted may be towards useful. the detector but recent studies show that the cartilage linking the ribs to the sternum does not completely stop the X- The plutonium burden can be measured with proportional Counter, with phoswich detectors or withrays planar indicating HPGe thatdetector exploration arrays. of this part of the tracheo-bronchial zone may be useful. In order to improve the efficiency of the lung counting, a new approach of the problem was 241 239 used, based Theon the plutonium detection of burden Am as can tracer. be measured Most of the with time, proportionalthe Pu is not Counter, pure but present with other plutonium radionuclides: The radionuclides 238Pu, 239Pu, 240Pu and 242Pu are �-emitters, with241 phoswich detectors or with planar HPGe detector arrays. but Pu is a �-emitter with a short half-life (14.3 a).

The "specific" activity of 241Pu is much greater than that of 239Pu and its daughter 241Am (T ½ = 432.7 a) emits a �-ray at 59.54 keV (with an intensity of 35.9 %) easier to detect than 239Pu.

The measurement of americium can be performed with a thin NaI(Tl) crystal, a phoswich detector or a HPGe planar detector. For instance, with a total sensitive area of 5775 mm², a detection limit 241 (LC) of 3 to 10 Bq Am in the lungs can be obtained with a HPGe detector (Fig. 33). This technique is possible only if the isotopic composition of the contaminant is known. Another advantage of the semiconductor detectors is the reduced Compton effect from 40K, 137Cs or other isotopes as well as from the background still existing in the counting room. In order to improve the efficiency of the lung counting, a new approach of the problem was used, based on the detection of 241Am as tracer. Most of the time, the 239Pu is not pure but present with other plutonium radionuclides: The radionuclides 238Pu, 239Pu, 240Pu and 242Pu are α-emitters, but 241Pu is a β-emitter with a short half-life (14.3 a).

The “specific” activity of 241Pu is much greater than that of 239Pu and its daughter 241Am (T ½ = 432.7 a) emits a γ-ray at 59.54 keV (with an intensity of 35.9 %) easier to detect than 239Pu.

The measurement of americium can be performed with a thin NaI(Tl) crystal, a phoswich detector or a HPGe planar detector. For instance, with a 241 total sensitive area of 5775 mm², a detection limit (LC) of 3 to 10 Bq Am in the lungs can be obtained with a HPGe detector (Fig. 33). This technique is possible only if the isotopic composition of the contaminant is known. Another advantage of the semiconductor detectors is the reduced Compton 258 effect from 40K, 137Cs or other isotopes as well as from the background still existing in the counting room. The characteristics of the Lung Counter commented here are described in Table 7.6. 42

Fig. 33: Measurement of 241Am in the lungs with a double planar HPGe The characteristics of the Lung Counter crystalcommented here are described in Table 7.6.

Fig. 33: Measurement of 241Am in the lungs with a double planar HPGe crystal

The effect of attenuation is especially important in the low energy range as shown in Fig. 34. Summerling calculates the thickness of these tissues from morphological parameters (age, height, weight and thorax perimeter) with empirical formulae such as the following:

W E S = 0.1 � (1.33 - 0.04 Age - 1) H 2

(ES = chest wall tissue thickness in cm, Age in years, H = height in m, W = weight in kg.

The correlation of the measured photopeaks and the calculated attenuation provides an estimation of the chest wall thickness with a better accuracy and is also applicable for female subjects. Another solution is the use of ultra-sonic sensor for the direct measurement of the CWT.

1.00E+00

1.00E-01 59.5 keV meas 59.5 keV calc 26 keV meas 26 keV calc 1.00E-02 21 keV meas 21 keV calc 17 keV meas 1.00E-03 17 keV calc

1.00E-04 10.0 15.0 20.0 25.0 30.0 35.0 40.0

Fig. 34: Effect of the chest wall thickness on the efficiency of a double HPGe detector. The analysis of 241Am with planar HPGe crystals is shown in Fig. 35. 42

The characteristics of the Lung Counter commented here are described in Table 7.6.

Fig. 33: Measurement of 241Am in the lungs with a double planar HPGe crystal

42

The characteristics of the Lung Counter commented here are described in Table 7.6.

Fig. 33: Measurement of 241Am in the lungs with a double The planar effect HPGe of attenuationcrystal is especially important in the low energy range as shown in Fig. 34. Summerling calculates the thickness of these tissues The effect of fromattenuation morphological is especially parameters important in (age, the low height, energy weight range andas shown thorax in perimeter)Fig. 34. Summerling calculates the thickness of these tissues from morphological parameters (age, height, weight and thoraxwith perimeter) empirical with formulae empirical such formulae as the such following: as the following:

W E S = 0.1 � (1.33 - 0.04 Age - 1) H 2

(ES = chest wall(E Stissue = chest thickness wall intissue cm, Age thickness in years, in H cm, = height Age inin m, years, W = weightH = height in kg. in m, W = weight in kg). The correlation of the measured photopeaks and the calculated attenuation provides an The effect of attenuation is especially important in the low energy range as shown in Fig. 34. estimation of the chest wall thickness with a better accuracy and is also applicable for female Summerling calculates the thickness of these tissues from morphological parameters (age, height, subjects. Another solution The is the correlation use of ultra-soni of thec sensor measured for the directphotopeaks measurement and theof the calculated CWT. weightattenuation and thorax perimeter) provides with an estimationempirical formulae of the suchchest as wall the following: thickness with a better 1.00E+00accuracy and is also applicable for femaleW subjects. Another solution is the E S = 0.1 � (1.33 - 0.04 Age - 1) use of ultra-sonic sensor for the direct Hmeasurement2 of the CWT.

1.00E-01 59.5 keV meas (ES = chest wall tissue thickness in cm, Age in years, H = height in m, W = weight in kg. 59.5 keV calc 26 keV meas 259 The correlation of the measured photopeaks and the calculated26 keV calc attenuation provides an 1.00E-02 estimation of the chest wall thickness with a better accuracy and21 is keV also meas applicable for female subjects. Another solution is the use of ultra-sonic sensor for the direct21 keV measurement calc of the CWT. 17 keV meas 1.00E-03 17 keV calc 1.00E+00

1.00E-04 10.01.00E-01 15.0 20.0 25.0 30.0 35.0 40.0 59.5 keV meas 59.5 keV calc Fig. 34: Effect of the chest wall thickness on the efficiency of a double HPGe26 detector. keV meas 241 26 keV calc The analysis1.00E-02 of Am with planar HPGe crystals is shown in Fig. 35. 21 keV meas 21 keV calc 17 keV meas 1.00E-03 17 keV calc

1.00E-04 10.0 15.0 20.0 25.0 30.0 35.0 40.0

Fig. 34: Effect of the chest wall thickness on the efficiency of a double HPGe detector. The analysis of 241Am with planar HPGe crystals is shown in Fig. 35. 42

The characteristics of the Lung Counter commented here are described in Table 7.6.

Fig. 33: Measurement of 241Am in the lungs with a double planar HPGe crystal

The effect of attenuation is especially important in the low energy range as shown in Fig. 34. Summerling calculates the thickness of these tissues from morphological parameters (age, height, weight and thorax perimeter) with empirical formulae such as the following:

W E S = 0.1 � (1.33 - 0.04 Age - 1) H 2

(ES = chest wall tissue thickness in cm, Age in years, H = height in m, W = weight in kg.

The correlation of the measured photopeaks and the calculated attenuation provides an estimation of the chest wall thickness with a better accuracy and is also applicable for female subjects. Another solution is the use of ultra-sonic sensor for the direct measurement of the CWT.

1.00E+00

1.00E-01 59.5 keV meas 59.5 keV calc 26 keV meas 26 keV calc 1.00E-02 21 keV meas 21 keV calc 17 keV meas 1.00E-03 17 keV calc

1.00E-04 10.0 15.0 20.0 25.0 30.0 35.0 40.0

TheFig. 34:analysis Effect of the241 Amchest with wall thicknessplanar HPGe on the crystalsefficiency is of shown a double in HPGe Fig. 35.detector. The analysis of 241Am with planar HPGe crystals is shown in Fig. 35.

Fig. 35: Analysis of a lung spectrum for the assessment of 241Am in the 260 lungs with the Spitz method

Plutonium in wounds

The contamination of a wound can present a high health risk if actinide is present. An immediate intervention is required. Special methods have been developed to detect and measure the contamination with small detectors able to reach zones of the body difficult to access (e.g. between the fingers). When the wound is open or near to the skin, the X-rays from plutonium are easily detected with a thin NaI(Tl) detector. Limits of detection less than 5 Bq are possible in a fifteen minute count. The use of a HPGe crystal is still better in this case because of its resolution. Fig. 36 shows the spectrum of a wound contaminated with 239Pu and 241Am. On the same figure the spectrum obtained after the first surgical intervention (thick line) is shown. 43

Fig. 35: Analysis of a lung spectrum for the assessment of 241Am in the lungs with the Spitz method

Plutonium in wounds

The contamination of a wound can present a high health risk if actinide is present. An immediate intervention is required. Special methods have been developed to detect and measure the contamination with small detectors able to reach zones of the body difficult to access (e.g. between the fingers). When the wound is open or near to the skin, the X-rays from plutonium are easily detected with a thin NaI(Tl) detector. Limits of detection less than 5 Bq are possible in a fifteen minute count. The use of a HPGe crystal is still better in this case because of its resolution. Fig. 36 shows the spectrum of a wound contaminated with 239Pu and 241Am.. On the same figure the spectrum obtained after the first surgical intervention (thick line) is shown.

