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Rolf Maximilian Sievert (1896-1966) V. simpozij HDZZ, Stubičke Toplice, 2 HR0300030 ROLF MAXIMILIAN SIEVERT (1896-1966) Ivan Tomljenović Prirodnomatematički fakultet Banja Luka, M Stojanovića 2, Banja Luka, Bosna i Hercegovina e-mail: [email protected] UVOD CGPM (Conference General de Poids et Mesures), odnosno Generalna konferencija za utege i mjere, na svom XVI-tom zasjedanju 1979. god. donijela je odluku da se jedinica za ekvivalentnu dozu nazove sivert, oznaka Sv, u čast švedskog fizičara Rolf Maximilian Siverta. Ta jedinica je dio SI jedinica. Ideja članka je da se metrolozi i dozimetristi upoznaju sa životom i radom ovog zaslužnog naučnog radnika u oblasti radiološke zaštite. DEFINICA JEDINICE Prema ICRU (International Commission on Radiation Units and Measurements) i ICRP (International Commission on Radiological Protection) ekvivalentna doza (H) je produkt apsorbirane doze (D) i faktora modifikacije (Q, DF, N). N = Q'N'D = Q'D (1) gdje je: Q (quality factor) faktor kvaliteta, čija je vrijednost određena za svaku pojedinu vrstu zračenja, DF (distribution factor) faktor distribucije, N geometrijski faktor koji se uzima da je jednak jedinici. Pošto su faktori modifikacije bezdimenzioni, onda se i ekvivalentna doza izražava u jedinicama kao i apsorbirana doza, J/kg. Jedinici je dato ime sivert, Sv. l Sv = l J/kg (T) Jedinica pripada međunarodnom sustavu jedinica (SI). Ranije se koristila jedinica rem, roentgen equivalent man, (rentgen ekvivalentan čovjeku). Veza stare i nove jedinice je: l Sv = 100 rem (3) Ovom jedinicom se mjere također i kolektivna ekvivalentna doza SK, uslovna doza Hc, vezana ekvivalentna doza HSO i efektivna doza E. 49 V. simpozij HDZZ, Stubičke Toplice, 2003 STRUČNI ŽIVOTOPIS Švedski naučnik, zdravstveni fizičar Rolf Maximilian Sievert rođen je 6. maja 1896. (u nekim dokumentima 1898.) u Stockholmu (Švedska). Njegov djed je emigrirao iz Njemačke u Švedsku gdje je postao uspješan fabrikant. Nakon očeve smrti Rolf Sievert je trebao da preuzme vođenje očeve firme. Međutim, vrlo brzo se pokazalo da Sievert niti želi niti zna da upravlja firmom. Nakon teško položene mature ipak je bio veoma odlučan. Zahvaljujući samo dobrom finansijskom stanju svoje porodice mogao si je priuštiti lutanja u traženju pravog fakulteta. Poslije upisa na fakultet u Stockholmu 1914. god. nastavio je studije na Karolinška Slika 1. Rolf Maximilian Sievert Institutu i na Kraljevskom institutu za tehnologiju u Stockholmu. Uzalud je pokušao studirati medicinu i elektrotehniku. Nastavio je sa studijima astronomije, meteorologije, matematike i mehanike na univerzitetu u Uppsali. Taj fakultet je uspio završiti 1919. god. Tokom svog diplomskog rada Sievert se bavio ispitivanjem zračenja jednog preparata od radijuma. Kasnije je ta oblast postala njegova životna preokupacija. Sievert je doktorirao 1932. god. sa tezom «Metode za mjerenje rentgenskog, radijum i ultrazvučnog zračenja i istraživanja u vezi primjene istih u fizici i medicini» pisanom na njemačkom jeziku. U dodatku su navedene formule i tabele za izračunavanje raspodjele intenziteta kod izvora gama zračenja. Iste godine postao je asistent - profesor za medicinsku fiziku na Univerzitetu u Stockholmu. Na nagovor i pritisak porodice Sievert je ipak morao da se uključi u vođenje vlastitog preduzeća. Nakon prvog svjetskog rata, usput uz rad, 50 V. simpozij HDZZ, Stubičke Toplice, 2003 studirao je fiziku na višoj školi u Stockholmu i postao asistent na Švedskoj akademiji nauka. Još 1920. god. Sievert je saznao za mogućnost da se rentgenska zračenja i preparati od radijuma mogu koristiti u medicinske svrhe. Tada još nisu bili riješeni problemi definiranja i mjerenja apsorbirane doze. Sievert je razvio metode kako bi mjerio intenzitet rentgenskog zračenja. Sa jonizacionom komorom koju je sam izradio uskoro je mogao da mjeri određene doze zračenja. Tako se sada, u borbi protiv tumora i raka, tj. prilikom primjene jonizirajućih zračenja u medicini, moglo dozirati rentgensko zračenje. Sievertov dalji životni cilj bio je razvoj prikladnih metoda za zaštitu od zračenja. Pored naučnih i radnih zadataka Sievert se brižno brinuo i o svojoj brojnoj porodici. Ženio se dva puta i imao sedmoro djece. Njegov hobi pored uzgajanja kaktusa i sviranja orgulja bilo je sakupljanje i prepariranje leptira. Već 1919. god. Sievert je imao kontakte sa radiolozima, fizičarima, koji su koristili jonizirajuće zračenje u svom poslu i ponudio im svoju saradnju u pokušaju da se rješe fizički problemi vezani za upotrebu radijacije u svrhe dijagnosticiranja i terapije. Između 1924. i 1937. god. bio je šef Laboratorije za fiziku u Radiumhemvretoru. Godine 1937. bio je postavljen za šefa Odjeljenja za radijacionu fiziku na Karolinška Institutu, a 1941. god. postaje profesor za radijacionu fiziku na istom institutu. Ukupno 