SCIENTIFIC ÁND TECHNICAL REVIEW OF THE COMMISSION OF THE EUROPEAN COMMUNITIES

SEPTEMBER 1973 VOL. XII NO. 3 58 GIANCARLO BERTOLINI, FRANCESCO CAPPELLANI, GIAMBATTISTA RESTELLI

ION IMPLANTATION IN SEMICONDUCTORS

73 JAN G. SMEETS

ECOLOGY AND ENVIRONMENTAL HYGIENE

84 TECHNICAL NOTES

88 RECENT PUBLICATIONS ON INDUSTRIAL CHEMICAL ANALYSIS METHODS

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Any article published In this Review may be reproduced in whole or In part without restric• tion, provided that the source Is mentioned. On the vast construction site of the European Community, where ideally every one brings his own brick to contribute to the structure, work does not always proceed with the desired speed and organi• zation. Difficulties and problems arise both with the architects who design and supervise the building work and with the labour force which harbours a persistent nucleus of anti-Europeans. There has been no lack of noisy demonstrations of opinion from these people both recently and in the euro past. The typical anti-European, who has his own Euro-brick like everyone else, does not bring it to the common site to contribute to the construction but spectra feels only the irresistible urge to hurl it at the heads of those he thinks are responsible for the project.

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Like all large-scale and complicated undertakings, the Community of Europe has its convinced detrac• tors who are often in the dark as regards what has been done, what is being done, what it is proposed to do and why, and who are stubbornly determined not to know. Obviously having to help carry the bricks on The Commission of the European Commu• the site is not as easy or as pleasant as going to live nities or any persons acting on its behalf in a soundly constructed building but it is equally disclaim all liability with respect to the true that without labourers no one has ever managed completeness of the information contained to build anything. in this periodical as well as to any damage which might result from the use We should like to ask the typical anti-Europeans of information disclosed or of equipment, to devote to the construction of Europe just one tenth methods or processes described therein. of the interest and attention which they lavish on their house plans for themselves and their children. Picture credits : Cover : Gaston Bogaert, This would undoubtedly help them to proceed to a Brussels. profitable examination of their conscience. Pictures : pp. 63, 66, 67 : JRC Ispra ; pp. 73, 75, 76, 82 : Jan van de Kam, Griendtsveen ; p. 80 : Cas Oorthuys, Amsterdam.

Printed in Belgium by Maison d'Edition s.c 6001 Marcinelle Ion implantation 2) The purity of the material which is introduced does not depend on the in semiconductors original material and is very closely controllable. In thermal diffusion everything depends on the degree of purity of the materials used: e.g., residual impurities in the single crystal GIANCARLO BERTOLINI, FRANCESCO CAPPELLANI, are diffused together with the doping GIAMBATTISTA RESTELLI atoms. 3) Implantation is not an "equilibrium process" like thermal diffusion and it is not bound by the physicochemical ENERGIZED IONS can be used to formation by the introduction of impu­ properties of the solute/solvent (ion/ change the properties of materials: rities takes place on the surface of the target) system. It follows that concen­ this new technique is known as "ion semiconductors and extends to only a trations in excess of the thermal solu­ implantation". The required atomic very small depth below the surface (of bility limits can be obtained and species ionized and accelerated in an the order of μιτι or less); secondly, the atoms with a very low diffusion electrostatic field is fired at the material alteration of the original electrical velocity or zero solubility can be which is to be treated. The ions penetrate properties is useful when extremely small introduced in depth. the target and lose their energy in colli­ amounts of impurities are introduced 4) Basically ion implantation is a process sions with the atoms and electrons in the (from one atom per hundred million to which takes place at much lower solid until the rest energy is reached one per hundred atoms of the semi­ temperatures than diffusion, avoiding (thermal energy). This, briefly, is the conductor). the difficulties caused by the use of process. In the present state of the art, the high temperatures (500-700 °C as In 1954 Shockley, who with Brattain methods which can be used for "doping" against over 1 000 °C). and Bardeen shared the Nobel prize in are, in order of importance: 5) The ions penetrate the crystal as a 1956 for invention of the transistor, - thermal diffusion; directional beam; in this way the patented the use of an accelerated ion - introduction during the growth of the doped region is defined with remark­ beam as a means - in conjunction with crystal or the formation of an epitaxial able precision, contrary to what traditional processes - of producing elec­ layer; happens in diffusion where the iso- tronic devices, outlining the potential - alloying with a metal. tropy of the process causes leakage at advantages of a technology which was the edges of the mask which delimits only effectively developed at the indus­ The first method is by far the most the doping zone (Fig. 1). trial level at the end of the sixties. As used and it is mainly as an alternative is known, the manufacture of solid state to this method that ion implantation has On the other hand, the main disad­ electronic devices involves the introduc­ been introduced, even in industrial vantage of ion implantation must be tion of a specified quantity of electrically production. It may seem rather extra­ attributed to the slowing down of the active impurities into a semiconductor ordinary that such a recent technique ions during their penetration into the (e.g., silicon). The semiconductors under­ should be able to replace thermal dif­ semiconductor. The single crystal origi­ go a change in their original electrical fusion, which is braked by a vast amount nally has an ordered periodic structure properties which depends on the type of of development work and technological which determines its electrical properties. impurity. This is what is meant by the research. The energized ion penetrating this term "doping", which is the key process In fact ion implantation is not a collides with the atoms of the solid, for all solid state electronics. complete alternative but is only a which may receive enough energy to be With this system, combined with the substitute technique used in the produc­ displaced from their lattice position so creation of insulating layers and various tion of some devices or in certain phases that the bonds are broken and as a types of connections, it is possible to of the manufacturing process. result the characteristic regularity of the produce devices ranging from simple The advantages of ion implantation structure is lost. In extreme cases, if a diodes to complex integrated circuits compared with thermal diffusion can be sufficiently large number of atoms are which incorporate many thousands of itemized as follows: displaced, the solid changes from crystal­ line to amorphous. Fortunately this devices. 1) The quantity of impurities introduced, disadvantage can be largely remedied by The two basic characteristics of the the depth of penetration and therefore carefully heating the bombarded sample; "doping" process are, firstly, that trans- the concentration in the crystal are this annealing restores the crystal struc­ parameters which can be controlled ture and makes it possible to retain the precisely and independently through typical electrical properties of the chem­ GIANCARLO BERTOLINI, the intensity of the ion beam and FRANCESCO CAPPELLANI, the energy of the ions. By contrast, in ical species of the introduced ions. This is GIAMBATTISTA RESTELLI- diffusion it is possible to act on the still one of the main problems, however, Electronics Division, Joint Research Centre diffusion time and the temperature, as it may raise difficulties with some of the Commission of the European Commu­ materials. nities, Ispra Establishment. but not independently.

58 The theoretical studies on the influence In (a), because of the tremendous Electronic stopping increases linearly of ion bombardment in solids go back to difference between the masses, the ion with the velocity of the projectile, the fifties. The first experimental studies loses a small part of its energy at each whilst nuclear stopping has a bell­shaped followed about ten years later. Originally collision with virtually no change in its curve with a maximum at low velocity it was thought that the physical properties original trajectory. This process, termed values of the ion. It follows that the two of materials subjected to ion bombard­ "electronic stopping", is characterized curves intersect at an energy value which ment were substantially determined by by a low "specific energy loss" (i.e., per depends on the atomic numbers of the the damage caused by the slowing down unit of length travelled by the ion in the projectile and the medium (Fig. 2). of the ions. Only subsequently did it solid). Two parameters are used to charac­ become clear that under suitable experi­ In (b), the collision of the ion with an terize the ion penetration process: the mental conditions it was possible to "range" and the "penetration distribu­ obtain a predominant effect due to the atom in the lattice may, depending on tion". When the ion has reduced its physicochemical properties of the intro­ its severity, draw off a considerable initial energy to a value of about 10 eV, duced ions. amount of energy and sharply deflect the trajectory from its original direction. The it stops moving freely in the crystal and The first device obtained by ion process is called "nuclear stopping" and is captured by the cohesive forces of the implantation was a p­η junction in silicon is characterized by a specific energy medium. The route followed from the used as a nuclear particle detector and loss which is much greater than that impact on the surface of the solid to this made in 1962 by Alväger and Hansen. occurring in electronic stopping. The point is defined as the "range" which we will call R; Rp will be the "projected Between 1962 and 1964 the studies were atom, in the collision, can be displaced range" which corresponds to the projec­ generally of a fundamental nature. from its equilibrium position in the lattice tion of R along the extension of the Research, slanted more specifically and in turn causes chain collisions with towards the problem of "doping" semi­ direction of incidence of the ion (Fig. 3). the other atoms. This mechanism is conductors, gradually intensified between responsible for the ion bombardment 1964 and 1969 with the production of The projected range Rp expresses the damage, with the formation of highly commercial devices in small quantities. effective depth of penetration of the ion From 1970 ion implantation began to disordered regions around the path of inside the medium and is therefore more emerge as an important new technology the ion through the solid. It should be commonly used for practical purposes. of especial interest in the microelectron­ noted here that in crystalline structures The penetration distribution is determin­ ics field. In 1972 it became obvious from the defects generated in this manner ed by the fact that, since the slowing technical papers published or presented produce a marked change in the proper­ follows a random pattern, the ranges of at conferences and from industrial pro­ ties (optical, electrical, mechanical, etc.) the ions will not all be equal but will duction that this technology had acquired of the solid. Ultimately the original be distributed over a certain curve around its own niche in the semiconductor energy of the ion is exhausted by nuclear a most probable value. If we plot the devices industry. and electronic stopping. The fraction of individual R or Rp versus their proba­ energy lost in one or other of the proc­ bility, given a large number of ions all The potential advantages of industrial­ esses depends on the initial energy and having the same energy, their distribution scale ion implantation had originally on the atomic numbers of the projectile approximates pretty closely to a Gaussian attracted the interest of firms producing and the stopping medium. curve characterized by an average value ion accelerators. This resulted, between 1968 and 1970, in the development of commercial accelerators for implantation and subsequently in complete ion implan­ tation systems for industrial use. Dopant vapour Accelerated dopant ions

The physical process When the ion penetrates the interior of the solid it loses energy through two main processes: (a) collisions with the free or bound electrons in the solid; Si 0. ν ν ν ν ν ν (b) elastic collisions with the atoms which form the lattice. ^jjpzk^

Fig. 1: Owing to the directional precision of ï the ion beam, in implantation the doped area is exactly defined by the mask (SiOz). âzzzzzzzzzzzkzá In thermal diffusion the isotropy of the process T=1000°C T=25°C causes the dopant to diffuse under the edges of the mask. Thermal diffusion Ion implantation

59 Fig. 2: E1 represents the energy at which the Obviously ions with a mass equal to or greater initial energy of the ion is equally distributed than phosphorus and implantation energies of between the two processes (nuclear stopping the order of 100 ke V lose their energy almost in colour; electronic stopping in black). Some entirely in nuclear collisions. (Abscissa: values of E1 in the case of silicon and germa• energy of the incident ion; ordinate: loss of nium and for some types of ion are in ke V: energy per unit of path). boron phosphorus arsenic antimony Si 17 140 800 2 000 Ge 13 140 SOO 2 000

Table I: Ions impinging on silicon with an energy of 100 keV; values in Ångström units (1 Ångström = 10'8 cm).