2000 59.5 keV 1600 X-rays 1200

800 Counts/channel 400 26. keV

0 0 100 200 300 400 Channel Number (0.2 keV/channel)

Fig. 36: Measurement of a wound, contaminated with Pu and Am. Fig. 36: Measurement of a wound, contaminated with Pu and Am. Scintillation detectors work at room temperature and can be very small but suffer from low resolution. Also the efficiency Scintillation of a NaI(Tl) detectors worsens with work time at because room of temperature the degradation and of silicone can be grease (optical contact between crystal and photomultiplier tube) and/or to humidity introduced in very small but suffer from low resolution. Also the efficiency of a NaI(Tl) worsens with time because of the degradation of silicone grease (optical 261 contact between crystal and photomultiplier tube) and/or to humidity introduced in the can containing the crystal. For this reason, the use of Ge detector is preferred when possible. The efficiency calibration of the Ge crystal is made just before or after the measurement of the wound. The comparison of the full energy peaks of the X-rays and γ-rays allows better precision and accuracy. A calibrated source of a Pu isotope deposited on the surface of a metal plate is measured in the same geometrical conditions as the wound. In case of a deep wound, a calculation of the attenuation may be necessary. Fig. 37 presents a screen shot of a program calculating the activity in a wound: the data furnished by the spectrum are used for wound contamination calculation. 44

the can containing the crystal. For this reason, the use of Ge detector is preferred when possible. The efficiency calibration of the Ge crystal is made just before or after the measurement of the wound. The comparison of the full energy peaks of the X-rays and �-rays allows better precision and accuracy. A calibrated source of a Pu isotope deposited on the surface of a metal plate is measured in the same geometrical conditions as the wound. In case of a deep wound, a calculation of the attenuation may be necessary. Fig. 37 presents a screen shot of a program calculating the activity in a wound:Now the room data temperaturefurnished by the semiconductor spectrum are used detectors for wound contamination (Silicon, CdZnTe calculation. or HgBrI ) have been used for the measurement of wounds contaminated with Now room2 temperature semiconductor detectors (Silicon, CdZnTe or HgBrI2) have been used for theactinides. measurement They of woundsshow very contaminated good results with (goodactinides. resolution They show and very low good detection results (good resolutionlimits) and and low can detection be very limits) small. and can be very small.

262

Fig. 37: Analysis of a contaminated wound (241Am).

Metabolism of plutonium Metabolism of plutonium The chemical properties of plutonium are extremely complex and chemical form greatly influences its Themetabolism. chemical The properties burden of ofPu plutoniumand Th in diffe arerent extremely organs are complex different and because chemical of different metabolic compartments. This was named the "liver problem" in 1944. The recent I.C.R.P. models considerform that greatly after inhalation, influences a radionuclide its metabolism. and its daughters The burden follow a ofsame Pu metabolism. and Th inThe liver is adifferent special organ organs because are differentafter inhalation because or ingestion, of different a large metabolic fraction of compartments. plutonium or actinides concentrateThis was there named with athe very “liver long retention problem” hal f-timein 1944. (40 a).The It isrecent easy to I.C.R.P. measure themodels liver 241Am burdenconsider but with that a slightly after inhalation,higher detection a radionuclide limit than in the and lungs. its daughters follow a

samePlutonium metabolism. in the The skull liver is a special organ because after inhalation or ingestion, a large fraction of plutonium or actinides concentrate there with Thea skullvery and long the retention patella are half-time thin bone. It(40 is possiblea). It is toeasy detect to oldmeasure contamination the liver with 241 radiumAm and burden but with a slightly higher detection limit than in the lungs. Plutonium in the skull

The skull and the patella are thin bone. It is possible to detect old contamination with radium and actinides by measuring these bones. 210Pb also can be measured in skull and in the patella to determine the exposure to radon progeny.

Radionuclides of iodine

The cases of contamination with iodine are numerous: 1. Production workers and medical people using iodine radionuclides (123,124,125,131I), 2. Persons contaminated during an accident in a power reactor with release of water from the primary circuit: 131,132,133I 3. Workers in a reprocessing plant: 129,131I.

Iodine is rapidly dispersed in the air and can be inhaled; it may also be 263 ingested, e.g. by drinking contaminated milk and by eating contaminated foodstuffs. The high radiotoxicity of the iodine radionuclides is due to its biological half-life (120 days) and because most of the contaminant concentrates in the thyroid.

The measurement of this organ can be done with a small NaI(Tl) detector placed near to the throat (results with a Ld less than 40 Bq after a 10 minute for 131I).

Different isotopes of iodine are now used in nuclear medicine (123I, 125I...) for diagnostic or therapeutic purposes. The isotopes emitting low energy X- or γ-rays are difficult to measure with a NaI(Tl) detector. Now, HPGe semiconductor detectors give much better results due to the high resolution and the easy identification of the photo-peaks. Examples are given in Fig. 38 and 39. 45

210 actinides by measuring these bones. Pb also 45can be measured in skull and in the patella to determine the exposure to radon progeny.

actinides Radionuclides by measuring of these iodine bones. 210Pb also can be measured in skull and in the patella to determine the exposure to radon progeny. The cases of contamination with iodine are numerous: 123,124,125,131 1. Production Radionuclides workers of iodine and medical people using iodine radionuclides ( I), 2. Persons contaminated during an accident in a power reactor with release of water from The casesthe of primarycontamination circuit: with 131,132,133 iodineI are numerous: 123,124,125,131 3.1.Workers Production in a workersreprocessing and medicalplant: 129,131 peopleI. using iodine radionuclides ( I), 2. Persons contaminated during an accident in a power reactor with release of water from Iodine is rapidlythe primary dispersed circuit: in the 131,132,133 air and canI be inhaled; it may also be ingested, e.g. by drinking contaminated3. Workers milk and in aby reprocessing eating contaminated plant: 129,131 foodsI. tuffs. The high radiotoxicity of the iodine radionuclides is due to its biological half-life (120 days) and because most of the contaminant concentratesIodine is rapidly in the dispersed thyroid. in the air and can be inhaled; it may also be ingested, e.g. by drinking contaminated milk and by eating contaminated foodstuffs. The high radiotoxicity of the iodine Theradionuclides measurement is dueof this to organits biological can be done half-life with (120a small days) NaI(Tl) and detectorbecause placedmost of near the to contaminant the throat 131 (resultsconcentrates with a inLd theless thyroid. than 40 Bq after a 10 minute for I).

The measurement Different isotopes of this of organ iodine can are be now done used with in anuclear small NaI(Tl) medicine detector (123I, 125 placedI...) for near diagnostic to the throat or 131 therapeutic(results with purposes. a Ld less The than isotopes 40 Bq emitting after a 10 low minute energy for X- orI). �-rays are difficult to measure with a NaI(Tl) detector. Now, HPGe semiconductor detectors give much better results due to the high resolution Different and the easyisotopes identification of iodine are of thenow photo- used inpeaks. nuclear Examples medicine are (123 givenI, 125 inI...) Fig. for 38 diagnostic and 39. or therapeutic purposes. The isotopes emitting low energy X- or �-rays are difficult to measure with a NaI(Tl) detector.100 Now, HPGe semiconductor detectors give much better results due to the high resolution and the easy identification of the photo-peaks. Examples are given in Fig. 38 and 39. 80 2

100 60 3 1 80 2 40 4 Counts/channel 5 2060 3 1 40 0 4 Counts/channel 20 25 30 35 405 45 50 55 60 20 Photon Energy (keV) 129 0 Fig. 38:38: SpectrumSpectrum of of 129 I measuredI measured in in the the thyroid. thyroid. 20 25 30 35 40 45 50 55 60 The first one Theis the first spectrum one ofis athe person spectrum withPhoton 11 ofBq Energy aof person 129 (keV)I in the with thyroid. 11 Bq The of acquisition 129I in the time thyroid. was 129 129 7 1800 seconds and the detectionFig. 38: limit Spectrum was L Cof = 0.2I measured Bq. I hasin the a half-lifethyroid. of 1.57 10 years and The acquisition time was 1800 seconds and the detection limit was LC = decays with the emission129 of X-rays (1: 29.461 keV, 20.4 %7 - 2: 29.782 keV, 37.8 % -3: 33.606 keV, 0.2 Bq. I has a half-life of 1.57 10129 years and decays with the emission 10.2The % first - 4:34.606 one is the keV, spectrum 7.5 %) of and a person a �-ray with at 39.57111 Bq of keV Iwith in the an thyroid. intensity The of acquisition7.5 % (5). timeFig. 39was of X-rays 131(1: 29.461 keV, 20.4 % - 2: 29.782129 keV, 37.8 % -3: 33.6067 keV, presents1800 seconds the spectrum and the of detection I measured limit inwas the L thyroidC = 0.2 phantomBq. I displayedhas a half-life in Fig. of 14 1.57 (bottom-right). 10 years and decays with10.2 the emission % - 4:34.606 of X-rays keV, (1: 29.461 7.5 %) keV, and 20.4 a γ %-ray - 2: at29.782 39.571 keV, keV 37.8 with% -3: an33.606 intensity keV, 26410.2 % - 4:34.606of 7.5 %keV, (5). 7.5 Fig. %) and39 apresents �-ray at 39.571the spectrum keV with of an 131 intensityI measured of 7.5 in% the(5). Fig.thyroid 39 12000 131 presents thephantom spectrum ofdisplayed I measured in Fig. in the 14 46thyroid (bottom-right). phantom displayed in Fig. 14 (bottom-right).

800012000 364.8 keV

40008000 Counts/channel

4000

Counts/channel 0 0 100 200 300 400 Photon Energy (keV) 0 0 100 200 300 400 Photon Energy (keV)

131 Fig. 39: Spectrum of I measured in the thyroid phantom. Commentaire [SCK7] : p2i1 Fig. 39: Spectrum of 131I measured in the thyroid phantom. 31ca.xls The photopeak at 364.483. keV (81.2 %) of 131I (Half-life = 8.04 d) is used for the measurement of the thyroid burden.

Measurement of pure �-emitters

The slowing-down of electrons emitted by �-emitters in the body causes the emission of a continuous low-energy photon spectrum (the "Bremsstrahlung" radiation). The intensity of this spectrum depends on the atomic numbers of the matters in which it is generated (bones, soft tissues,...). These photons can be measured with a NaI(Tl) detector only if the least square fitting is used for the analysis. But the detection limit is quite high and varies with the radionuclide so that only high burdens of high �-max energy emitters can be measured (e.g. 90Sr/90Y, 32P, 33P, 35S,...). 90 This can be a problem for Sr (T1/2 = 28.78 a) because it concentrates in bone and accurate assessment by direct methods (see 90Sr and 89Sr) is difficult.

Study of metabolism

More and more studies of metabolism involve the use of labelled molecules. According to the type of investigation, the detector is selected for its sensitivity, its energy resolution or its spatial resolution (gamma-camera). A scintillation camera has been used in Brazil for the measurement of 99mTc in the tibia and fibula of persons treated with 99mTc-MDP (methylene diphosphonate). It is excellent for burden assessment (counting efficiency of 500 Bq per cpm) and can be used to image the bones and study the metabolism of the molecule in the whole skeleton. Another group from Göteborg, Sweden, employs a NaI(Tl) scintillator with a collimator to localise contamination for radiation protection purposes but also for profile measurement after surgery of patients with thyroid cancer. Before the treatment with 131I, the patient is given a low dose of 131I to test the uptake in the thyroid and to look for metastases in the rest of the body.