27 godina vodio je Institut za radiofiziku u Stockholmu do 1965. godine kada je penzionisan. Umro je 3. listopada 1966. god. od posljedica operacije na stomaku. Društvo za zaštitu od raka odlučilo je 1924. god. da nagradi Sieverta, kao šefa za Laboratorije za fiziku u Radiumhemmet-u koju je on praktično organizirao i financirao, i za razvoj laboratorije i humane primjene radijacione fizike u medicini. Pod vodstvom Sieverta laboratorija se razvila u svjetski poznat centar za radijacijsku fiziku. Godine 1938. aktivnosti se prenose na Karolinšku bolnicu gdje je formirano odjeljenje za radijacijsku fiziku. Tokom ranih dvadeseth godina dvadesetog stoljeća još nije obavljena standardizacija apsorbiranih doza za pacijente u bolnicama gdje se primjenjivalo jonizirajuće zračenje. Da bi se to stanje popravilo i reguliralo, Sievert je 1925. god. osnovao organizaciju koja je bila odgovorna za kontinuiranu kontrolu stepena doziranja zračenja u svim bolnicama u zemlji u kojima se obavljao tretman radijacijom. Kako je vrijeme prolazilo, program kontrole i nadzora (kako medicinske tako i industrijske) je proširen na sve poslove sa jonizirajućim zračenjem. 51 V. simpozij HDZZ, Stubičke Toplice, 2003 Slika 2. R. M. Sievert u svojoj laboratoriji Na inicijativu Sieverta švedska vlada je 1941. god. donijela prvi švedski Zakon o zaštiti od radijacije. Zakon je Odjeljenju za radijacionu fiziku dao zadatak da nadgleda i kontrolira njegovu provedbu. Sievert je bio 1929. god. jedan od glavnih inicijatora i osnivača danas poznatih organizacija: ICRP - Međunarodne komisije za radiološku zaštitu i ICRU - Međunarodne komisije za radiološke jedinice i mjerenja. Između 1920.-1940. god. Sievert je dao svoj najznačajniji doprinos na polju medicinske fizike. On je izgradio osnovu za određivanje i računanje apsorbiranih doza kod ozračivanja tumora. Razvio je nove uređaje za ozračivanje pacijenata i naveo značaj doprinosa sekundarnog i reflektovanog zračenja na pacijente i dozimetriste. Izumio je više dozimetara među njima i poznatu Sievertovu jonizacionu komoru. Tokom 1930-tih god. Sievert je prvenstveno radio na izučavanjima bioloških efekata jonizirajućeg zračenja, a posebno efekta malih (slabih) doza koje radiolozi primaju u svom svakodnevnom poslu, kao i ostalo stanovništvo prilikom djelovanja kozmičkog zračenja i prirodnog zračenja iz okoline. Nakon proba nuklearnih eksplozija u atmosferi radioaktivne padavine (fall-out) postale su svjetski problem. Prije nego je to pitanje javno izneseno, Sievert je taj problem već rješavao proučavajući podatke koje je prikupio izučavajući padavine koje su nastale od erupcije vulkana. Većinu svog vremena posljednjih dvadeset godina života Sievert je posvetio poslovima na rješavanju problema zaštite od radijacije. Načinio je planove za Švedski Institut za zaštitu od jonizirajućeg zračenja (SSI). Sievert je bio priznat i cijenjen na međunarodnom nivou. 52 V. simpozij HDZZ, Stubičke Toplice, 2003 Bio je predsjednik ICRP od 1956. do 1962. god. i UNSCEAR (Komisija za efekte od atomske radijacije pri Ujedinjenim nacijama) od 1958. do 1960. god. Sievertova komora ima slijedeće karakteristike: u najčešće korištenoj formi Sievertova komora ima centralnu elektrodu u obliku sfere ili cilindra načinjenu od legure magnezijuma (elektronski metal) koji je smješten u centar šuplje sfere od istog materijala. Unutrašnja elektroda fiksirana je u svoj položaj izolatorom od ćilibara. Ona se kroz otvor na vanjskoj sferi može naelektrizirati i dovesti na poznati potencijal. Taj otvor se zatvara poklopcem koji je opremljen štapom i koji ujedno služi i kao držač komore. Ako je komora izložena jonizirajućem zračenju, tada zrak u šupljini između unutrašnje i vanjske sfere postaje vodljiv preko formiranih jonskih parova. Električni naboj komore je reduciran zbog curenja nastale struje. Ona se može tada lako izmjeriti posebnim instrumentom na nekom udaljenom mjestu, npr. laboratoriji. Smanjenje električnog naboja je mjera za radijacionu dozu koju je komora primila. Takva komora se može dakle transportovati na druga udaljena mjesta bez bojazni da će doći do promjene očitavanja vrijednosti na njenom izlazu. Promjer Sievertove komore može iznositi svega nekoliko milimetara. LITERATURA Rolf Sievert, the man and the unit — Department of Medical Radiation Physics, Karolinška Institut Sweden. Paić V, Paić G. Osnove radijacione dozimetrije i zaštite od zračenja, Sveučilište u Zagrebu, Zagreb, 1983. Draganić I. Radioaktivni izotopi i zračenja, Knjiga l. Univerzitet u Beogradu, Beograd, 1981. ICRU Report 60, International Commission on Radiation Units and Measurements, Washington D.C., USA, Fundamental quantites and units for ionizing radiation 1998. Tomljenović I. Rolf Maximilian Sievert, XX simpozij JDZZ, Tara 99, Zbornik radova, Beograd, 1999 st. 35-38. LINKS:
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