Atomic Rp Rp ARp ARp Ion number calculated observed calculated observed

Boron 5 3 275 3 700 726 508 Phosphorus 15 1 228 1 200 350 380 Gallium 31 602 610 133 195 Arsenic 33 574 580 122 178 Antimony 51 448 450 71 123

The ion penetration decreases as the atomic number increases. The correlation between the values of the average "projected ranges" Rp calculated on the basis of the Lindhard theory and the values observed in experiment is good; some discrepancies occur for the variance ARp.

Values of the average "projected range" calculated in Ångströms for ions of different energies impinging on silicon

40 keV 80 keV 120 keV 200 keV 500 keV

Boron 1 413 2 695 3 802 5 588 13 000 Phosphorus 488 976 1483 2 514 6 000 Arsenic 263 471 677 1 097 2 800 Antimony 221 376 519 797 1 800

The penetration of the ions increases with the increase in energy.

60 Rp and a variance which we shall show as ARp (Fig. 4). Implantation makes it possible, in principle, to create any type of profile because one can continually vary the energy, whereas thermal diffusion is always characterized by a monotonic pattern of concentration versus depth. The two parameters Rp and ARp are sufficient to characterize fairly approxi­ mately the penetration of any ion into any substrate. A detailed theory of the phenomenon was originally drawn up by a group of Danish theorists headed by Prof. J. Lindhard; subsequent theories follow the lines of the original work done by these scientists. Fig. 3: 77;e path from the point of impact on of the direction of incidence is the "projected A vast collection of experimental data the surface of the solid (S) to the point where range" Rp. The coloured dotted line shows the was only later obtained with the develop­ the ions stop (continuous coloured line) is the trajectory of the incident ion. ment of extremely refined techniques for "'range" R; its projection along the extension the removal of thin layers of a specified thickness (of the order of 1/100 000 mm) from the implanted sample, together with the use of radioactive tracers. There Fig. 4: Figure A shows some typical penetra­ The curves also represent the concentration of is a good correlation between the calcu­ tion curves for ions of various mass and energy the ions as a function of the depth and can be lated and experimental values of Rp but (abscissa: depth of penetration Rp; ordinate: compared with typical thermal diffusion there are still some discrepancies between number of ions with range Rp). profiles which always show a monotonically the calculated and experimental values of Figure Β shows atom penetration curves decreasing concentration depth. The variance ARp (Table I). obtained through thermal diffusion with var­ ±Rp is obtained from the halfwidth of the ious temperatures or times (abscissa: depth I curve at -— of the maximum concentration. Until 1963 the phenomena of ion of penetration; ordinate: number of atoms e penetration in a solid were thought to be per cm3). V independent of its allotropie form The implanted ions are distributed according (amorphous or crystalline), even though to a penetration curve which is roughly as early as 1912 J. Stark had foreseen an Gaussian.

Β

61 effect of the interatomic fields on the potential obviously keeps the angle of al defects which in their turn generate motion of charged particles in solids. incidence of the ion low in relation to the dechannelling of the ions. The probabi­ It was in 1963 that computer simula­ axis of the channel. This angle, called the lity of dechannelling increases with the tion of the phenomena enabled two critical angle, is in inverse proportion to integrated dose (number of ions which American scientists, Oen and Robinson, the energy of the ion and directly propor­ have struck the crystal). to show that the ion penetration process tional to the product of the atomic The distribution of the ions which was substantially different in crystalline numbers of the ion and of the atoms of penetrate a single crystal under channel­ the crystal (Table III). solids, for these permitted a new phenom­ ling conditions differs substantially from enon termed "channelling". Experi­ By changing the direction of the ion that obtained in an amorphous solid or mental confirmation was obtained almost beam one can, roughly speaking, make disoriented crystal. at the same time by a group of scientists the crystal beh ave like an amorphous The atoms which remain channelled at Chalk River with implantation in solid as regards the ion-stopping effects, until they have completely lost their single-crystal aluminium and tungsten. This occurs, in the case of crystals with energy correspond to the maximum Channelling in single-crystal germanium a diamond-type lattice, when the beam penetration of the crystal and, depending had been observed, but not identified, is set 8° out of ine with one of the main on the extent of the dechannelling years before by two Russian scientists. crystallographic axes. processes, may or may not form a peak. The explanation of channelling is based Alterations of the crystal order, for The parameter used to characterize the on two considerations, the first of which example, interstitial atoms which obstruct channelling peak is the maximum range R p 7 Tne is the degree of anisotropy of the crystal­ the channels, reduce the magnitude of max ( ig· )· dependency of Rmax line solids. If we observe a crystalline the phenomenon ("dechannelling"). The on the square root of the energy confirms lattice from different crystallographic surface of the crystal causes dechannel­ that for a well-channelled ion the predom­ directions it can be seen that some ling either because inevitably some of inant mechanism consists in collisions directions are more open than others, the incident ions impinge directly on the with the electrons of the solid. Consider­ forming a system of free channels for the atoms of the lattice or because the able difficulties are encountered, howev­ passage of the ions (Fig. 5). This is surface itself easily accommodates disho- er, when we try to find the value of Rmax especially true of lattices in which the mogeneities and impurities. These initial with variation of the atomic number atom has a higher coordination index collisions give rise, moreover, to structur­ of the projectile and of the different and which are therefore more densely populated, for example, the diamond and zinc blende type lattices, into which the most important semiconductor materials Table II: Depth of penetration of the ions in the solid. Slower channelled ions (such as Sb+, crystallize. compared with As+) have a lower specific energy loss and penetrate deeper into the crystal. The second consideration is that the Energy Rmax Direction of repulsion potential (coulomb) which Ion Rp exists between the ion and the lattice keV μΐϊΙ μΐΏ channelling atoms keeps the ion at some distance from the atoms when the energy compo­ Boron 60 0.21 0.92 (110) nent perpendicular to the direction of Arsenic 200 0.11 2.8 (110) motion of the projectile, and therefore to Antimony 200 0.08 4.3 (110) the row of atoms forming the channel, is less than the repulsion potential supplied by the row itself (Fig. 6). This occurs at suitable values of lattice spacing and ion direction and velocity. In such cases the ion encounters no break, in the Table III: Critical angle in silicon calculated on the basis of the Lindhard theory for different repulsion potential between the atoms crystallographic directions. The maximum angle of entry, in relation to the channel axis, at in the row, and the channel will look like which the incident ion is still channelled increases with the atomic number and the decrease in an open tube inside which the ion will be ¡on energy. Some crystallographic directions are more "open" than others, which means that contained through successive correlated the incident ions channel with greater or less ease. interactions at small angles. There will therefore be minimal loss of energy Ion Energy (keV) < no > < m > < 100 > through nuclear interaction and the electronic type of slowing down will 50 3.7° 3.2° 2.9° predominate. The range taken by the ion will therefore be considerably longer Boron 100 2.6° 2.3° 2.0° (up to two orders of magnitude greater) 500 1.2° 1.0° 0.9° than those observed in the same solid where there is no channelling (Table II). 50 5.2° 4.4° 4.0° Arsenic 100 3.7° 3.1° 2.8° The fact that the transversal energy 500 1.6° 1.4° 1.3° component is less than the repulsion

62 crystallographic directions in a partic­ ular solid. Up to now no method has been devised to calculate Rmax with reasonable accuracy, but the problem is being actively studied.

From what has been said so far, the reader can see which parameters influence the distribution of ion penetration plotted against the depth within the solid (concentration profile or "physical profile"). A particular physical profile can be made by acting on the following variables: - energy of the implanted ion; a) - atomic number of the ion; - direction of incidence of the beam on the crystal; - temperature of the sample, and dose which in addition makes it possible to regulate the absolute value of the concentration of the introduced ions. In such applications as the manufacture of electronic devices, however, it is important to know the distribution ver­ sus depth of concentration of the electrically active atoms: this is known as the "electrical profile". This does not necessarily correspond to the "physical profile", since the introduced ions may be associated in complexes with the structural defects (which also have electrical activity) caused by the implan­ b) tation, or may not find themselves in a suitable lattice position (Fig. 8). It is known that the introduction of Fig. 5: A diamond type lattice (typical of such electrical activity for them. This does atoms which have an outer electron shell, semiconductors as silicon, germanium, gallium not occur in the case of ion implantation arsenide) displays obvious channels when it is and therefore a valence, differing from for two reasons. First, at the moment oriented in a main crystallographic direction. that of the atoms constituting a semi­ when the introduced ion reaches thermal In a) direction <( /// y ; in b). the direction energy it may be in any lattice position. conductor induces well-defined electrical rotated by an angle of 7° to the <( III y axis. properties in the semiconductor. Thus Secondly, the structural defects resulting in the lattice of a silicon or germanium from bombardment, besides being them­ single-crystal (group IV in the periodic selves electrically active, act in combina­ table) the presence of atoms of group positions, i.e., sites normally occupied tion with the introduced ions or with the III, which tend to capture an electron, by an atom of the semiconductor) in a impurities present in the semiconductor, gives rise to predominant conductivity crystal with almost no structural defects. modifying the effect due to the chemical for the transfer of holes (type p) and The presence of impurities in other species of the implanted ions. conversely the presence of elements forms, e.g., in the form of precipitations, The structural defects are moreover of group V, which tend to lose an elec­ strongly affects the electronic processes extremely critical by reason of the tron, gives rise to predominant conduc­ in the semiconductor but not in the way modifications they produce in the salient tivity for the transfer of electrons (type desired. The traditional "doping" characteristics of the semiconductor n). These impurities are usually termed methods are based on processes which such as mobility, average carrier life­ "dopants"; common η-type dopants take place while heterogeneous equilib­ times, etc., which contribute vitally to (or donors) are P, As, Sb; p-type dopants ria are being established at the inter­ the performance of the devices. (or acceptors) are B, In, Ga. In order face. Thus in thermal diffusion, at the to produce the desired effect the dopant high temperatures used for the process, Every incident ion is, directly and atoms must form a solid solution in the the introduced ions are able to reach the through a series of chain collisions semiconductor, occupying well-defined lattice position which is thermodynam- between the atoms of the lattice, res­ lattice positions (mostly substitutional ically correct and has the appropriate ponsible for knocking a large number of

63 UJ

Fig. 6: a) Ion A penetrating at an angle of incidence smaller than the critical angle is kept on course by a series of successive small angle interactions within the channel. Ion Β penetrating at an angle of incidence greater than the critical angle is rapidly dechannelled through nuclear collisions. Ion C, although it impinges in a direction parallel to the channel, is not channelled as it directly strikes an atom on the surface. b) The projection, on a plane perpendicular to the direction of incidence, of the trajectories of ions directed parallel to a crystallographic axis clearly illustrates the channelling phenom­ enon. The figure refers to the results of calculations by Robinson and Oen for copper ions impinging on single-crystal copper.