Lymph nodes The photopeak at 364.483. keV (81.2 %) of 131I (Half-life = 8.04 d) is used for the measurement of the thyroid burden.

Measurement of pure β-emitters

The slowing-down of electrons emitted by β-emitters in the body causes the emission of a continuous low-energy photon spectrum (the “Bremsstrahlung” radiation). The intensity of this spectrum depends on the atomic numbers of the matters in which it is generated (bones, soft tissues,...). These photons can be measured with a NaI(Tl) detector only if the least square fitting is used for the analysis. But the detection limit is quite high and varies with the radionuclide so that only high burdens of high β-max energy emitters can be measured (e.g. 90Sr/90Y, 32P, 33P, 35S,...). 90 This can be a problem for Sr (T1/2 = 28.78 a) because it concentrates in bone and accurate assessment by direct methods (see 90Sr and 89Sr) is difficult. 265 Study of metabolism

More and more studies of metabolism involve the use of labelled molecules. According to the type of investigation, the detector is selected for its sensitivity, its energy resolution or its spatial resolution (gamma-camera). A scintillation camera has been used in Brazil for the measurement of 99mTc in the tibia and fibula of persons treated with 99mTc-MDP (methylene diphosphonate). It is excellent for burden assessment (counting efficiency of 500 Bq per cpm) and can be used to image the bones and study the metabolism of the molecule in the whole skeleton. Another group from Göteborg, Sweden, employs a NaI(Tl) scintillator with a collimator to localise contamination for radiation protection purposes but also for profile measurement after surgery of patients with thyroid cancer. Before the treatment with 131I, the patient is given a low dose of 131I to test the uptake in the thyroid and to look for metastases in the rest of the body. Lymph nodes

After an incident involving the contamination of a wound, prompt intervention is recommended to avoid the transfer of the contaminants to the system of the subject. After intervention, the contamination may not be completely removed. The use of chelating products (e.g. Zn-DTPA) can aid the elimination of the contamination.47 The measurement of axillar lymph nodes (in case of hand injuries) can be useful to assess the associated remainingAfter an contamination. incident involving After the a contamination lung contamination, of a wound, the promptassessment intervention of is recommendedthe mediastinum to avoid lymph the transfer nodes of is therecommended. contaminants to the system of the subject. After intervention, the contamination may not be completely removed. The use of chelating products (e.g. Zn-DTPA) can aid the elimination of the contamination. The measurement of axillar lymph nodes (in case of handMeasurement injuries) can beof usefulthe knee to asse andss the the associated skull remaining contamination. After a lung contamination, the assessment of the mediastinum lymph nodes is recommended. Thin bones in proximity of the skin can be examined to assess Measurement of the knee and the skull old contamination by heavy metals (210Pb, 239Pu, 241Am,...) emitting low energy Thin photons. bones in proximity An example of the ofskin knee can bephantom examined is to shown assess oldin contaminationFig. 40. where by heavy 266 metalsthe (counting210Pb, 239 Pu,is made241Am,...) with emitting a CdZnTe low energyroom temperaturephotons. An example detector. of knee phantom is shown in Fig. 40. where the counting is made with a CdZnTe room temperature detector.

Fig. 40: Knee phantom measured with aCdZnTe detector

Medical applications of radionuclides

Many radionuclides produced48 by reactors (fission products and activation products) or by particle accelerators are used according to their chemicalMedical applicationsproperties, ofthe radionuclides radiation they emit and their half-life. Most of them are used in labelled molecules (about 300) allowing non-invasive Many radionuclides produced by reactors (fission products and activation products) or by particlestudies accelerators of tissues are used or accordi organs.ng to Normally their chemical the properties, half-life th ofe radiation the radionuclides they emit and their half-life.used Most is veryof them short are used as in shown labelled in mo Tablelecules 8 (about where 300) the allowing applications non-invasive are studies also of tissuesmentioned. or organs. Normally But they the can half-life contain of the longer radionuclides lived impurities used is very atshort production as shown in and Table x where the applications are also mentioned. But they can contain longer lived impurities at 123 productionnot separable. and not separable. This is This the iscase the case for forI 123 whichI which can can be be produced with with about about 1 % of1 125I that has% ofa half-life 125I that of has60.14 a half-lifedays. of 60.14 days.

Radionuclide Half-life Transition Applications 201 Tl 3.039 d E.C. Heart and thyroid examination. 131 I 8.02 d Follow-up of thyroid carcinomas, for therapy of goitre, hyperthyroid and thyroid carcinomas. 123 - 267 I 13.2 h � Follow-up of thyroid 99 99m - Mo/ Tc 2.7476 d/6.01 h � / IT Versatile isotope. 81m Kr 13.1sec IT Follow-up of lung ventilation and pulmonary embolism. 67 Ga 3.261 d E.C. Cancer diagnosis, labelled molecules 11C 20.3 m �+ Radionuclide for PET applications, Imaging of the brain 13N 9.97 m �+ Radionuclide for PET applications, Studies on the heart 15O 122.3 s �+ Radionuclide for PET applications, Studies on oxygen 18F 1.8296 h �+ Radionuclide for PET applications, Studies on epilepsy. 103 Pd 16.99 d E.C. Local treatment of prostate cancer. 43 - K 22.6 h � Metabolism of potassium, Hart muscle scintigraphy. 90Sr/90Y 28.78 a /(3.19h, 2.67 d) �-/ IT, �- Cardiovascular brachytherapy 32P 14.28d Cardiovascular brachytherapy 192Ir 240 a / 73.83 d IT, �- Cardiovascular brachytherapy 111In 67 h IT, �- Studies of the brain

Table 8: Some of the radionuclides used in medical applications

Because of the low energy photons it emits and its short half-life (60.14 d), 125I is used for therapeutic purposes e.g. in the treatment of the eye "sarcomas". This isotope has several emitted photons: X-rays at 27.202 keV (40.5 %), 27.472 keV (75.6 %), 30.98 keV (20.1 %) and 31.877 keV (4.38 %), and a �-ray at 35.49 keV (6.66 %). 125I is produced in accelerators by the reaction Because of the low energy photons it emits and its short half-life (60.14 d), 125I is used for therapeutic purposes e.g. in the treatment of the eye “sarcomas”. This isotope has several emitted photons: X-rays at 27.202 keV (40.5 %), 27.472 keV (75.6 %), 30.98 keV (20.1 %) and 31.877 keV (4.38 %), and a γ-ray at 35.49 keV (6.66 %). 125I is produced in accelerators by the reaction 125Te(d,2n)125I.

The radionuclides in Table 8 are used for two purposes: radiodiagnostics and radiotherapy. In cardiovascular brachytherapy for instance, high activity (≈ 4 1011 Bq) sources of 90Sr/90Y, 32P or 192Ir are used to deliver doses of 15 - 20 Gy to inhibit the formation of scar tissue after a patient undergoes a balloon angioplasty.

In case of accidental intake, an in vivo measurement may be necessary. The weak energy of the emitted photons creates detection problems when classical scintillation techniques are used to measure personal using these 268 radionuclides (physicians, nurses, patients and technicians). The semi- conductor detectors are best used here and permit the measurement of internal contamination. In the case of iodine, the isotope concentrates in the thyroid and a measurement with a detection limit of 100 Bq is easily done in a few minutes with a small HPGe detector.

Fast Whole Body Counting

Sometimes, when the required accuracy is not so high, fast WBC can be used (e.g. in emergency situation or in accidental situation when a large number of persons must be measured in a short time. Many devices have been developed to check workers when they exit a controlled zone. These machines are easy to use and give a “go/no go” result after less than one minute counting but a classical counting room can also be used for this purpose (Fig. 41). The advantage of the linear least square fitting is in this case obvious. 49

125Te(d,2n)125I.

The radionuclides in Table 8 are used for two purposes: radiodiagnostics and radiotherapy. In cardiovascular brachytherapy for instance, high activity (� 4 1011 Bq) sources of 90Sr/90Y, 32P or 192Ir are used to deliver doses of 15 - 20 Gy to inhibit the formation of scar tissue after a patient undergoes a balloon angioplasty.

In case of accidental intake, an in vivo measurement may be necessary. The weak energy of the emitted photons creates detection problems when classical scintillation techniques are used to measure personal using these radionuclides (physicians, nurses, patients and technicians). The semi- conductor detectors are best used here and permit the measurement of internal contamination. In the case of iodine, the isotope concentrates in the thyroid and a measurement with a detection limit of 100 Bq is easily done in a few minutes with a small HPGe detector.

Fast Whole Body Counting

Sometimes, when the required accuracy is not so high, fast WBC can be used (e.g. in emergency situation or in accidental situation when a large number of persons must be measured in a short time. Many devices have been developed to check workers when they exit a controlled zone. These machines are easy to use and give a "go/no go" result after less than one minute counting but a classical counting room can also be used for this purpose (Fig. 41). The advantage of the linear least square fitting is in this case obvious.

Fig. 41: Spectrum of WBC for a 30-second counting. Fig. 41: Spectrum of WBC for a 30-second counting.

Contamination in the non nuclear industry Contamination in the non nuclear industry Industries can be classified into three different parts: The Nuclear Sector (power plants, extraction and production of fuel, reprocessing 269 plants, waste management plants). The non-nuclear sector (non-nuclear industries making use of ionizing radiation: radiology, nuclear medicine, radiotherapy and scientific research). The non-nuclear industry involves the non-nuclear installations working without nuclear products. It was discovered that these industries could be a source of irradiation and contamination of workers because of natural radioactive materials present in high concentrations (Naturally Occurring Radioactive Materials or NORM’s are phosphates, the ferrous and non-ferrous minerals, glass, ceramic’s,...). These NORM’s can be sources of high doses and a high level of contamination. The concerned radionuclides are the families of 238U, 235U, 232Th and the products that can be found in the body are 222Rn, 210Po, 210Pb, 210Bi, 226Ra. The most important is probably thorium which is found in different industries. 50

Industries can be classified into three different parts: The Nuclear Sector (power plants, extraction and production of fuel, reprocessing plants, waste management plants). The non-nuclear sector (non-nuclear industries making use of ionizing radiation: radiology, nuclear medicine, radiotherapy and scientific research). The non-nuclear industry involves the non-nuclear installations working without nuclear products. It was discovered that these industries could be a source of irradiation and contamination of workers because of natural radioactive materials present in high concentrations (Naturally Occurring Radioactive Materials or NORM's are phosphates, the ferrous and non-ferrous minerals, glass, ceramic's,...). These NORM's can be sources of high doses and a high level of contamination. The concerned radionuclides are the families of 238U, 235U, 232Th and the products that canEMERGENCY be found in the bodyPREPAREDNESS are 222Rn, 210Po, 210ANDPb, 210INTERNALBi, 226Ra. The most important is probably thoriumCONTAMINATION which is found in differentMONITORING industries.

EMERGENCY PREPAREDNESSAn incident ANDresulting INTERNAL in the contamination CONTAMINATION of a person or a group of the MONITORING population always requires the ability to respond to the emergency. The preparedness for a singular contamination accident is similar from the An incident resulting inpoint the contamination of view of theof a personmaterial or a but group differs of the inpopulation the procedural always requires aspect. When an the ability to respond to the emergency. The preparedness for a singular contamination accident is similar from the point ofaccident view of the occurs material far but from differs the in thelaboratory, procedural aaspect. portable When measurement an accident system occurs far from the laboratory,as shown a portablein Fig. 42measur is requiredement system (detector, as shown module in Fig. with 42 is high required voltage power (detector, module withsupply, high voltage amplifier, power supplMCAy, amplifier,and a computer MCA and ). a computer ).

270

Fig. 42: Scintillation detector, for remote emergency situations Fig. 42: Scintillation detector, for remote emergency situations The appropriate action is sometimes difficult. The Table 9 below can be used as a guideline. The appropriate action is sometimes difficult. The Table 9 below can be used as a guideline.

Source of Suspected Advised type of Detector to use Counting Photon energy contamination radionuclides measurement time to search 50

Industries can be classified into three different parts: The Nuclear Sector (power plants, extraction and production of fuel, reprocessing plants, waste management plants). The non-nuclear sector (non-nuclear industries making use of ionizing radiation: radiology, nuclear medicine, radiotherapy and scientific research). The non-nuclear industry involves the non-nuclear installations working without nuclear products. It was discovered that these industries could be a source of irradiation and contamination of workers because of natural radioactive materials present in high concentrations (Naturally Occurring Radioactive Materials or NORM's are phosphates, the ferrous and non-ferrous minerals, glass, ceramic's,...). These NORM's can be sources of high doses and a high level of contamination. The concerned radionuclides are the families of 238U, 235U, 232Th and the products that can be found in the body are 222Rn, 210Po, 210Pb, 210Bi, 226Ra. The most important is probably thorium which is found in different industries.

EMERGENCY PREPAREDNESS AND INTERNAL CONTAMINATION MONITORING

An incident resulting in the contamination of a person or a group of the population always requires the ability to respond to the emergency. The preparedness for a singular contamination accident is similar from the point of view of the material but differs in the procedural aspect. When an accident occurs far from the laboratory, a portable measurement system as shown in Fig. 42 is required (detector, module with high voltage power supply, amplifier, MCA and a computer ).

Fig. 42: Scintillation detector, for remote emergency situations

The appropriate action is sometimes difficult. The Table 9 below can be used as a guideline.

51 Source of Suspected Advised type of Detector to use Counting Photon energy contamination radionuclides measurement time to search Reactor Fission products WBC, Lung NaI(Tl) 30 min (except iodines) measurement Reactor Activation WBC, Lung NaI(Tl) 30 min. 1.17,1.33 MeV products: 60Co measurement Reactor Iodine (131I) Thyroid NaI(Tl), HPGe 10 min 365 keV Particle 123I, 125I, 129I Thyroid low energy 10 min accelerator HPGe Reactor, Particle 99mTc Thyroid, WBC, low energy 10 min accelerator Specific organ HPGe Fuel extraction: 238U, 235U, 234U Lungs low energy 50 min. 63.3, 92.6, 185.7 Uranium (natural) HPGe keV Fuel enrichment: 235U Lungs low energy 50 min. 185.7 keV Enr. uranium HPGe Fuel enrichment: 238U Lungs low energy 50 min. 63.3 keV Depl. uranium HPGe 92.6 keV Fuel fabrication 239Pu Lungs low energy 50 min. 17. keV with recycling: Pu HPGe Fuel fabrication 241Am Lungs low energy 50 min. 59.6 keV with recycling: HPGe Particles of recycled fuel Radionuclide 238U, 235U, 234U, wound HPGe or 10 min. 17, 63.3, 92.6 or manipulation: 239Pu, 241Am NaI(Tl) with 185.7 keV Wound with collimation contamination device TableTable 9: Some 9: Some of ofthe the appropriate appropriate actions actions for for in-vivo in-vivo monitoring monitoring 271 in incase case of of contaminationcontamination accident accident

SELECTED NUCLIDES SELECTED NUCLIDES Potassium in the body

The body Potassium of an adult malein the has body about 140 g of natural potassium (isotopes 39K, 40K and 41K) . Only the isotope 40K (0.0117 % or 16 mg) is radioactive (T½ = 1.28 109 a) which leads to a total activity of 4230 The Bq bodyuniformly of andistributed adult male in the hasbody about (30.92 140 Bq( 40gK)/gK). of natural This radionuclidepotassium can decay(isotopes according 39toK, the 40 differentK and 41waysK) .shown Only inthe Fig. isotope 43. This 40 isotopeK (0.0117 is easily % ordetected 16 mg) by wholeis body radioactivecounting. A 8"x4" (T½ detector = 1.28 (R=0.4 109 a) %) which allows leads a precision to a totalof 5 % activity (1�) for ofa measurement 4230 Bq of two thousand seconds. uniformly distributed in the body (30.92 Bq(40K)/gK). This radionuclide can The decay potassium according burden to of the a persondifferent is not ways cons showntant even in inFig. the 43. absence This isotope of muscular is or metaboliceasily disease. detected by whole body counting. A 8”x4” detector (R=0.4 %) allows a precision of 5 % (1σ) for a measurement of two thousand seconds. 52 The potassium burden of a person is not constant even in the absence of muscular or metabolic disease.

Fig. 43: Decay modes of 40K (simplified sketch) 40 40K Fig.delivers 43: Decay a dose modes of ofabout K 0.2(simplified mSv/year sketch) to the gonads, the soft 272 40 Ktissues delivers and a dose about of about 0.15 0.2 mSv/a mSv/year to the to theskeleton. gonads, theThe soft biological tissues and half-life about 0.15 of mSv/a to thepotassium skeleton. Theis 30 biological days. half-life of potassium is 30 days.

Cesium-137

137Cs is a fission product of uranium and of plutonium. It is produced 1.6 times more abundantly than 90Sr. With a physical half-life of 30.2 years, it was widely spread into the air during the atmospheric nuclear weapon tests and after the accident in Chernobyl in April 1986. It has been fed into the ecological cycle and is measurable in the body of all people. It is one of the most common radionuclides produced by nuclear power plants. Its biological half-life has a first compartment of 2 days (10%) and a second one of 105 ± 5 days ( 90%). 137Cs concentrates in muscle. 137Cs, a β-emitter, is readily assessed by measuring the 662 keV emitted by its daughter 137Ba (half-life = 2.6 min). The burden of 137Cs has been followed in the general public to establish some ecological parameters in the food chain. 53

Cesium-137

137Cs is a fission product of uranium and of plutonium. It is produced 1.6 times more abundantly than 90Sr. With a physical half-life of 30.2 years, it was widely spread into the air during the atmospheric nuclear weapon tests and after the accident in Chernobyl in April 1986. It has been fed into the ecological cycle and is measurable in the body of all people. It is one of the most common radionuclides produced by nuclear power plants. Its biological half-life has a first compartment of 2 days (10%) and a second one of 105 � 5 days ( 90%). 137Cs concentrates in muscle. 137Cs, a �-emitter, is readily assessed by measuring the 662 keV emitted by its daughter 137Ba (half-life = 2.6 min). The burden of 137Cs has been followed in the general public to establish some ecological parameters in the food chain.

137 FigureFigure 44: 44: 137CsCs in in thethe body of of the the Belgian Belgian general general public public between between 1959 and 1959 1999. and 1999. 137 273 The graph in Fig. 44 presents the mean body burden of Cs for a sample (30 to 70 measurements)ofThe graph in Fig. the Belgian 44 presents general the pub licmean measured body since burden 1959 of at 137theCs SCK for�CEN. a sample The results are normalised to a standard man of 70-kg containing 140 g of K. The(30 secondto 70 measurements)of histogram of Fig. 44, the presen Belgianted ingeneral a logarithmic public scale,measured is the since �-activity 1959 of the air measuredat the SCK on the•CEN. site of The the resultslaboratory are of normalised the SCK�CEN to (monthlya standard means) man and of indicates70-kg a shift betweencontaining the activity 140 g in of the K. air and the 137Cs burden in the body. 137 TheThe first second peak of histogram 910 Bq of ofCs Fig. (responsible 44, presented of 36.  inSv/year a logarithmic to the whole scale, body) is appeared the β- in 1964, aboutactivity one yearof the after air the measured Limited Test on Ban the Trea sitety of (Moscow the laboratory August 5, of 1963). the SCKThe second•CEN peak (260 Bq, 10 Sv/year) occurs 13 months after the Chernobyl accident in April 1986. The sharp injection of(monthly137Cs into means) the atmosphere and indicates permits the a determinatshift betweenion of thean ecological activity half-lifein the air found and to be 12.6 137 monthsthe Csas shown burden in Fig.in the 45. body. 137TheCs first is easily peak eliminated of 910 Bq from of the137Cs body (responsible (through faeces) of 36. with µSv/year administration to the of whole Prussian Blue body) appeared in 1964, about one year after the Limited Test Ban Treaty (Moscow August 5, 1963). The second peak (260 Bq, 10 µSv/year) occurs 13 months after the Chernobyl accident in April 1986. The sharp injection of 137Cs into the atmosphere permits the determination of an ecological half-life found to be 12.6 months as shown in Fig. 45. 137Cs is easily eliminated from the body (through faeces) with administration

of Prussian Blue (Fe4[Fe(CN)6]3). This chemical has no secondary effects. 54

(Fe4[Fe(CN)6]3). This chemical has no secondary effects.

1000

100

10 for a standard man Cs-137 Burden (Bq)

1 0 20 40 60 80 100 Month (from Jan 1985 till Dec 99)

137 Fig. 45: Fig.137Cs 45: body burdenCs body in non-professionally burden in non-professionally occupied Belgian occupied populatio nBelgian populationbetween 1985 between and 1999. 1985 and 1999.