Amorphous peak Channelling peak t 1/ Λ -"/^\ / » / ι Fig. 7: The penetration curve of channelled / Ι Ν / I ions in a crystal has three zones. The first (A) 1018 1 / i shows the atoms immediately dechannelled at J \ the surface and corresponds to the curve of y distribution in amorphous material. The -- __^-" \ 1 second (B) corresponds to the ions dechan­ \ 1 nelled along the path. The third (C) represents IO" \ 1 the ions which remain channelled until they \l have lost all their own energy. 1 A Β C \ The dotted curve represents an almost ideal case ; the continuous curve represents a typical 1016 j 1 real case, for example of single-crystal silicon. Abscissa: depth of penetration; ordinate: t 1 ions per cur . Rmax

64 atoms of the bombarded material out of their lattice position, thus forming vacancies and interstitials (Fig. 9). The minimum energy required to form a Frenkel defect, that is a vacancy­ interstitial pair, varies from one type of crystal to another but is of the order of 10­20 eV. Consequently, an ion with an initial energy of a few tens of keV generates some thousands of defects of this type, for example, a 40 keV Sb + ion displaces on average some 2 000 silicon atoms. The number of atoms displaced varies with the energy of the particle, with the nuclear collision cross­section and above all with the degree of channelling of the ion beam in the crystal. The damage increases with the dose until the originally crystalline substrate becomes amourphous. Where the amorphous state extends to the 0.05 surface and modifies the optical reflec­ tivity of the material (Fig. 10) this change actually becomes visible. Fig. 8: Physical and electrical penetration electrical profiles were obtained by measure­ profile of 80 keV arsenic ions in silicon. ment of resistivity and differential surface The number and spatial distribution of The physical profile was obtained by tracing Hall effect and sectioning by anodic oxidation. 3 the atoms displaced from the ions have the As by radioactivation: As"h(n, ­()As7li. The continuous line shows As atoms per cm , The radioactive tracer was then assayed in the the dotted line the number of electrons per been extensively studied both theoreti­ 3 cally and experimentally. The experi­ si/icon layers (140 Angström per volt), and cm . The depth of penetration (in \un) is mental studies have used various tech­ removed through anodic oxidation and selective plotted on the abscissa. niques ranging from the study of the dissolution using an automatic apparatus. The optical properties to the diffraction of low energy electrons, from electron microscopy to X­ray diffraction and to recent techniques based on the channel­ ling of H+ or He+ particles with energies Table IV: Possible reactions which determine the lattice position of an ion X implanted in silicon. of 1­2 MeV. At the end of the implantation the ion X is in a particular position surrounded by substitutional silicon atoms Sis, interstitial silicon atoms Si\, vacancies V, general defects D. According to the theoretical calcula­ tions, the defects will be non­uniformly distributed along the path of the ion. Substitutional reactions The curve which expresses their distri­ bution versus depth in the crystal is 1. The ion (free or interstitial) reacts with a vacancy analogous to the ion concentration pro­ becoming substitutional X or X, + V -> xs file but lies appreciably nearer to the 2. The ¡on becomes substitutional during the reordering surface. of the lattice disorder Ideally, in order to use the electrical 3. The ion becomes substitutional through collision during the final stage of the range X + Sis X -1 Si, properties of the implanted layer the -> s atoms would be implanted in the correct Interstitial reactions lattice positions in an almost defect­ free crystal. This condition can be more 4. The ion migrates into an interstitial position X, ­> X I V or less completely achieved through an 5. The ion becomes interstitial during the reordering annealing process in which the sample of the lattice disorder is heated in a vacuum furnace or in an 6. Watkins displacement reaction X, + Sii - Xl + Sis inert atmosphere at a given temperature for a given time (typically, for semi­ Other reactions conductors 300­900 °C for 10­60 min­ 1. The ion moves into an irregular lattice position utes). (precipitates from the solid solution) Xs or Χι -> X

The characteristic annealing temper­ 8. The ions interact with one another to form pairs Xs -1- x. -> Xs X, atures vary considerably depending on 9. The ion interacts with defects to form complexes Xs + D -► Xs - D the degree of disorder. For low doses (ion­vacancy pairs) Xl i D —► Χι D where the damaged zones around the

ft 5 o o o o o o

various ion paths are not superimposed, Fig. 9: During its journey through the crystal the reordering takes place at relatively low lattice the incident ion may collide with a temperatures: in germanium and silicon lattice ion and displace it into an interstitial at about 200° and 300 °C respectively. position, thus creating a vacancy; in this way For doses sufficient to cause the forma­ a Frenkel defect or pair (vacancy + inter­ tion of an amorphous layer higher stitial) is formed. At the end of its trajectory, temperatures are needed — in the above the incident ion may either be in an interstitial case about 400° and 600 °C respectively. position (case A) or in a sttbstitionalposition, having projected a lattice atom into an inter­ The reconstitution of the single­ stitial position (case B). crystal phase is most probably due to a A, A1 = incident ions; process of epitaxial reordering starting Β = ion in substitutional position; from the crystal under the amorphous C, Cl = ions in interstitial position; zone. D = vacancy; The transition of the material from the D­C1 = Frenkel defect. amorphous to the crystalline state may be not enough to dispel the more complex defects caused by the evolution of primary defects (vacancies­interstitials) which associate to form dislocations, dislocation loops, etc. In view of the disproportion between the number of defects and the number of ions intro­ duced, it is obvious that even a small residual fraction (e.g., 0.1 %) can deci­ sively alter the electrical properties of the implanted layer. Hence it is some­ times necessary to use annealing temper­ atures higher than those required to reorder the lattice. During the annealing, the implanted ions move into well­defined lattice

Fig. 10: Photograph of a silicon single crystal implanted at higher doses than the amorphi­ zation dose. Note different surface reflectivity. The doses (ions/cm1) required to render single­crystal silicon amorphous with various ions of 40 keV energy are: boron 2­ 10u'; phosphorus 5 10u; arsenic 2 · 10u; bismuth 5 ■ IO'3.

66 positions through complex interactions damage followed by annealing at about The energy imparted to the ions usually with the crystalline solid. 600 °C. ranges from 40 to 400 keV. The values The group V donor elements tend (as In the foregoing examples reference most generally used are around 100 keV to about 90 % of the total number) to has always been made to implantation (Fig. 11); high-energy (MeV) accele­ occupy substitutional positions, whilst in silicon, since this material has been by rators are rarely used. the group III acceptors have an appre­ far the most closely studied, but similar The ion currents on the target vary ciable substitution fraction (30 %); the phenomena have been observed else­ between tenths and tens of micro­ remainder are partly in interstitial where, for example, in germanium. amperes, i.e., from 6 · 10' ' to 6· 1013 positions (30 %) and partly in irregular A discussion of the atomic position is ions a second. lattice positions. It seems to be proved, difficult in this context, since it would A typical ion implantation accelerator however, that the final position of the inevitably turn into a list of cases itemized is composed of an envelope under high implanted atom is determined by the according to the nature (type of ion) and vacuum in which we may distinguish the treatments applied after the ion has been the conditions (dose, temperature during following components: slowed down by thermal energy, and not implantation, annealing temperature) of (a) ion source: consists of a chamber by the events which take place during the implantation. Some patterns have into which the substance is intro­ its slowing-down in the crystal. been brought to light, as we have already duced in the gaseous state and ionized indicated, but there is still no general by various processes. The ions thus On the basis of experimental data a theory of the phenomenon. generalized model has been formulated formed are extracted from the To conclude, there is still the problem which examines various types of reaction chamber using a suitable electric field, of whether completely channelled ions which can take place between the which, in the simpler types, deter­ have a preferential lattice position by introduced atoms, lattice atoms and mines the final energy of the ion. comparison with non-channelled ions. defects, and which finally determine the (b) analysis system: the ion beam which The question is still open since the rele­ lattice position (Table IV). As a general leaves the chamber generally contains vant data are extremely sparse. rule it has been observed that a higher a certain number of ions from which the desired species will be selected. electrically active fraction is obtained Ion accelerators when the degree of damage to the This is done by means of a magnetic implanted zone is such as to make the The first studies on ion implantation field or an electric field combined crystal amorphous. In the reordering were carried out with the then existing with a magnetic field (Fig. 12). In of the lattice there is the strong possi­ isotope separators. This limited the the first case, when a certain path bility of a substitution reaction between range of available energies, because on has been defined by means of slits, a doping atom and a vacancy. For average these instruments accelerated the for a given ion energy and for a given example, in implanting ions which ions to an energy of the order of 40 keV. magnetic field, only the ion species produce a low degree of damage, e.g., Later, increasing interest in implan­ with a specific charge/mass ratio boron, it has been found useful to make tation led to the planning and develop­ will follow the trajectory that passes the silicon amorphous before annealing, ment of special accelerators. through the slits. In the second case, by bombarding it with ions which do not confer electrical activity on the semiconductor. After implantation and annealing only 10 % of the introduced boron atoms are electrically active; the value leaps to 80 % after rendering amorphous with argon or neon ions.

Particularly in implantations with an intermediate degree of damage, contained in structures of the dislocation type, on annealing, these structures can trap the implanted ions and prevent them from reaching substitutional positions. It is therefore understandable that the elec­ trically active fraction, produced by implantation in semiconductors heated to 250-300 °C in which there is a contin­ uous partial repair of the damage, is decidedly lower than that obtained with low-temperature implantation and heavy

Fig. 11: 100 ke V ion accelerator fabricated by the Electronics Division of the Joint Research Centre, Ispra.