Strontium-90 Strontium-90and strontium-89 and strontium-89 90Sr (physical half-life = 28.78 a) is a pure �-emitter (546 keV) and is difficult to measure in 90 vivo274. 90Sr is a bone seekerSr and(physical deposits half-lifein sites iden =tical 28.78 to calcium a) is a (bones pure andβ-emitter teeth) with (546 a long keV) biological half-life.and is It difficultcan be assessed to measure with the in least vivo squares. 90Sr fitting is a boneapplied seeker to the whole and depositsspectrum in but is best measured with the indirect methods (urine and faeces) and the bone content is estimated sites identical90 to calcium (bones and teeth) 137with a long biological half- with metaboliclife. models. It can The be Srassessed body content with is the estimated least fromsquares the fittingCs body applied content. to It hasthe been whole shown that the ratio 90Sr/137Cs is different in diverse constituents of the food but remains constant in each constituent.spectrum Indirect but measurements is best measured (urine samples) with the allow indirect corroborating methods these(urine results. and faeces)It is 90 known that 90andSr and the 137 boneCs are contentproduced isin aestimated ratio of 1 to with 1.6 (value metabolic considered models. by UNSCEAR The Sr after body the Chernobylcontent accident is to estimated assess the fromfallout the of 90137Sr).Cs 90bodySr has content. been used It hasin huge been quantities shown sincethat the 1961 as a heatratio source 90Sr/ for137 thermoelectricCs is different generato in diversers in autonomous constituents remote of theweather food stations but remains and 90 90 ocean light buoys.constant An additional in each hazardconstituent. from Sr Indirect is due to measurements its daughter isotope (urine Y (half-life= samples) 64.2 allow hours): it exists in secular equilibrium with its parent and emits 2.27 MeV �-particles. corroborating these results. It is known that 90Sr and 137Cs are produced in THE RECENTa ratio DEVELOPMENTS of 1 to 1.6 (value OF IN considered VIVO MEASUREMENTS by UNSCEAR after the Chernobyl accident to assess the fallout of 90Sr). 90Sr has been used in huge quantities For several years, computerised tools designed for the collection, analysis and manipulation sinceof spectra 1961 have as beena heat used source for the for automation thermoelectric of direct measurementgenerators in techniques autonomous in Whole Body remote Counting. weather New detectors stations alsoand haveocean been light developed buoys. An for theadditional counting hazard itself and from especially the90 lowSr isenergy due semiconductorto its daughter detectors. isotope 90Y (half-life= 64.2 hours): it exists in secular equilibrium with its parent and emits 2.27 MeV -particles. Whole body counting with semiconductors detectors β

Recently, the HPGe detectors are being used in Whole Body Counting as replacement for THE RECENT DEVELOPMENTS OF IN VIVO MEASUREMENTS

For several years, computerised tools designed for the collection, analysis and manipulation of spectra have been used for the automation of direct measurement techniques in Whole Body Counting. New detectors also have been developed for the counting itself and especially the low energy semiconductor detectors.

Whole body counting with semiconductors detectors

Recently, the HPGe detectors are being used in Whole Body Counting as replacement for scintillation detectors. They are useful in special cases where the resolution of the scintillation detectors is not sufficient for the identification of the radionuclide.

The drawback of the HPGe detector is its low counting efficiency, which requires the use of several detectors working in an array. In routine 275 applications, when the detection limit can be high, a HPGe detector with a relative efficiency of 50 % is enough. Some research applications in the low energy region require specific shape and size of HPGe crystal to reduce the detection limits without changing the efficiency for the considered energies.

The HPGe detector can be used as a complement to scintillation measurement for the identification of radionuclides before an acquisition with a tailored NaI(Tl) detector. 55 scintillation detectors. They are useful in special cases where the resolution of the scintillation detectors is not sufficient for the identification of the radionuclide.

The drawback of the HPGe detector is its low counting efficiency, which requires the use of several detectors working in an array. In routine applications, when the detection limit can be high, a HPGe detector with a relative efficiency of 50 % is enough. Some research applications in the low energy region require specific shape and size of HPGe crystal to reduce the detection limits without changing the efficiency for the considered energies.

The HPGe detectorRoom can temperature be used as a complementdiodes to scintillation measurement for the identification of radionuclides before an acquisition with a tailored NaI(Tl) detector. The diodes work at room temperature and are more sensitive to Room temperaturelow energydiodes photons. These diodes can be placed in carefully shielded containers (Fig. 46) to eliminate the electronic noise . The advantage of the The diodes work at room temperature and are more sensitive to low energy photons. These diodes can besmall placed diodes in carefully is that shielded they contai can beners used (Fig. 46)in geometry’s to eliminate the particularly electronic noise adapted . The to advantage of the small body diodes (Fig. is 10.3) that they can be used in geometry's particularly adapted to the body (Fig. 10.3) The error due to a detector positioned too far from the source can be very The error due to a detector positioned too far from the source can be very important as mentioned by Kramer. The techniqueimportant of asroom mentioned temperature by diodes Kramer. array placed The techniquein contact with of the room body temperature(Fig. 10.3) leads to the improvementdiodes array of the placed accuracy. in contact with the body (Fig. 10.3) leads to the improvement of the accuracy.

276

Fig.Fig. 46: Silicon 46: Silicon diode arraydiode in arraya shielding in a box.shielding box. Commentaire [SCK8] : Thre Measurement of high levels of contamination e_didoes_color.bmp Commentaire [SCK9] : Large, very sensitive NaI(Tl) detectors in small counting rooms are not appropriate for Commentaire [SCK10] : Measurement of high levels of contamination

Large, very sensitive NaI(Tl) detectors in small counting rooms are not appropriate for counting of high levels of contamination: the count rate becomes so high that the dead-time of the acquisition system leads to a modified spectrum inappropriate for an accurate analysis. The only way to measure these cases is to work outside a shielded room. At SCK•CEN, a coaxial HPGe semiconductor detector with a low efficiency (10.6 % of relative efficiency) and the peak analysis method are used. The high resolution of the detector allows a good determination of the background and the person-detector distance can be adjusted to the level of contamination. This technique requires a model determining the efficiency of the detector under measurement conditions. This can be done by numerical methods. A computer programme (ATT3D) can calculate the absolute efficiency of a detector in special geometrical conditions using a point geometry efficiency, the mechanical characteristics of the detector and the description of the measurement conditions (distance and 277 orientation of the measured person or sample). The more complex code MCNP is of course appropriate but more difficult to use.

The in vivo measurement with gamma camera

For several years, different laboratories have used gamma cameras for the detection, quantification and localization of radionuclides in the body. These machines, used for metabolism studies, can be used as WBC facilities. INTERCOMPARISON AND INTERCALIBRATION

The calibration of the device is in itself a complex operation because the measurement accuracy should be estimated for each type of measurement (e.g. the discrepancy between the phantom and the measured persons). The distributions of the deposited radionuclides are also unknown. The morphologies of population in different countries indicate that the calibration must be made with “adapted” phantoms (e.g. Livermore and JAERI torso). For example, a person measured in facilities using each a different type of phantom would be assigned different values for the same burden. And both laboratories are considered to work with the same meticulousness. Attributing the different results to a different calibration phantom is correct but does not allow any comparison between the two laboratories, although it is asserted for a good metrology laboratory. There is also potential error due to external contamination. The problem of low energy photon emitters (< 100 keV) is another domain were systematic 278 error can occur if the results are not correctly interpreted. Intercalibration is another procedure by which a single standard is used to establish a common basis for measurements in different laboratories.

FROM COUNTING TO BURDEN TO DOSE: The question of the accuracy

The most difficult task in an WBC is the establishment of a error on the measurement. The more accurate assessment of the burden, the more precise estimation of the dose.

A common range of error in WBC is 100 % on the result of the burden. The most precise measurement is the counting of the thyroid or of a superficial wound where the estimation of the burden is 20%. But a counting of a lung contaminated with plutonium or with 241Am can lead to error of 800% on the burden assessment. Many efforts are furnished to reduce these errors (mainly with the aid of intercomparisons. But these procedures are not able to improve the accuracy of an actual measurement (reduce the systematic errors). Only the use of multi-detector arrays is able to solve partly the problem.

RULES TO FOLLOW DURING THE CHOICE OF MATERIALS IN THE DESIGN OF AN IN VIVO COUNTING FACILITY

There are two points that must be considered carefully and both concern the background. In an in vivo counting facility, the final goal is to determine the body burden of selected radionuclides with low enough detection limits. The detection limits are related to the background level and especially to the continuum found in the room and introduced in the room (detectors, electronics, mechanical support devices and the measured person). All these devices are made of steel, aluminium, beryllium, glass,.... Steel can be contaminated with 60Co; glass also contains 40K, aluminium and 279 beryllium also are contaminated with different natural radionuclides.

There are two ways to improve a measurement:

1. Select the good materials for the building of the different components. The steel must be selected as free of 60Co. The lead should be as old as possible. A beryllium window used in low energy photon detectors can be replaced by carbon epoxy if the measured energies are higher than 10 keV. Sometime, it is better to make the measurement out of a shielded room when low energy photons are examined.

2. Match the detector size to the investigated photon energy: most of the time, a detector is chosen for a defined application (measurement of plutonium, uranium, thorium,...). A different detector should be selected if the best detection limits are required. TREATMENT OF INTERNAL CONTAMINATION

The treatment after an internal contamination is based on two aspects: Reduce the absorption and stimulate the excretion.

The chronology observed in case of contamination and treatment is often the same:

Suspicion of contamination occurs after an alarm or other unusual • 60 event, TREATMENT OF INTERNAL CONTAMINATION • Counting is performed (organ, wound or whole body counting), The treatment• The afterradionuclide an internal contaminationis identified isand based quantified, on two aspects: Reduce the absorption and stimulate• Pre-treatment the excretion. is applied: washing, flushing, cleaning. The chronology• If necessary, observed the in caseadministration of contamination of chemicals and treatment for is chelation. often the same:

Administration� Suspicion of of contamination chemicals is occurs based af ter on an two alarm points: or other theunusual reduction event, of 280 � Counting is performed (organ, wound or whole body counting), intestinal� The absorption radionuclide and is identifiedthe stimulation and quantified, of excretion. These actions are induced� Pre-treatmentby using different is applied: kinds washing, of chemicals flushing, cleaning. according to the metabolic properties� If necessary, of the contaminant. the administration Several of chemicals of these for chelation. chemicals are given in

TableAdministration 10. of chemicals is based on two points: the reduction of intestinal absorption and the stimulation of excretion. These actions are induced by using different kinds of chemicals according to the metabolic properties of the contaminant. Several of these chemicals are given in Table 10.

Nuclides Reduction of Stimulation internal absorption of excretion

60Co Co salts DTPA, Co-EDTA 137Cs, 204Tl Prussian blue Prussian blue 228Th Adsorbents DTPA, EDTA Uranium Adsorbents Bicarbonate 65Zn Adsorbents Zn-DTPA, EDTA 95Zr Adsorbents DTPA, EDTA 239, ...Pu Adsorbents, anti-acids DTPA, EDTA, Calixarenes 123,125,131I Iodide Iodide, perchlorate

Table 10: Chemicals used for reducing absorption and stimulation excretion of radionuclides deposited in vivo. PERSPECTIVES AND CONCLUSIONS

The quantitative γ-ray spectrometry techniques are not the same for radionuclides in the body or for radionuclides in samples: the human body is of large mass and variable in size, shape and composition. The distribution of the radionuclides in the body is not uniform, unknown and variable with time after intake. These factors lead to complications with calibration. The duration of measurement is usually a limiting factor, and this leads to difficulties with achieving the required detection limits. The human body also contains radionuclides (natural 40K and, possibly, other radionuclides that are widespread in the environment). These photon emitters may interfere with detection of the radionuclides of interest and modify the detection limits.

The in vivo assessment of radioactive burdens by direct methods present several advantages: prompt results, possibility to localise the burden 281 and to measure specific organs; all photon emitters can be quantified simultaneously. Sensitivity (ability to detect certain radionuclides with low detection limits) is very good for most of the photon emitters. Disadvantages also exist for direct methods: detection limits are not low enough for certain radionuclides. It is sometimes possible to confuse internal and external contamination. Direct measurement techniques are not competitive with indirect techniques, they are complementary in the common goal of determining a committed dose.

Work is still required to improve the accuracy of the results and reduce the limits of detection. Both aspects can be improved with new detector technologies.

Techniques have considerably changed in fifty years in the measurement of body burden by the direct methods. The purposes also are changing: the present goals are more oriented to improved accuracy and the techniques are used for research.

Another important goal is the reduction of the detection limits. The solution to achieve this goal is the design of detector with shapes and sizes optimised for the photon energy. That means that there could be less multitask detectors and the number of detectors in a laboratory could increase in the future.

This text wanted to give an overview of the techniques that have been developed in the field of the whole body counting. The description is mainly based on the experience acquired in the laboratory of in vivo measurement of the SCK•CEN. In spite of its long history, some progress has been made in the last few years in the automation and the use of new detectors. Finally the most important aspect to mention is the use of the computer for detailed analysis of results and for automation of routine procedures. The use of in 282 vivo counting has gone beyond the domain of the nuclear energy production; the improvement of its techniques is due to the interaction between these different sciences, has lead to a better understanding of metabolism and kinetic models and has brought improvements in the protection of workers and in the treatment of contamination with radioactive materials. BIBLIOGRAPHY

B. ALTSHULER B. AND B. PASTERNAK Statistical Measures of the Lower Limit of Detection of a Radioactivity Counter. Health Phys., Vol. 9 - 1963.

ANBAR M., GUTTMANN S., RODAN G.A., STEIN J.A. Dynamic Study of thyroxine Deiodination in Humans – Research Laboratories Annual Report (period Jan.-Dec. 1965).

BEAN A., BIAN Z., DOBBINS J., JIM K., KADASWANY J., MISTRY N. – On The Stability of Low-Leakage Silicon Photodiodes Used With Crystal Calorimeter. Nucl. Instr. & Meth. In Physics Research, Vol. 33, N° 1, Feb. 1986.

BIAN Z., DOBBINS J., MISTRY N. – The Use of Silicon Photodiode in a CsI Calorimeter. Nucl. Instr. & Meth. in Physics Research, Vol.A239, 283 Sept 1985.

G. BLANAR, H. DIETL, J.DOBBINS, G. EIGEN, E. LORENZ, E. PAUSS, W. PIMPL, H. VOGEL and P. WEISSBACH Photodiode Readout for Scintillation crystals of BGO and NaI(Tl), Nucl. Instr. & Meth. in Physics Research, Vol.203, pp.213-221 - North Holland Publishing Company – (1982).

BURGER P. Industrial Applications of Passivated Ion Implanted Silicon Detector. Nucl. Instr. & Meth. in Physics Research, Vol.226, pp 45-49 (1984).

BURGER P. Manufacturing, Performance and New Development s in Silicon Counters in High Energy Physics. Nucl. Instr. & Meth. in Physics Research, Vol.226, pp 112-116 (1984). BROWNE E. & FIRESTONE R.B. - Table of Radioactive Isotopes. John Wiley and sons - 1986.

BUSH M., Energy Absorption in Radium Therapy –F. Brit. J. Radiol. 19: 14-21. 1946.

CLAXTON K.T. Principles and Techniques of Gamma-Ray Tracers. AERE Harwell ISBN O-70-580287-6. (1976).

R.H.CLARKE - 1990 Recommandations of ICRP. National Radiological Protection Board - 1991.

J.F. COLARD, D. NUTTINCK - Détection du 239Pu dans les blessures. (C.E.N./S.C.K) 1965.

COLARD J.F., LEDUC R.E. Assessment of Radioactive Burdens in 284 Human Body by Direct Methods. C.E.N./S.C.K., Mol April 1980.

COLARD J. Incorporation de 133Xe; Mesure directe, aperçu de l’expérience au CEN et des données de la littérarure. O.A.-CEN – RB/JC/yw S/N80- 174 (1980).

COLARD J.F., CULOT J.P., DI FERRANTE E. Observation de quelques cas de contamination interne par du 75Se, du 175Hf et du Th naturel. Assessment of Radioactive Contamination in Man 1984. Symposium, Paris 19- 23 nov 1984, organized by IAEA in co-operation with WHO. IAEA-SM-276/37, pp 421-432.

P.N. COOPER Introduction to Nuclear Radiation Detectors. Cambridge University Press - 1986.

CROSS W.G., ING H. (1985) Sodium Activation in the Human Body. Radiat. Prot. Dosimetry Vol. 10 No 1-4, 266. L. A. CURRIE Limits for Quantitative Detection and Quantitative Determination.Application to Radiochemistry. Anal. Chem. 40, 586, 1968.

DAVITI M., PARASKEVOPOULOS K.M., ANAGNOSTOPLOULOS A., POLYCHRONIADIS E.K. – Growth, Optical and Electrical

Characterization of HgBr1.13I0.84. - Nucl. Instr. & Meth. in Physics Research, Vol. A380 (1996) pp 62-65.

DECLERCQ C. Direct Meting van Th-Longbesmetting met Ge-Detectoren. SCK•CEN – Hoge School Limburg. 1999.

DELWAIDE P., VERLY W., COLARD J. Détermination du potassium total chez l’homme. R2007 - CEN/SCK. May 1961.

DELWAIDE P. A 4 π plastifluor Body Counter for Clinical Use. Intern. J. 285 Appl. Radiat. Isotopes. 20 pp. 823-639. (1969).

DELWAIDE P. Etude, par anthropogammamétrie, du potassium corporel humain dans des condition normales et pathologiques. Service de Chimie médicale et de Toxicologie. Faculté de Médecine - Université de Liège. 1976.

DIAMOND G.L. Biological Consequences of Exposure to Soluble Forms of Natural Uranium. Radiat. Prot. Dosim. Vol. 26 pp. 23-33 (1989).

DZUBAY Thomas G. X-ray Fluorescence Analysis Of Environmental Samples. U.S. Environmental Protection Agency - Ann Arbor Science Publishers Inc (1977).

EGGERMONT G. Kr-85 Proceedings of a workshop in SCK•CEN Brussels, October 1998. BLG-835, Mol. (1999). EISENMENGER A., TSCHAMMER A., RIEDEL W. Monitoring of thorium incorporation by thoron in breath measurement: Methodology, Improvements and Determination of burden in Workers. May 25 – 25, 1999 Mol, Belgium. Radiat. Prot. Dosim. Vol. 89, Nos 3-4, pp. 203- 206 (2000).

F. d’ERRICO, A. J. J. BOS Passive detectors for neutron personal dosimetry: state of the art. RadiaT. Prot. Dosim. Vol. 110(1-4) pp. 195-200 (2004).

EISENBUD M. Environmental Radioactivity. From Natural, Industrial and Military Sources . ACADEMIC PRSS, INC. – (1987).

ENTINE G. – Applications of Cde to Nuclear Medicine. DOE/EV/ 02541- T2.DE85 011877. 286 FRANCIS J. Surface -polishing process for NaI crystals. Stanford Linear Accelerator Center – (September 1982).

FRIANT A. Perspectives Offertes Par Les Détecteurs HgI2 en MicroAnalyse. CEA, CN Saclay, IRDI, DEIN. Meeting of Microprobe and Scanning Microscope. ANRT group. Issy-les-Moilineaux (France) 15- 16 mai 1984.

D. FRANCK, N. BORISSOV, L. DE CARLAN, N. PIERRAT, J. L. GENICOT AND G. ETHERINGTON Application of Monte Carlo calculations to calibration of anthropomorphic phantoms used for activity assessment of actinides in lungs. Rad. Prot. Dosim. 105:403-408 (2003)

A. GAVRON GLDT- An improved fortran IV computer program for the least squares analyses of gamma ray spectra. Israël Atomic Energy Comission. (1969). GENICOT J.L. Utilisation des détecteurs à semiconducteur dans les mesures de la contamination interne par anthropogammamétrie. Lic. I.S.N.A.P. - U.C.L. (1988).

GENICOT JL, ALZETTA JP, VANMARCKE H. Automatic Acquisition and Management System for NaI(Tl) Spectra. BLG-636 CEN•SCK (1992).

GENICOT J.L. The Measurement of incorporated radioactive actinides in the body by direct methods. Journal of Alloys & Compounds, 213/214 (1994) pp 484-485.

GENICOT J.L., HARDEMAN F. A measurement of the Ecological Half Life of 137Cs in Belgium. Health Phys. Dec 1994, pp 669-670 (1994).