67 mass separation is effected by the antagonistic action of an electric field and a magnetic field set at right angles to one another (velocity filter). The second system is more economical than the first, the magnet in this case being much smaller, and although it operates a less distinct separation of the masses than the first system, in many cases it suffices. (c) beam deflection system: in order to bombard the sample as evenly as possible, the ion beam sweeps an area containing the sample to be 3 implanted. This is done by means of H 6 / /r- two pairs of flat electrodes set at γ- s—' ___ i>fi 90°, to which appropriate potential Λ-Γ -ΫΖ^ —- ^ differences variable in time, will be s 4 applied. (d) target chamber: this part of the equip­ ment is designed to contain the implantation sample and the devices Fig. 12: In the upper accelerator diagram mass silicon wafers of 20-30 mm diameter. The which control its orientation in selection is obtained by means of a magnetic total duration of the operations is short­ regard to the ion beam, and also its field which (with a given energy and a given ened, allowing a processing rate of 100- temperature. Owing to the variety of value of the magnetic field) focuses on to the 200 samples an hour. conditions in which implantation can outlet slit only that ion species with a certain take place, this part of the equipment charge/mass ratio which is to be implanted. When one has to manufacture a large varies according to the purpose for In the lower diagram, the analysis is done by number of small devices in high-density which it is intended. The basic means of the antagonistic action of an electric on a single silicon wafer, or to fabricate requirements for a target chamber field E and an orthogonal magnetic field H. The integrated circuits, two different technol­ for research and development work only trajectory not deflected by the opposing ogies may be applied. forces due to E and H is that of the ions are as follows: which have a given velocity (imposed by the The first consists in using mechanical - high vacuum (10~6 torr), "clean", values of E and H) and which therefore, since or, preferably, chemical masks (e.g., i.e., free from organic or any other the energy imparted to the ions is constant, layers of Si02 grown on silicon crystal, vapours that might contaminate possess a certain mass. the structure of which is determined by the sample surfaces; I: ion source; photo-engraving processes) which are - a means of heating (500 °C) or 2 : accelerating and focusing system ; bombarded uniformly by the ion beam. cooling ( — 200 °C) the sample 3: magnet; The second consists in the possibility during bombardment; 4: velocity filter; of producing one or more ion beams with - a means of treating several samples 5: beam sweeping system; a diameter of the order of a micron or without having to raise the cham­ 6: sample; less. These beams, suitably controlled and directed by means of electronic ber to atmospheric pressure be­ 7: slit. tween the treating of one sample deflection systems, are able to "write" and the next; directly on the semiconductor without the - a means of mounting the sample use of masks, structures or complex on a goniometer enabling a crystal­ purposes, the tendency is to make circuits. The obvious advantage of this lographic direction of the sample them capable of performing as many system is that it can be directly controlled to be aligned with the ion beam. functions as possible, even at the cost by a computer, a fact which, if developed of the machine's simplicity; but the to the extreme, would lead to a complete The implantation sample is part of principle is different in implantation automation of the manufacturing proces­ a "Faraday cup" type of structure, systems for industrial uses. In this case, ses in microelectronics. which enables the number of ions striking the ion-beam accelerator and analyser the target to be assessed from the current are reduced to their basic components reading. By connecting the Faraday cup Application to semiconductor devices in order to optimize reliability and safety to a current integrator, it is possible and to speed up the operations. For to stop the implantation automatically The importance of ion implantation in instance, in the case of the target cham­ when a certain charge, corresponding to the technology of electronic semicon­ ber, great importance is attached to the a pre-set number of ions, has been ductor devices derives from the differ­ possibility of housing and treating a reached ences, outlined in the introduction, large number of samples. In a typical between this process and thermal diffu­ Industrial implanlers — When fabricating implanter for industrial production, the sion as methods of "doping" semi­ implantation accelerators for research target chamber can hold about 40 conductors. It is worth noting that at

68 present the range of applications is - possibility of using one accelerator for and high amperages) depends on the expanding rapidly. On one hand devices several types of dopants. concentration profile and its uniformity basically intended to be produced by In terms of performance of conven­ along the surface. thermal diffusion are optimized by the tional devices, the advantages listed Reproducibility and production yield introduction of steps obtained by above take the form of improvement in are higher owing to better control and ion implantation; on the other hand, three basic characteristics: greater uniformity of the doping. designing draws new potential from the Some of the devices developed by greater degree of freedom that ion - high frequency response; means of ion implantation are listed in implantation allows in the doping of - ability to withstand high power values; Table V; the list is far from exhaustive, semiconductors, and devices with totally - reproducibility and production yields. and is only intended to exemplify some new characteristics become feasible. The The high frequency response is limited greater flexibility of the doping process of the advantages discussed above. by the time required for carrier transit and better control of the basic param­ MOST — A more detailed treatment through the active region of the device, eters of the devices are the two factors has been reserved for MOST devices, and by the parasitic capacitances and which determined the introduction of both for historical reasons, because resistances, which depend on the geome­ implantation as an industrial pioduction they were the first to be made by implan­ try and the concentration profiles of the technology for silicon devices. In the tation on an industrial scale, and doped zones. One example of the advan­ case of compound semiconductors the because it is this category of device which tage achievable is given further on in the advantage is still more obvious, since has hitherto chiefly benefited from the detailed comment on the implanted with thermal diffusion it is often impos­ advantages provided by the use of ion MOST (Metal Oxide Semiconductor sible to introduce the desired doping implantation (Fig. 13). In the conven­ Transistor). impurities without at the same time tional MOST, the tolerances in the altering the structure of the semiconduc­ The ability to withstand high power masking process and the influence of tor with consequent deterioration of the values (high voltages without rupture, lateral diffusion are such that the overlap electric characteristics. This is due to the decomposition phenomena which occur in the material at the high temperatures Table V: Characteristics of the devices obtained through ion implantation. required for thermal diffusion. Resistors Possibility of obtaining high resistivity with It should be noted that implantation good reproducibility, uniformity and increased is compatible with all the technological value of discharge voltage to the substrate. processes already in use in the manu­ Small dimensions with advantages in the facture of these devices, and could be case of complex circuits. introduced either as an integral part of the process or as a process comple­ Diodes: menting or — in some cases — replacing thermal diffusion. — solar cells Junctions very close to the surface are obtained — nuclear radiation which minimize the radiation "entry windows ". From a strictly technological point of detectors It is possible to obtain uniform doping over view, the main advantages of the diffu­ an extended area. sion process may be summarized as — variable capacity The relation between the diode capacity and the follows: (varactor) diodes applied voltage can be predetermined within - a wide choice of doping elements; very broad limits by varying the concentration profile of the implanted ions. - possibility of varying the concentration profile to a wide degree, independently — IMPATT (Impact Junctions are obtained in which the tendency to Avalanche Transit form microplasmas is reduced by the uniform of the temperature; Time) diodes depth of penetration of the implanted ions. - high precision control of the doping This characteristic is particularly useful because down to the lowest levels with optimum these diodes operate with electric fields close uniformity even on surfaces several to the discharge level. 2 cm in area; — photodiodes The yields are improved from 10% to 90% owing - concentration profile not influenced by to the improved uniformity and reproducibility the presence of defects (e.g., disloca­ of the doping. tions) in the semiconductor; - use of relatively low temperatures, MOST (Metal Oxide Lower parasitic capacitances are obtained and which reduces the risk of introducing Semiconductor therefore it is possible to operate with higher unwanted impurities by diffusion and Transistor) frequencies; spoiling the characteristics of the greater compactness and density of devices in initial material (average carrier life­ complex circuits: time); lower energy consumption; improved control of characteristics; - absence of lateral spreading of the better reproducibility; dopant when introduced through a higher production yield. mask;

69 between the gate electrode and the other electrodes is, in most cases, comparable with the width of the gate electrode (a few microns). This gives rise to parasitic Li interelectrode capacitances which limit the frequency response and therefore the Si performance of the MOST. Using ion implantation, the source and drain regions adjacent to the gate electrode are Si 02 produced by implanting phosphorous in "ir— high doses (~ 1015 ions/cm2); the η [ΖΖΖ^ΖΖΖΖΓη resulting zone is perfectly aligned with the edges of the gate electrode. The gain thus obtained, in the form of a reduction of the parasitic capacitance by as much as a factor of 20, enables the implanted :·.'.·."·.".■ Iv-ïteï^.«.·;:·. MOST to operate regularly at frequencies & 13 ρ;•^ r of over 10 GHz. In addition, with the '■ ''//////// precision obtainable in the definition of the implanted zone and in the thick­ ness of the doped zones, it is possible P+ to reduce the overall size of the transistor, thus achieving greater compactness, ψ 4* ^ ^ "^ V V V" V ^ greater density of the components (up to three times that of the diffused MOST) and less energy consumption, and to obtain high reproducibility of the charac­ teristics and hence a higher production e yield. The practical results of the above are applied to the manufacture of integrated ζ Sä η W/E» circuits of the MOST type, used for various devices, e.g., computer memories, pocket computers, clocks, etc. f To conclude this short report, a word must be included on bipolar transistors, Si02 by far the most commonly used device. T^TW "^^ Much research is being done in this field, but the results have not yet led to an industrial manufacturing process. For production purposes, however, implan­ tation has already found a place as a method of accurately controlling the quantity of dopant which is subsequently Fig. 13: Diagram showing fabrication of a electric contact between the diffused displaced by diffusion, thus obtaining MOST device (more specifically, a MOSFET,) source and drain zones and the zone with mixed diffusion­implantation technique. directly underlying the gate electrode. a better production yield. (a) The source and drain contacts are first This connection is effected by implanting prepared by phosphorus diffusion (I: a high dose of phosphorus and then The use of ion implantation to dope source; 2: drain; Si: high­resistivity ρ annealing, which produces a highly compound semiconductors offers ex­ silicon). conductive η zone. tremely attractive prospects, which result (b) The zone between the source and drain (e) In the completed device the source and from the following facts: is then implanted with boron in order to drain zones are cleanly aligned with the ­ compound semiconductors are widely gate electrode, with consequent reduction obtain a thin layer of type­p material with used in the field of microwave devices of interelectrode capacitances. higher conductivity (channels). and optoelectronics as light emitters (c) A new layer of oxide is then grown (f) This is clearly shown by comparing the and detectors; (thickness of the order of 500 k) in the analogous zone of a diffused MOST, gate electrode zone, and the source, drain where the overlap between the gate ­ there are many obstacles stemming and gate electrodes are produced by electrode and the others is noticeable from the characteristics of these mate­ aluminium evaporation. ( I : gate electrode ; ? : source ; 3 : drain). rials which cannot be overcome by (d) The gate electrode is typically Ι μ wide. using the traditional diffusion techni­ The device is now complete except for the ques.