GENICOT J.L., HARDEMAN F., OBERSTEDT S. The Assessment of Plutonium and Americium in Contaminated Wounds with High Energy 287 Resolution Semiconductor Detectors. Appl. Radiat. Isot. Vol 46, N°3, pp.199-203. (1995).

GENICOT J.L., The Measurement of Radioactive Body Burdens by the Direct methods at the CEN•SCK. BLG-642 (1995).

GENICOT J.L., HARDEMAN F., WAETERMANS F. Deterministic Analytical Method for the Calibration of Semiconductor Detectors in Gamma Ray Spectrometry. Advances in Radiation Measurements. Applications and Research Needs in Health Physics and Dosimetry. 3-6 October 1994, Chalk River, Ontario, Canada. Radiat. Prot. Dosim. Vol.61, No. 1-3, pp141-144. (1995).

GENICOT J.L. Les mesures de contamination pulmonaire en actinides par la méthode directe; Nouvelles techniques Annales de l’Association belge de Radioprotection 20:4, 261-288 (1995). GENICOT J.L., CULOT J.P., HARDEMAN F., ALZETTA J.P., VANMARCKE H.. The Measurement of Am-241 in the body with a double low energy germanium detector system. I.R.P.A 9 Vienna, Austria - April 14-19, 1996.

GENICOT J.-L., ALZETTA J.P. New technique using room temperature diodes for the direct assessment of internal contamination by low energy gamma-ray emitters. Appl. Rad. & Isot. - Vol. 48, No. 3, pp. 349-358. March 1997.

GENICOT J.-L. Room Temperature Semiconductor Detectors for in- vivo Monitoring of Internal Contamination. International Conference on Radiation and health.Beer Sheva, Israel, November 3- 7, 1996. Environmental Health Perspective. Vol 105, Suplement 6; 1423-1426. (Dec. 1997).

288 GENICOT J.L., POMMÉ S., Attenuation Calculation of Low Energy Photons: Application to In-Vivo Spectrometry Using Multi-Diode Systems. Radiation Protection Dosimetry. Vol. 81, No. 2, pp.113-122. Feb. 1999.

GENICOT J.L., POMMÉ S., ALZETTA J.P. In Vivo Measurement of Low Energy PhotonEmitters: Room Temperature Semiconductor Diodes Versus Large Scintillators and Germanium Crystals. Health Phys. 76 (3), pp 288- 299. (Mar.1999).

GENICOT J.L. Anthroporadiametry of Low Energy X- and Gamma Photons: Development of a New Technique Based on Room-Temperature Semiconductor Detectors. Thesis Univ. Cath. de Louvain (Mars 1999).

GENICOT J.L. L ’Anthroporadiamétrie: Une technique évolutive pour répondre aux directives de la CIPR. Lecture presented to the Belgian Association of Radiation Protection (ABR-BVS) o, Feb. 25, 2000. Published in the Annales de l’Association Belge de Radioprotection- Annalen van de Belgische Vereniging voor Stralings-bescherming. Vol. 25, N° 2, 2000.

GENICOT J.L. The In Vivo Detection of Low Energy Photon emitters in Radiation Protection and in Nuclear Medicine: a New philosophy for new needs in In VivoCounting. InVivo Monitoring of Internal Contamination: New Techniques for New Needs. International Workshop. May 25 – 25, 1999 Mol, Belgium. Radiat. Prot. Dosim. Vol. 89, Nos 3-4, pp 339-342 (2000).

GENICOT JL, GEBOERS I., DAMEN A., FRANCK D., DE CARLAN L., “The Reduction Of Limits Of Detection In In Vivocounting Of Low Energy Photon Emitters by Optimizing The Shape And Size Of Detectors.” Internal Dosimetry Of Radio-Nuclides. Radiat. Prot. Dosim. VOL. 105, NO. 1-4, pp. 457-462 (2003).

GILMORE G., HEMINGWAY J., Practical Gamma-Ray Spectrometry. John Wiley & Sons (1995). 289

P.H. GOODA Evolution of Silicon photodiodes for detection of ionising radiation. Departement of Physics, University of Surey - Jan. (1988).

H. GRASSMANN, E. LORENZ and H.G. MOSER Properties of CsI(Tl) - Renaissance of an old scintillation Material Nuclear Instrument and Methods in Physics Research, Vol.228, pp.323-326. North Holland Publishing Company – (1985).

H. GRASSMANN and H.G. MOSER Improvements in photodiode Readout for Small CsI(Tl) crystals. Nucl. Instr. & Meth. in Physics Research, Vol. A253, pp.122-124. North Holland Publishing Company (1985).

GRIFFITH R. V. The role of Intercomparison and Intercalibrations in the Improvement of Internal Dose Assessment. In Vivo99. In Vivo Monitoring of Internal Contamination: New Techniques for New Needs. International Workshop. May 25 – 25, 1999 Mol, Belgium. Radiat. Prot. Dosim. Vol. 89, Nos 3-4, pp. 163-172 (2000).

GUILLAUME M.Production en Routine par cyclotron de Fluor-18 et Potassium-43 à usage médical au moyen d’une Cicble Gazeuse Télécommandée. Nucl. Instrum. Methods 136 pp. 185-195 (1976).

GUILMETTE R.A., LAURER G.R., HOOVER M.D., SNIPES M.B., Customising the LRRI In Vivo Bioassay Facility for Measuring 210Pb as a Biomarker for Exposure to Radon Progeny. In Vivo99. In Vivo Monitoring of Internal Contamination: New Techniques for New Needs. International Workshop.May 25 – 25, 1999 Mol, Belgium. Radiat. Prot. Dosim. Vol. 89, Nos 3-4, pp. 333-338 (2000).

G. DE HAAS, W.P.VERDEGAAL, C.N. de GRAAF, F.A. GARITSEN. BOHN, SCHELTEMA & HOLKEMA. Nucleaire Geneeskunde. Utrecht/ 290 Antwerpen (1984).

Hamamatsu Silicon Photodiodes and Charge Sensitive Amplifiers for Scintillation Counting and High Energy Physics – Cat. N° KOTH0002E01. Oct. 92 T.

HEINRICH W., Roesler S., Schrube H. Physics of Cosmic Radiation Fields. Radiat. Prot. Dosim. Vol. 86 No. 4, pp. 253-258 (1999).

L. HOLMSTOCK Thorium and Nuclear Power. Aspects about the Metabolic Behaviour of Thorium. K.U.L., Faculteit Geneeskunde - Leuven – (1985).

HUNT J.G., MALATOVA I., FOLTANOVA S., DANTAS B.M. Calibration of in vivo Measurement System Using a Voxel Phantom and the Monte Carlo Technique. In Vivo99. In Vivo Monitoring of Internal Contamination: New Techniques for New Needs. International Workshop. May 25 – 25, 1999 Mol, Belgium. Radiat. Prot. Dosim. Vol. 89, Nos 3-4, pp. 283-286 (2000).

IAEA Safety Practices – Direct Methods for Measuring Radionuclides in the Human Body. International Atomic Energy Agency, Vienna (Austria) STI/PUB—993. Safety Series. Safety practices. no. 114 (1996).

Recommendations of the International Commission on Radiological Protection. ICRP PUBLICATION 26 - Pergamon Press – (1977).

Recommendations of the International Commission on Radiological Protection. ICRP PUBLICATION 60 - Pergamon Press (1990).

Direct Determination of the Body Content of Radionuclides. ICRU Report 69. Journal of the ICRU) – Volume 3 No1 2003 – ISSN 1473- 6691 (2003). 291 ISHIGURE N., ENOMOTO H., NAKANO T., INABA J. Validity of 241Am as trecer of inhaled Pu in External Chest Counting. Intakes of Radionuclides – Occupational and Public Exposure. Proceedings of a Workshop , Avignon, France – September 15-18, 1997. Radiat. Prot. Dosim. Vol. 79, Nos 1-4, pp.133-136 (1998).

ISAKSSON M., ALPSTEN M., CEDERBLAD A., PETTERSSON N. In Vivo Identification and Localisation of Radioactive Contamination in the Human Body. In Vivo99. In Vivo Monitoring of Internal Contamination: New Techniques for New Needs. International Workshop. May 25 – 25, 1999 Mol, Belgium. Radiat. Prot. Dosim. Vol. 89, Nos 3-4, pp. 349-352 (2000).

IWANCZYK J.S. – Advances in mercuric Iodide X-Ray Detectors and Low Noise Preamplification Systems. Nucl. Instr. & Meth. in Physics Research, Vol. A283 (1989) pp 208-214. JANSSENS H. Radiologische Problemen met Natuurlijke Radioactiviteit in de Niet-Nuclaire Industrie. Paper presented to the “Belgische Vereniging voor Stralingsbescherming – Association Belge de Radioprotection. Sept. 25, 1998.

JEANGUILLAUME C., BÉGOT S., QUARTUCCIO M., DOUIRI A., BALLONGUE P. From Whole Body Counting to Imaging: The Computer Aided Collimation Gamma Camera Project (CACAO). In Vivo99. In Vivo Monitoring of Internal Contamination: New Techniques for New Needs. International Workshop. May 25 – 25, 1999 Mol, Belgium. Radiat. Prot. Dosim. Vol. 89, Nos 3-4, pp. 349-352 (2000).

JESKO T., ZVONOVA I., BALONOV M., THORNBERG C., MATTSSON S., WALLSTROM E., VESANEN R., ALPSTEN M. Age Dependent Dynamics of Ceasium Radionuclide Content in Inhabitants of the Bryansk Region, Russia; A Seven Year Study. In Vivo99. In Vivo Monitoring of 292 Internal Contamination: New Techniques for New Needs. International Workshop. May 25 – 25, 1999 Mol, Belgium. Radiat. Prot. Dosim. Vol. 89, Nos 3-4, pp. 179-182 (2000).

MCKEE B.T.A., GOETZ T., HAZLETT T., FORKERT L. – Performance of a 6 mm thick CdTe det. for 166 keV γ-rays. Nucl. Instr. & Meth. in Physics Research, Vol. A272 (1998) pp 825-833.

KIREEV P. La Physique des Semiconducteurs – Editions MIR - Moscou 1975.

G.F. KNOLL Radiation detection and measurement - Second edition. John Wiley & Sons. 1989.

KOVTUN A.N., PUZIKOV A.G., SOKOLOV I.A., KOZHEUROV V.P., DEGTEVA M.O. Anthropomorphic Phantom with Sr-90 Incorporated in the Skeleton. In Vivo99. In Vivo Monitoring of Internal Contamination: New Techniques for New Needs. International Workshop. May 25 – 25, 1999 Mol, Belgium. Radiat. Prot. Dosim. Vol. 89, Nos 3-4, pp. 301-304 (2000).

KRUCHTEN D. A. Rib Effects in Lung Counting. 39th Annual Conference on Bioassay, Analytical and Environmental Radiochemistry. Colorado Springs, Colorado - Oct 11-15, 1993. Kramer G. Considerations in Assigned Dose based on in-vivo Counting. Int. Conf. on Radiation and Health. Beer Sheva, Israël, Nov. 3-7, 1996.

KRAMER G. Investigating the Impossible. In Vivo99. In Vivo Monitoring of Internal Contamination: New Techniques for New Needs. International Workshop. May 25 – 25, 1999 Mol, Belgium. Radiat. Prot. Dosim. Vol. 89, Nos 3-4, pp. 259-262 (2000).

KRAMER, GARY H., LEE, TAE-YOUNG, CHANG, SI-YOUNG. Chest Wall Thickness Measurements Of The LLNL Phantom For Small Area 293 Germanium Detector Counting. Health Physics. 79(2):203-206, August 2000.

MILLER C.E.; MARINELLI L.D. Radium Toxicity - ANL4531 (1950)

NCRP Report No 44 Krypton –85 in the atmosphere (1975).

NUCLEAR DATA SHEETS Vol. 53, (1988).

NESTOR O.H. and HUANG C.Y. Bismuth Germanate: A high-Z gamma- ray charged particle detector. I.E.E.E. Transactions ao Nuclear Science, Vol.NS-22, pp. 68-71 – (February 1975).

NEWTON D. TAYLOR B.T. EAKINS J.D. Difference clearance of Plutonium and Americium Oxides From the Human Lungs. Health Phys. Vol. 44 Siuppl. N°1, pp 431-439; (1983). NUTTINCK D., COLARD J.F., LEDUC R.E. Compteurs proportionnels pour la detection du 239Pu et des autres émetteurs α-X fixés dans les poumons. RB/JC/DN/yw - S/N73-153 (1973).

SPITZ HB, BUSHBOM RL, RIEKSTS GAA, PALMER HE. A New Method for Analysing High-Resolution Spectra from Whole Body Counter in-Vivo Measurements. Health Phys. Vol. 49, Nr 6, pp.1085-1096 (1985).

STRÜDER L. – Silicon Detectors for High Resolution Photon and Particle Detection. Advances in Radiat. Meas. Applications and Research Needs in Health Physics and Dosimetry. Int. Workshop OcT 3-6, 1994. Chalk River, Ontario (Canada).

PALMER H.E., BRIM C.P., RIEKSTS G.A., RHOADS M.C. Handford Whole Body Counting Manuel Operated for the U.S.-Departement of 294 Energy – (May 1987).

PAHUJA D.N. SONAWANE V.R., JAGTAB V.S, SAMUEL AM. Proceedings of the International Conference on Radiation Protection Measurements and Dosimetry: Current Practice and Future Trends (IARP- IC. 2K1). Anushaktinagar, Mumbai-400 094, India – Bulletin of Radiation Protection. (pp13-15). Jan. – June 2001.

PELLERIN P. MORONI J.P. REMY M.L. Premiers Résultats d’une Etude Systématique des Contaminations Internes Consécutives aux Retombées Radioactives. I.A.E.A. Heidelberg 11-15 may (1964). PANKOVE J.I. Optical Processes in Semiconductors. Prentice Hill, Inc. Englewood Cliffs, New Jersey – 1971.

POMROY C, MEASURES M. External gamma counting and bioassay measurements for 210Pb on retired uranium miners. J. Health Phys. 37 PP 409-412 (1979). POMMÉ S., UYTTENHOVE J., VAN WAEYENBERGE B., GENICOT J.L., CULOT J.P., HARDEMAN F. Radiocesium contamination in Belgium Journal of Radioanalytical and Nuclear Chemistry. Vol. 235, Nos 1-2, pp. 139-144 (1998).

QUARTUCCIO M., FRANCK D., PIHET P., BÉGOT S., JEANGUILLAUME C. Computer Assisted Collimation Gamma Camera: A New Approach To Imaging Contaminated Tissues. In Vivo99. In Vivo Monitoring of Internal Contamination: New Techniques for New Needs. International Workshop. May 25 – 25, 1999 Mol, Belgium. Radiat. Prot. Dosim. Vol. 89, Nos 3-4, pp. 343-348 (2000).

RAHOLA T., Falk R. Whole Body Measurement and Quality Assurance. In Vivo99. In Vivo Monitoring of Internal Contamination: New Techniques for New Needs. International Workshop. May 25 – 25, 1999 Mol, Belgium. Radiat. Prot. Dosim. Vol. 89, Nos 3-4, pp. 243-245 (2000). 295 REMENCHIK A. P., MILLER Ch. E., KESSLER W.V. Estimate of Body composition derived from Potassium Measurements. Body Composition in Animals and Man - Proceedings of a symposium held May 4,5 & 6, 1967. University of Missouri, Columbia, pp 231-260; pp 291-316.

ROTH M. – Advantages and limitations of Cadmium Telluride Romm Temperature Gamma-Ray Detectors. Nucl. Instrum. and Meth. in Physics Research, Vol.A283 (1989), pp.291-298.

RONNEAU Cl. Environmental Sources of Radioactivity. First Summer School on Radioecology. SCK•CEN Mol, Belgium. (8-20 July, 1990).

SHAWKI IBRAHIM. Is 238Pu more mobile in the environment than 239Pu? 39th Annual Conference on Bioassay, Analytical and Environmental Radiochemistry. Colorado Spring, Oct. 11-15, 1993. SOUZA J.F., DANTAS B.M., BRAGA F.J.H.N., BERTELLI L., GHILARDI NETTO T. In vivo Determination of incorporated activity of 99mTc-MDP in Bone Tissue. In Vivo99. In Vivo99: In Vivo Monitoring of Internal Contamination: New Techniques for New Needs. International Workshop. May 25 – 25, 1999 Mol, Belgium. Radiat. Prot. Dosim. Vol. 89, Nos 3-4, pp. 179-182 (2000).

SONAWANE V.R., JAGTAB V.S, PAHUJA D.N., SAMUEL AM. Evaluation of a dietary substance for its effect on the clearance of radio-cesium from in-vivo system in the rats (pp10-11). Proceedings of the International Conference on Radiation Protection Measurements and Dosimetry: Current Practice and Future Trends (IARP-IC. 2K1). Anushaktinagar, Mumbai- 400 094, India – Bulletin of Radiation Protection (2001).

SPITZ H.B., LODWICK J. Design, Fabrication & Evaluation of a 296 New Calibration Phantom for In-vivo Measurement of Bone-seeking Radionuclides Radiat. Prot. Dosim. 89(3-4), pp 275-282 (2000).

SQUILLANTE M.R., REIFF G., ENTINE G. – Recent Advances in Large Area Avalanche Photodiodes. IEEE Transactions on Nuclear Science. Vol. NS-32, n°1, Feb. 1985.

STANNARD J.N. Some historical highlights and portents for the future of biomedical research on radium and the actinides. Health Physics Vol.44, Suppl. no 1, pp 3-13. 1983.

SUMMERLING T.J., QUANT S.P. Measurements,of the human anterior chest wall by ultrasound and estimates of chest wall thickness for use in determination of transuranis nuclides in the lung. Rad. Prot. Dos. Vol. 3, N°4 pp. 203-210. 1982. SUZUKI Y., FUKADA Y., NAGASHIMA Y. – An Indium Phosphide Solid Dtate Detector. Nucl. Instrum. and Meth. in Physics Research, Vol.A275, pp. 142-148 (1989).

SURENDRAN T. HARIDASAN T.K. SHARMA R.C. KRISHNAMONY S. Experience at Trombay in Monitoring Actinides Intakes by occupational workers by direct external Counting. Radiation Protection Dosimetry. Vol. 59, N° 1, pp. 15-24 (1995).

SWINTH K.L., BAIR W.J., DEAN P.N., RUNDO G. and TOMLINSON F.K. Status and Trends in the external counting of inhaled heavy elements deposited in vivo. Helth Physics Vol. 37, pp641-657 - Nov 1986.

UNSCEAR 1993 - Sources and effects of Ionizing radiation. United Nation Scientific Committee on the Effect of Atomic Radiation. Report to the General Assembly, with Scientific Annexes 297 H. VANMARCKE De bijdrage van het woonmilieu tot de blootstelling aan straling afkomstig van nucliden uit de natuurlijke 238U reeks. Rijksuniversiteit Gent - Faculteit der Wetenschappen - Laboratorium voor Kernfysika. 1986-1987.

VANMARCKE H., GENICOT J.L. L’Evolution Du Déséquilibre Dans La Série Ru 232Th Suite à Des Différentes Hypothèses De Départ. Report SCK•CEN (1992).

J.VERDEBOUT. The Recent Developments in the Technology of Scintillator Detectors for Gamma-Ray Spectroscopy. Nuclear Science and Technology Comm. of the European Communities - 1988.

WAMBERSIE A. Endovascular Brachytherapy, Rationale, State of the Art, Radiobioligocal Issues, Survey of the Situation in Belgium. Workshop Cardiovascular Brachytherapy. Mol, Belgium, September 9, 2000. Clinical Experience with Intracoronary Irradiation. Workshop Cardiovascular Brachytherapy. Mol, Belgium, September 9, 2000.

WINTERBERG R.E., PIERCE J.F. – A Charge Sensitive Pulse Preamplifier with a Field-Effect Transistor Input Stage. DOE/OR/21400 (1963).

YAGAMATA N, YAGAMATA T. The concentration of cesium-137 in human tissues and organs.Nat. Institute Public Health (Jajan) 9,72 (1960).

YAMAMOTO H., HATAKEYAMA S. – Low-Energy Nuclear Radiation Detection With A Silicon Photodiode. Nucl. Instrum. and Meth. in Physics Research, Vol. A281 (1989), pp.128-132.

298 K. YAMAMOTO, Y. FUJII, Y. KOTOOKA and T. KATAYAMA Highly stable silicon PIN photodiode. Nucl. Instrum. and Meth. in Physics Research, Vol.A253, pp.542-547 - North Holland Publishing Company - 1987

YOUNG D.R., FOLSOM, T.R. Cesium accumulation in muscle tissue of marine fishes. Health Physics. Vol 37 pp 703-706. Pergamon Press – (1979).