70 Although implantation is not as There are, furthermore, other aspects of advanced in this field as in the case of the "planar" technology used on silicon silicon, the principal applications for which would be directly applicable to Fig. 14: lon implantation is a technology which devices lie in the production of doped compound semiconductors when ion may be compared to a tree whose roots feed layers, the controlled introduction of implantation is used. on the existing knowledge in the field of atomic species which act as luminescent technology and fundamental physics. The Extensive case records exist at the branches represent the branches of science centres, and the creation of zones which laboratory level on the implantation of and technology to which this process has are rendered insulating by radiation luminescent centres in GaP and ZnTe brought solutions for old problems and has damage in order to separate different and of dopants in GaAs, InAs, InSb, offered fresh developments. active regions on the same substrate. CdS, CdTe, ZnTe and SiC.

Simulation of radiation damage v: ^ ; in materials y

Optical and magnetic properties of implanted films \

Chemical New and improved and physical behaviour electronic semiconductor of implanted ions devices ION IMPLANTATION

Physics of ion/crystal Ion accelerators interactions

/

Production Data Data on Data on the effects of accelerated ions on radiation damage the crystalline structure of impurities of matter in materials

71 The advantage of being able to use that it could be as widely applied in any type of ion regardless of its solubility other fields, but its potential is equally in semiconductors is obvious. For promising. example, the conversion of CdS from n Particularly noteworthy are the pros­ type to ρ type (an important stage in the pects in the field of the optical and manufacture of devices based on CdS), magnetic properties of materials. It has not feasible by diffusion, has been been shown that the refractive index achieved by implanting bismuth ions. of dielectric materials can be varied very In addition, because the defects can be accurately, by means of ion implantation; annealed at a lower temperature and this is of particular interest in the devel­ for a shorter time, the degradation opment of integrated optical circuits. (decomposition with loss of stoichiome- By using a similar technique it is possible try) produced by the high temperatures to modify thin films so as to control typical of diffusion is avoided. their magnetic properties; such a process One of the problems of compound could be used in the technology of semiconductors is the complexity of the superconductors and magnetic-bubble damage caused by the slowing down of memories. the ions in the solid. The electrical Other interesting applications are being activity of the defects introduced has found in the field of materials for nuclear been utilized to produce, by bombard­ uses. They depend on the possibility of ment with 100 keV protons, donor levels simulating, by ion bombardment, the in GaAs and high-resistivity layers in effect of high neutron fluxes on the pro­ ZnTe. The existence of acceptor or perties of the materials; an irradiation donor levels introduced by bombardment 5 2 with ~ 10' ions/cm is equivalent to often tends to conceal the effect produced an integrated flux of 1020 .. jfj2i fast by the chemical species of the implanted 2 neutrons/cm . Specific applications ion and to complicate the annealing concern void formation processes and process. A great deal of work is being gas emission from the structural materials carried out to throw more light on the of nuclear reactors and, in the field of behaviour of these systems. thermonuclear fusion, simulation of pressure vessel damage done by 14 MeV Summary neutrons. In this article, ion implantation has In the field of fundamental research, been presented as a complementary and the discovery of this technique has led sometimes alternative technique to ther­ to a far greater understanding of ion/ mal diffusion for the doping of semi­ crystal interaction processes and of the conductors. The explanation of the chemical and physical behaviour of physical process has shown the reader atoms introduced into different matrices. why it is a highly flexible and potentially Another contribution was the discovery valuable method. of ion channelling in single crystals, which disclosed a new branch of research As regards fabrication of the devices, and created a powerful instrument for we have confined ourselves to those diagnosing the position of atoms in a that have already been favourably asses­ crystalline matrix. sed and have found uses in industry which, after all, is the real test bench for Altogether, ion implantation is an any new technology. The material is excellent example of how a new technique continually being developed, and it is can help to stimulate studies and applica­ foreseeable that in 7-8 years time nearly tions in various scientific fields (Fig. 14). all the devices will include one or more ion implantation stages in the production EUSPA 12-9 process; the prediction is supported by the fact that this new technology pushes components electronics further along the References: (1) G. DEARMALEY: "Ion road it has already taken and which it bombardment and implantation", Reports appears bound to follow, towards greater on Progress in Physics, 32, part 2, 1969, device density, reliability and response p. 405. (2) J.W. MAYER, L. ERIKSSON and J.A. DAVIES: "Ion implantation in velocity and lower energy consumption. semiconductors", Academic Press, 1970. Our primary aim was to illustrate the (3) J. STEPHEN: "Ion implantation in semiconductor device technology", 77re use of ion implantation in the field of Radio and Electronic Engineer, 42, n. 6, semiconductor devices. It is not certain 1972, p. 265.

72 Ecology and environmental hygiene

JAN G. SMEETS, Health Protection Directorate (Directorate-General for Social Affairs) of the Commission of the European Communities.

Fig. 1: Man in an attempt to return to a place in his natural habitat * This article appeared in Dutch in Natuuren Techniek, 40 (1972), where he is in harmony with his environment. Nr. 9, pp. 441-453.

73 Ecology and ecosystems closely dependent on the physical, abiotic environment in which it lives and According to the usual definition, the with which, under normal circumstances, science of ecology or synecology ' means it forms an indivisible whole. Tansley (4) the study of the relationship between called this unity of the biocoenose and living beings and their environment and the biotope — under natural conditions each other. This term was suggested in - the ecosystem (biogeocoenosis). 1896 by the German biologist Haeckel (1 ) in order to distinguish ecology from Ecology is therefore a composite other biological and allied natural science. The consequence of increasing sciences, such as plant and animal specialization in the sciences, each physiology, systematics, sociology, agro- leading to its own highly specialized geology, etc. Because of its many facets, research, was that even a century or ecology is a synthetic science, made up more ago it was impossible, both liter­ of different disciplines. Ecological re­ ally and figuratively, to see the commu­ search is just as old as the research done nity of the wood for the trees. Insufficient in the numerous fields which form a part attention was paid to the interrelation of it. between the biocoenosis and its habitat, the biotope. Ecology is not a new science, but it is a topical one, as result of all the anti- This negligence was most in evidence ecological threats and dangers to which where human intervention led to the the human, plant and animal environ­ introduction into a particular ecosystem, ment is exposed to nowadays. alongside natural cultures, of cultures Though it is really stretching the term originating from other ecosystems with ecology somewhat, further distinctions different climatological, geographical, are currently made between the world of edaphic, orological, biotic or sociological plants (plant ecology), animals (animal conditions. Even a difference in one of ecology) and man (human ecology). A the natural characteristics of a given particular aspect of human ecology is natural ecosystem, e.g., temperature, further known as health ecology, defined light, precipitation or altitude, resulted by Zielhuis (2) as "The study of the in the failure of non-indigenous cultures, processes which at the level of biotic especially when the life form in question and social relations between man and had little if any power to adapt itself. his environment are relevant to the Many instances can be quoted in this health, diseases and health care of man connection, such as the consequences of as a species and as a group". The results transferring tropical cultures to our of these studies will help public author­ temperate zones. Conversely, natural ities to act with purpose and direction. cultures from our parts of the world Radioecology (also known as radiation appear to have difficulty in adapting to ecology) is that branch of ecology which tropical areas. The well-known dandelion deals both with the transfer of radio­ which flourishes in low-lying polder nuclides in the ecosystems in relation to areas cannot manage, phenotypically, the protection of man and animals i.e., in its physical form, to be more than against the direct hazards of radioactive a small, stunted plant in mountainous contamination and with the effects of areas. ionizing radiations on the biotic com­ ponents of ecosystems (3). There are a number of factors which determine the natural (5) ecosystem and In the natural physical habitat, with which are essential to man, plants and definite abiotic ecological characteristics, animals, system-linked environmental fac• also known as the biotope, a natural tors such as : community will be formed with a population having specific characteristics. - climatological factors : temperature, In 1877 Mobius gave the name of rainfall, vaporization, light, sunshine, biocoenosis to a community of all types wind; of organisms living permanently in the - edaphic factors : physical and chemical same biotope. This community is very composition of soil, air and water; the substrata in and on which man, plants and animals live; 1 Oikos = literally "dwelling place": the study of homes, habitats or households, a - orological factors : altitude; in general neologism related to classical "economics". a series of complex influences of pri-

74 Fig. 2 : A watercourse is regarded as polluted if the water in it is unsuitable for all the purposes for which it could be used in its natural state.

marily a climatological but also partly of an edaphic nature; - biotic factors : the influences of man, plants or animals on the ecosystem; - sociological factors : those determining social cohabitation, the organic com­ munity of man, plants or animals.

Environmental hygiene Environmental hygiene is concerned with the health of man and the safe­ guarding of that health with respect to the exogenous factors affecting man from the human environment or ecosystem. (Endogenous health factors determined by heredity or appearing later in life will not be considered here.) System-linked and foreign environmen• tal factors — The exogenous factors of interest in this connection are in partic­ ular those foreign to the ecosystem and furthermore xenobiotic, or foreign to the body. Ecosystem-linked media such as air, water and food are polluted, contami­ nated or otherwise influenced by mate­ rials foreign to the system which are added artificially or involuntarily to the natural ecosystem and can be injurious to the health of man and his environment. In principle all forms of environmental pollution or nuisance are inadmissible and anti-ecological. The Dutch Air Pollution Law states that : "In principle no one is entitled to disturb and spoil the biophysical environment in equilib­ rium with which man, plants and animals have originated and evolved and to which, as we are increasingly led to realize, they are attuned".

However, the term pollution is hard to define, either qualitatively or quanti­ tatively. The most obvious definition would appear to be that it is caused when chemical, physical or biological mate­ rials which are foreign to the system in

Fig. 3: A number of developments in modem society, e.g., energy production, have not been accompanied by a corresponding realization that they could have disastrous effects by disrupting the natural balance.

7^ 76 some way induce changes in the compo­ Dose-effect relationship — The task for other reasons of an economic nature, sition of an ecosystem. of the environmental hygienist is to study for example, to set tolerance levels with In a number of respects, for example, harmful exogenous influences and either a dose greater than nil. the definition of water pollution for­ restrict them to a minimum or eliminate There are many aspects to the ques­ mulated at a meeting of European their causes in order to protect human tions which must be asked and answered experts in Geneva in 1961 is open to health and the natural environment. in establishing tolerance levels and the criticism: "A watercourse is considered According to the World Health Organi­ like. Which materials are harmful to the to be polluted when the composition of zation's definition, the term "health" has system, what is the nature of the damage the water or condition in which it to be interpreted very broadly : "Health and at which dose will there be harm? exists is directly or indirectly changed is a condition of perfect physical, mental It is necessary to have information on by man in such a way as to render it and social well-being and not merely an the dose-effect relationship. But here, less well suited to all, or at least some absence of illness or infirmity". too, there are considerable gaps in our of the purposes for which it could be Theoretically speaking, it would be scientific knowledge. used in the natural state". easy to exclude from the human envi­ Effects may become apparent in the According to this definition then, the ronment all factors foreign to the system, short term but also in the long term, criterion for judging whether water if other considerations, e.g., of an e.g., in the case of exposure to relatively is polluted is whether or not it can be economic nature, did not have to be low doses; they may also have a clinical used. Moreover, the only causal agent taken into account. or a subclinical character. To what extent does man's adaptability play a part here considered is man, whereas various other We must note that rapid technological or even immunize him? circumstances may contribute to pollu­ development, industrialization, the in­ tion, such as floods, animal offal or crease in traffic, urbanization and energy People living in mountainous areas cadavers, minerals from toxic ore depos­ production have not been accompanied are exposed to a considerably larger its (e.g., deposits containing radium), by an awareness that disturbances of the dose of (cosmic) radiation than those in etc. natural equilibrium could lead to disas­ low-lying areas; people living on the Matters or energy foreign to the system trous consequences (6). monazite areas of Kerala, India or Terra Rossa in Brazil, which contain may be classified in various ways in the There is one exception to these nega­ elaboration of measures relative to highly radioactive minerals, are simi­ tive aspects of industrial progress, larly placed. This radiation dose does not environmental hygiene. The following namely, the peaceful use of atomic categories may be distinguished : seem to have any influence on the energy. Development in this field is health or life expectation of the local - waste materials : as gases, fluids or surrounded by the strictest of provisions population. solids. This heading includes xeno­ on health protection and environmental biotica with the most widely differing hygiene. These standards are so severe Must tolerance levels be based on the physical and chemical properties, that it has taken a long time to get weakest link in the chain or should the including radioactive substances; this source of energy developed on a population average be taken as the 2 - residues such as pesticides and fertil­ commercial and competitive basis. reference level ? In terms of environmental hygiene the izers; One of the great problems confronting following objectives must be pursued - viruses such as bacteria and other environmental hygienists is to determine in order to protect man and his envi­ micro-organisms which may find a the maximum admissible levels of matter ronment : good nutrient medium in slaughter foreign to the environment. Russian houses and municipal garbage disposal hygienists set their standards in accor­ - a reduction in the concentration of plants; dance with the following principle : pollutants and particularly of the most - additives used as dyes, preservatives, "Any stimulus, whether pleasant or dangerous; antioxidants, emulsifiers, stabilizers, unpleasant, and of whatever kind, - the improvement of knowledge about antibiotics, hormones, etc., in the becomes unpleasant, intolerable and the dissemination and effects of manufacture and processing of food­ even pathogenic once it is inescapable". pollutants; stuffs ; It is well-known that for system-linked - the establishing of criteria giving the - thermal loading of surface or ground environmental factors there is also an dose/effect relationships; water by industrial cooling water; optimum dose situated between a given - the translation of selected criteria into - stench and fetid odours: industry; maximum and a given minimum and legal provisions or regulations. - noise: industry, means of transport; which, if exceeded in either direction, The criteria to be established could - ionizing radiations: industry, etc. produces a harmful effect instead of a take into account the following: useful one. For even an excessive use of cooking salt is harmful. As early as the - for man sixteenth century the Swiss alchemist - increased mortality rate Paracelsus observed that "Sola dosis - increase in number of hospital cases facit venenum" (it is only the dose which Fig. 4: Harmful substances can enter li\ing poisons). The optimum dose for mate­ organisms by a large variety of ways, e.g., rials foreign to the system is naturally - A much-used unit in animal experiments through drinking water, as in the case of these in this context is LD.™, i.e., the lethal dose cows. nil. It may also be desirable or necessary for 50% of the animals tested.

77 ­ increased number of cases involving In order to provide this information diseases of the respiratory organs it is necessary first of all, in analysing and lungs (e.g., bronchitis) a system, to define the relevant health, ­ absences from work ecological and epidemiological para­ meters, to observe, measure and examine ­ irritation of certain sensory organs at fixed recurring intervals over long (ears, nose, eyes, etc.) periods of time, to collect and analyse ­ for his environment information and then to establish appro­ priate actions. The problems having ­ damage to flora and fauna very many aspects require a multidis­ ­ reduced sunlight ciplinary approach. The research must ­ reduced clearness of surface water have at the same time a fundamental, ­ damaging effect on materials and an applied scientific and an operational buildings (corrosion) character. ­ degree of eutrophication of surface Transfer pathways (7) — In assessing water. the degree of risk of waste disposal for human health, the following factors have Ecological research in general to be examined: ­ the processes whereby the final link The character of ecological research in food chains, air or water is polluted; is determined in the first instance by the ­ the processes of transfer or agents to point of view from which it is to be conducted, e.g., that of man, plants or and within man, including metabolic animals, and then by defining the behaviour; research objectives within the appro­ ­ the epidemiological aspects of the priate category. The choice of the para­ nuisance. meters to be studied and relevant to the The transfer to man of system­foreign ecosystem depends first and foremost on agents may occur directly, via air and this. However, it should not be forgotten drinking water. In this case the number in the analysis of the system that the of factors and transfer processes which ecosystem forms an absolute unity. influence physicochemical changes in Furthermore one should not forget the agents and their concentration and interaction of the biocoenose with the dilution is relatively small. They are physical habitat and the state of its restricted chiefly to dilution or diffusion delicate natural balance. by air currents or by water discharge. Air and drinking water are thus the last Ecological research concerned with link. man has many aspects, e.g., with regard to his behaviour as a living species in The food chain, however, is an the midst of other living organisms in a indirect pathway with numerous links. given ecosystem; as a causality factor in For once system­foreign agents (see the changing and planning of the bio­ Fig. 5) are introduced into the food chain sphere and not least with regard to the through the air (by atmospheric precip­ consequences of such changes for man itation) or through water (by irrigation, as a species. for example), the transfer is influenced ■— at the various links or trophical levels — In view of the nature and extent of by a number of factors and processes the problems in this field, and our before the agents reach the final link relatively recent realization of them, in the food chain (vegetable or animal it goes almost without saying that our consumption products). Physiological, knowledge is far from complete and metabolic and other processes in plants, that a lot more research is needed. animals and hydrobiotics can cause concentration, dilution and change in Many questions need to be answered the physicochemical characteristics of in the short run, such as the dose­effect agents. Rainfall can cause erosion of the relation of a very large number of pol­ upper soil stratum. lutants and nuisances, the short and long term effects of exposure to often rela­ Food chains can again be divided into tively low concentrations or doses, the short and long chains. In the former case results of the interaction or synergisms soil and cattle are not included as inter­ of environmental nuisances, the behav­ mediate stages and contamination of iour of pollutants in the environment, plants for consumption, e.g., greenstuffs, the transfer mechanisms, etc. occurs directly. In the case of the so­

78 ;alled long food chains the stages soil ways, namely, air, water or food chain Fig. 5: System-foreign agents can enter the and cattle are present. and, in the food chain, the nature and human organism directly ( via air and water), but also indirectly (via one of the food chains ). From the practical viewpoint of quantity of the products consumed. health protection this difference between The metabolic characteristics of the direct and indirect pathways and short critical agent must be determined, as and long food chains is of great signif­ well as the critical organ in the human ment modelling. A system is analysed icance. For this determines not only body which may be exposed to this agent and the factors of transfer between two the method but also the extent of trans­ and thus to the greatest risk. links of the system are determined from fer and its importance is thus both which can be derived the concentration qualitative and quantitative. In the case It should be pointed out that the term ratio of a particular agent in two consec­ of radioactive contamination, the half- "critical" in this connection does not in utive compartments of links of the life or radionuclides is of great impor­ itself imply any danger; its sole meaning chain. These models also enable us to tance in this connection because of the is to qualify terms already defined in estimate the uptake capacity of a partic­ time lapse of the transfer. such a way that specific decisions on health protection can be taken as a ular ecosystem (hydrologicai basin, Assessment of the second series of result. atmospheric region) with regard to processes, those concerned with the system-foreign agents. By estimating transfer of agents foreign to the system The concepts, analyses, research and this uptake capacity — and account must to and within man, also requires com­ other aspects we have mentioned earlier also be taken of the environment's self- prehensive, systematic and multidisci- in connection with the transfer and cleaning capacities — we can determine plinary examination. The first stage may hazards of system-foreign agents as far the maximum quantity which can be be said to be the identification of the as the protection of human health is taken up into the ecosystem without persons or group of persons most exposed concerned can also be applied mutatis creating an unacceptable hazard for man to the potential source of the hazard, the mutandis to the protection of the other and his environment. This estimate must so-called critical group. This may be a components of the human and natural as far as possible allow for extra safety small population group (e.g., riparians environment. The objectives pursued may margins which may be introduced to who eat contamined fish from a river), a differ, but the principle of research and deal with new or as yet unknown pol­ part of the population (e.g., in the case supervision is the same. lutants, i.e., emission sources and system- of drinking water, etc.) or specific groups Uptake capacity - - Operational re­ foreign agents. Estimates of future devel­ of the population (children, young search may be considerably assisted by opments are essential here, and mathe­ people, etc.). In direct relation to this it the use of mathematical models, and in matical and similar models can again be useful aids. is necessary to identify the critical path• particular by the principle of compart-

79 Fig. 6: Impurities can be more dangerous when combined than in isolation; sulphur dioxide, for instance, is known to be more toxic in conjunction with particulates than alone.

80 Numerous parameters have to be effects of a somatic, mutagenous, carcin- Surveillance considered, such as the physicochemical ogenous, psychic or teratogenetic natu­ form of the agents, alterations during re. Account must also be taken here of If a strategy aimed at protecting man transfer, the manner and frequency of the nature of the reference group: is and his environment is to be effective, the discharge of pollutants (continuous it the entire population or a special it is necessary to carry out observational or discontinuous, high or low concen­ group of the population, a group of work (sampling and measuring) in order tration, controlled or uncontrolled as in patients already suffering from a partic­ to establish how things actually are at accidents, for example), the physical, ular disease, e.g., bronchitis, or, in the present and then to register changes and chemical and biological parameters of case of epidemiological research into possible future developments as and the receiving environment such as, for air pollution, a group of smokers or where they occur. example, flowrate, volume and tem­ non-smokers? This information and knowledge is perature of surface water, prevailing indispensable if suitable surveillance winds, frequency and quantities of A particular problem in this field is rainfall, soil composition, natural oxygen that of the synergism, or the effects of is to be exercised. Up to now measures and salt content of soil and water, nature the interaction of specific agents. This is were only taken once problems had and composition of local or regional the case, for example, with air pollution attained serious and obvious propor­ communities, etc. by sulphur dioxide and particulates. In tions, as was the case with the extensive general it is acknowledged that air pol­ pollution of surface water, air pollution This is simply a rough summary of the lution by sulphur dioxide in the presence in heavily industrialized areas and the factors confronting the ecological re­ of heavy concentrations of particulates problems of DDT, mercury, lead, etc. searcher in matters of environmental constitutes a greater danger to public hygiene. health than it does when no particulates Once parameters and transfer factors are present. This synergism has to be have been defined, the necessary means taken into consideration in evaluating the for systematic observation can be estab­ Epidemiological research general pollution of the environment and lished. The required sampling and the attendant hazards. Side by side with this ecological measuring stations have then to be set up. research there is also epidemiological In establishing protection standards research, concerned in this case with against ionizing radiations we are as it In the case of radioactive pollution the harmful or disease-inducing conse­ were "fortunate" in that the absorbed widespread observation networks have quences of environmental nuisance for radiation dose of the various radio­ been in existence now for over ten years the population in general. Progress in nuclides as such can be integrated with to measure pollution of air, rainfall, this field is considerably less advanced respect to the biological effect and can be water as well as foodstuffs and soils. than in that of non-human ecology. expressed in one radiation unit known as Quite a few complications arose, espe­ The field of industrial hygiene cur­ the "rem". In this way an evaluation of cially with regard to the sampling and rently provides a rich source of infor­ the harm commitment of all radiation measuring of food chains. Supervision mation, especially in toxicological mat­ sources can be given in a particular unit and control both of radioactivity in the ters, for the establishing of standards in of time. To date it has not yet been human environment and in the sur­ the field of environmental hygiene in possible to develop a similar integration roundings of nuclear installation plants general, although an essential difference unit for all environmental nuisances or has been organized for many years in a must be made between "voluntary" for certain non-nuclear groups or cate• satisfactory fashion, so that unexpected gories. hazards and those to which the popula­ situations in the field of radioactive tion is involuntarily exposed. It should be pointed out that a lot of contamination are now kept to a mini­ research conducted in the interests of mum. Epidemiological studies of fairly large health only shows significant and useful population groups are needed in order With the more conventional nuisances results when it is carried out in vivo or to estimate: we have a different situation. Although in situ. For this reason large-scale the problems are of longer standing, - the long term effects of environmental epidemiological research is extremely supervision and therefore observation nuisance, at both high and low concen­ important, although very costly and and measuring are in general still not trations and doses, and thus the harm­ time-consuming, if meaningful conclu­ entirely satisfactory. ful effects of living in a polluted area sions are to be reached. The results for many years; obtained from experiments on animals The reason for this is not only that - the shorter term effects of exposure to or using laboratory aquariums often have interest in these problems is much more different pollution levels for a number only a relative significance for extra­ recent, but also that the problems them­ of weeks or months; polation to man and natural circum­ selves are noticeably more complicated stances. Often they give only rough indica­ because of the greater variety of agents: - short term effects, e.g., of 24 hours tions which, in a number of cases, can every substance has its own chemical and exposure to high concentrations or be used as references for lack of better physical properties. Whilst the number levels. information. Such research methods may of specific nuclides examined in the This research may be designed to be quite helpful for a time, but they are nuclear field is very limited, the variety determine the lethal or disease-inducing certainly no panacea. existing in the non-nuclear field is very

¡I Fig. 7: // is barely credible that such a polluted piece of water could contain enough oxygen to enable aerobic micro-organisms to exist, but these play an extremely important part in the entire ecology of water.

S 2 great, as is the number of emission In view of the nature of the problems as sources also. Furthermore, the nature a whole and the research, etc., involved, and thus the presence of a certain pollu­ it is quite evident that multidisciplinary tant are not always known. When the cooperation on a large scale and above Rhine was polluted by the pesticide all at international level is of great endosulfane in 1969, it was more or less importance in the battle against envi­ only chance and the skill of the investi­ ronmental pollution to all parties who gating analyst which enabled the labo­ can, among other things, keep the costs ratory in question to identify the pollu­ involved to a minimum by exchanging tant, thereby averting a great disastre. information. Economic factors involved in the trade within the Common Market Each element or chemical compound also play an extremely important part requires an analytical technique of its here. own which, particularly in the case of trace elements, is often difficult. No less In many fields cooperation of this problematical is the question of sampling, kind already exists, but the actual needs because of the large number of emission and the possibilities too are very much sources. In this case a number of points greater. have to be established: the place where This international cooperation at the the sample is taken (altitude and distance same time places us under an obligation from the source), the density of the to harmonize our international termi­ network, frequency of sampling, alarm nology. In this field there is still a lot levels if appropriate, the evaluation of of work to be done. Only too often it is the pollution of the background, etc. apparent that experts of different nation­ This field also affords a wide range of alities fail to understand or actually research topics which in turn entails very misunderstand each other over a fami­ considerable investment of manpower liar technical idiom. Standardization of and capital (personnel, equipment, labo­ linguistic usage and techniques is indis­ ratories, etc.) for the research described pensable to international cooperation in earlier. applied science.

EUSPA 12-10 Conclusion

The ideal situation, where all environ­ Since this article was written, the Commis­ mental nuisances are eliminated, is, of sion of the European Communities has course, only wishful thinking. This submitted an action programme for environ­ would at the moment be too demanding, mental protection to the Council of Minis­ barely rational and in economic terms ters, which was approved in its great lines impossible. One criterion, or rather at in July 1973 (ed.). this stage an indication, has been suggested in this connection, namely the cost/benefit ratio; increasing efforts are Bibliography: (1) F. HAECKEL: "Ueber being made to analyse and balance the Entwicklungsgang und Aufgabe der Zoo­ logie" Jenaischer Z. für Naturwiss., 5 (1869), two elements of this ratio. The difficulties p. 353-370. (2) R.L. ZIELHUIS: "Gezond- involved in calculating the elements of heidsecologie" Tijdschr. Soc. Geneesk., 49 this ratio, and expecially in determining (1971), p. 90. (3) E.P. ODUM: "Consider­ the benefit factor, are numerous. How ation of the total environment in power high should we put the benefit of a reactor waste disposal" Proc. Intern. Conf. on the Peaceful Uses of Atomic Energy, 13 number of values which are hard to (1957), p. 350-353. (4) A.G. TANSLEY: estimate? It is easier to express absence "Practical Plant Ecology", Methuen, Lon­ from work for the working population don, 1923; see also: E. WARMING: "Eco­ in economic terms than it is, for example, logy of Plants", Oxford, 1909 and G.G. POLIKARPOV: "Radioecology of aquatic to express the incidence of sickness organisms", Amsterdam, 1966. (5) J.G. among the non-working population. In SMEETS: "Een vergelijkend ecologisch the latter case, for example, hospital­ onderzoek in opstanden van Queráis borealis ization could be used as a standard of Michx. F. en Queráis robur L.", (1957) reference. But this is only relatively thesis, Ministry of Agriculture of the Nether­ lands. (6) J.G. SMEETS: "Milieuveront­ realistic. The number of "invisible reiniging uit een internationale gezichtshoek" references" which cannot easily be Natuur en Techniek, 39 (1971), p. 393-404. measured or not measured at all is very (7) J.G. SMEETS: "Radioactieve besmetting high. van voedingsmiddelen" Voeding, 2 (1961), p. 62-70.

83 — 2001 : Remote control tongs for Performance characteristics operations under vacuum conditions Angle of travel 22°30 These tongs are designed for relatively Load capacity 3 kg The Commission's technical complex handling operations inside vac­ Clear opening 80 mm notes give descriptions of orig­ uum chambers with a leak rate of less inal results obtained under the than 1 · I0~7 torr. 1/sec. Euratom research programmes. — 2002 : Storage and handling apparatus Their purpose is to enable firms Vacuum tightness between the guide for material in rod form to decide whether they should tube and the push-pull rod, i.e., the Storage premises and labour for consider industrialising these system transmitting the gripping motion materials handling are generally consid­ results. to the tongs is assured by a removable unit located on the part of the tongs ered as a debit in the operating balance On the basis of article 12 of outside the vacuum chamber. sheet of an enterprise, as are production the Euratom Treaty, a non-ex­ delays caused by the difficulties of find­ clusive licence may be granted Leak-tightness between the guide tube, ing, identifying and handling the on the results covered by pa­ ball-joint and the wall of the vacuum required goods. tents, in so far as the licensee chamber is ensured by using a ball-joint This proposed storage and handling is in a position to make effect­ penetration of the vacuum-retaining system reduces the disadvantages men­ ive use of these results. The Retzloff joint type. tioned above to a minimum. conditions of the licence, as well as the royalties for tech­ Applications 1. A rack enables different types and sizes of rods to be stored in several nical assistance, will, for each Handling operations inside leak-tight horizontal layers; this arrangement individual case, be fixed after vacuum chambers or pressure chambers makes for : joint consultation. are extremely difficult. The use of tongs - a great reduction in the floor area Requests for additional inform­ of this type, which are very robust, necessary for storage, ation should be sent to: Com­ provides a simple solution to a large mission of the European Com­ number of problems. They can be used - easy identification of goods, munities, D.G. XIII-A, 29, rue in connection with metallurgy, electron- - very easy handling. Aldringen, Luxembourg. beam welding, in metalplating and heat 2. The design of this machine, which treatment, in space simulation, etc. is a grab which can place goods on

84 and the mounting (8) of the quartz tube. The chamber can be locked down by means of a lever (7) to permit operation with a slight over­ pressure. B. The mobile chamber mounting (8) and its guide pillar. This mounting is water-cooled to prevent overheating of the seals, and is attached to a carriage with a vertical travel along a pillar (9). The field coil (10) is also fixed onto the mounting. A heat shield (11) protects the pillar against the heat radiated by the crucible. The assembly is counterweighted for easier opening of the furnace, which can be done with a finger. C. 77;^ quartz chamber. Set on the above mentioned mounting, it consists of a transparent quartz tube with a hemi­ spherical upper end. No grinding is necessary, as the sealing surface is on the cylindrical portion of the tube. A jacket (12) in sheet aluminium is provided on the upper section in order to reduce losses due to radiation this type of rack and take them off and (5) can be used to set up a gas and also serves as a mounting for a again, and also perform all everyday circulation system inside the quartz prism to deflect infra-red rays emitted handling operations (placing on and chamber. Thermocouples can also be by the crucible, thus enabling the lifting from conveyors, vehicles, etc.) routed through the central hole to temperature to be measured by an ensures maximum safety in handling monitor the temperature at the centre optical pyrometer. operations. of the crucible. A crucible-holder (6) in the form of a ceramic tube is placed The unit enables an unskilled operator Advantages: in this central hole. A circular groove to store or remove the required material The advantages of this furnace lie in allows for the cooling of the base­ quickly and correctly. In addition, the its simplicity of construction and the plate. An O-ring housed in the base intrinsic features of this storage system ease with which it can be adapted to plate to provide a seal between it allow storage and removal operations other sizes of furnace. Simple design to be completely automated. solutions were found: 1. For leak-tightness; using the cylin­ — 2003 : An easily operated, all-purpose drical portion of the tube with no induction furnace for laboratory use need for grinding. 2. For the pillar and the locating system, This laboratory induction furnace was of which there are two versions accord­ designed for the extraction of fission gas ing to the weight of the furnace. The from nuclear fuels, a process carried out locating system is free from play and at a temperature of approximately 1400 offers very low resistance to move­ °C. In view of the original necessity for ment. that process to be carried out in a lead 3. Since the furnace is counter-weighted, cell, using a single pair of ball-jointed it can easily be worked manually tongs, the entire handling procedure was (without lifting apparatus), even in simplified as much as possible; potential the case of large units. The furnace operators can now take advantage of can be operated with just one finger. this for all metal-working processes, such as melting, sintering, annealing, metal- plating, or operations in special atmo­ — 2004: Metal gasket spheres. Few gaskets can withstand tempera­ This furnace is made up of: tures higher than 300 °C. A. The fixed base plate (1). This has a The Ispra Euratom Research Centre central passage (2) for connection to has studied this problem and has now the vacuum. A mounting, with a produced a metal gasket MET X with central hole (3) and offset holes (4) very good sealing properties.

85 77íe Joint Research Centre, Ispra electrodes gives, at equilibrium, a direct These high temperature thermocouples Establishment, of the Commission of the measurement of the neutron flux inten­ can be made in lengths of up to several European Communities has patented it sity. metres, and can be either rigid or flexible. and licenced two companies, Dilo and Neutron flux measurement is thus Manufacture, assembly and full technical Le Joint Français to mass produce and reduced to a simple and normal measure­ service are offered, including the follow­ market this product. ment of electron current by measuring ing tests: physical measurements insula­ the difference in potential at the contacts tion resistance measurements, helium of a load resistor. leakage test, X­Rays. Other special The emitter (central electrode) is tests can be carried out on request. generally made of rhodium silver or vanadium of known nuclear properties. CR/AL A feature of the Eurotronik is that they Ζ CR/AL can be manufactured in any length up to several metres (3). Ο Θ They can be supplied in rigid or flexible form. Quality control is carried This product is sold by the firm out on the product by means of the Franco CORRADI, Casella Postale 98, following tests: continuity, insulation 20017 RHO, Milano (Italy) ­ Tel: size, sealing and X­rays. Other special 930.29.55. tests can be carried out on request. Agent for the United States: LEICO Eurotroniks were developed at the INDUSTRIES Inc., 250 West 57th Ispra Joint Research Centre (Varese). Street, New York, N.Y. 10019 ­ Tel (212) 765­5290.

— 2007: Viscosimeter The instrument shown, as an example of the type, was developed for the ' ' ' X purpose of measuring viscosity under Θ Θ Θ neutron irradiation in a reactor. It is suitable for general use, however, in They are sold by the firm Franco particular to measure the viscosity of CORRADI, Casella Postale 98, 20017 fluids under high pressure, and of Some characteristics of the MET X RHO, Milano (Italy), Tel. 930.29.55. substances that for safety reasons must Agent in the United States: LEICO Solid, circular metal gasket, quadri­ be kept in closed containers. INDUSTRIES, Inc., 250 West 57th lobal in section. The temperature range goes up to Street, New York, N.Y. 10019 ­ Tel. 300 °C. The model shown covers a Made of Inconel 600 or any other steel (212) 765­5290. considered adequate for the proposed viscosity range of 0.09­2 centipoise. The use. range can be extended upwards or — 2006: Composite thermocouple Temperature range: downwards by I minor modification. minimum: cryogenic temperatures These thermocouples, which have been The apparatus makes use of the power maximum: 850 C. specially designed for measuring high transmitted by a liquid film of fluid Operating pressure range: ultra­high temperatures even where ionizing radia­ between two concentric cylinders oscil­ vacuum to 400 bars tion is present, have been developed at lating in opposite directions. Design Liquids: all liquids the ispra Joint Research Centre. They Features are illustrated in the accompa­ consist of a well insulated junction box nying section and block diagram. The Requires 3 to 4 times less compression (cold joint) (2) between the high tem­ receptacle (2) is suspended on two sets than any other known metal gasket. perature section (1) and the low tempera­ of springs (3) and from the outer casing ture section (3). (1). The receptacle is free to oscillate — 2005: EUROTRONIK — Self­powered The low temperature section is made along the axis of the outer casing. A neutron flux detector for in­pile continuous of the following materials: combination of coil springs (5) and flat neutron measurement, at temperatures up Sheath: stainless steel, Inconel springs (3) ensures that only axial oscil­ to 500 C Wires: 2 in Chromel, 2 in Alumel lations can occur. Eurotroniks work on the following Insulation: MgO Oscillations are induced by the electro­ principle: if two electrodes (1 and 2), The high temperature section is made magnet (8). The plate capacitors (6) and insulated from each other, are exposed of the following materials: (7) serve as transducers, modulating the to a thermal neutron flux an activating Sheath: Ta, Nb, WRe, Mo frequency of a high­frequency oscillator effect β will be generated mainly in the Wires: Pt­Pt/Rh, Pt/0.1 Mo, Pt/0.5 Mo, circuit. Demodulation produces a signal central electrode (the emitter). The W­WRe, Mo­Nb proportional to the amplitude of oscil­ resultant electron flux between the two lation which is recorded.

86 A float (4) is suspended in the recep­ tacle by another set of flat springs. Here again the type of suspension used ensures that the relative motion of receptacle (2) and float (4) is purely axial. The fluid under investigation is poured into the receptacle (2) until the float (4) is completely covered while leaving room for thermal expansion. The oscillation of the float in opposition to the recep­ tacle exerts a frictional force on the film of fluid between them, which damps the oscillations of the container, and the degree of damping is a measure of the fluid's viscosity.

1. Vibrometer 2. L.F. dual beam oscilloscope 3. Level recorder 4. Frequency counter 5. Temperature recorder 6. L.F. amplifier 7. L.F. oscillator

(Patent No. 59 527 Luxembourg)

— 2008: Quartz glass shield windows

Shield windows of quartz glass (e.g. Suprasil) display the excellent optical properties of that material. They also exhibit extreme leaktightness and resis­ tance to prolonged exposure to high temperatures owing to a glass-to-metal bonding process developed at the Joint Research Centre, Ispra. Their leak rate is generally less than I0~9 atm. cm3/s. in a helium atmosphere at 20 °C with an external pressure of 26 bars. They retain the same leak-tightness during prolonged (Patent No. 58 532 Luxembourg exposures to a temperature of 450 °C. 29.7.1969 Shield windows of this type are now in Schneiders A. und G. Hollebeck, EUR production on an industrial scale and 4817). can be supplied in several diameters ranging up to 150 mm. Flat spring For further information and conditions Designed for usein the viscosimeter, the of sale, please contact the Commission spring permits only movements vertical to its own plane. With the dimensions of of the European Communities' licensee: the example shown, the restoring force Société de Verrerie et Thermométrie is proportional to the amplitude when 135, rue du Théâtre the deflections are less than 2 mm. Paris 15e (France) Tel. 734-85-45

87 Recent publications on industrial chemical analysis methods

Eurisotop Information Booklets Eurisotop Technical Information (ITE-Reports) 18 d, n Special methods of measuring in activation analysis (monograph). 11 e High precision neutron activation analysis of 57 e Determination of oxygen, silicon, phosphorus manganese in pyrolusite and ferromanganese and copper in iron and steel by 14 MeV with the aid of an isotopie neutron source. neutron activation analysis (monograph). 61 f Activation analysis of Si and Al in bauxites. 59 d, f The technological and economic importance of the determination of oxygen in non-ferrous 62 d, f, i, n Non-destructive analysis of medieval gold metals (monograph). coins. 65 e 14 MeV neutron activation analysis (annotated 63 d, f, i, n Neutron activation analysis of Au, Ir, Cu and bibliography). Μη traces in platinum and rhodiated platinum wirenettings. 68 e Determination of oxygen in non-ferrous metals by 14 MeV neutron activation analysis 64 d, f Study of problems of chemical analysis of (monograph). noble metals. 71 d, f, e Chemical methods for the determination of 65 d, f, i, n Study of the assay of gas-contents in noble oxygen in non-ferrous metals (monograph). metal coatings. Nuclear analysis techniques in the production 72 d 66 e Nuclear analytical methods in the production and industrial use of noble metals (proceed­ and industrial use of noble metals. ings). Activation analysis with gamma-photons and 67 d, f, i, n Application of coincidence gamma-spectro- 74 f, e charged particles for the determination of metry for the assay of sub-micro traces of oxygen in non-ferrous metals (monograph). noble metals. Determination of carbon and nitrogen in 68 e Industrial uses of neutron activation analysis. 87 d silicon and germanium (monograph). 69 d, f, i, n Charged particles and gamma photon activ­ ation analysis in the noble metals industry (Ru, Rh, Pd, Ag, Os, Ir, Pt, Au).

70 f Application possibilities of radioisotope X-ray fluorescence in the noble metals industry.

71 e Stable isotope dilution: a possible tool for the analytical chemistry of noble metals.

72 d, f, i, n Trace analyses in Au and Pt using spark source mass spectrometry.

These publications can be obtained, free of charge, at 76 d, f, e The influence of the surface treatment of Commission of the European Communities samples on oxygen assays in non-ferrous D.G. Ill — Eurisotop Office metals. 200, rue de la Loi 77 d, f Comparative study of the methods of oxygen Β-1040 Brussels (Belgium) assay in lead-antimony.

(d = German; f = French; i = Italian; n = Dutch; e = English). SHOULD YOU WISH TO RE­ I wish to subscribe to the English/ ORDER FORM CEIVE euro-spectra REGU­ edition* of euro-spectra for one year LARLY, PLEASE SEND YOUR ORDER FORM TO: at the price of £ 2.00 ; US $ 5.00 Agence et Messageries de la Presse Rue de la petite Tie, 1 as from. 1070 Brussels, Belgium (Postal account C.C.P. 416.69) Name

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