Some Aspects of t h e Design of Radiochemical Laboratories HIOIVRI A. LI«:VY, M o n s a n t o Chemical Co. C l i n t o n L a b o r a t o r i e s , O a k Ridge, T e r m . L a b o r a t o r y facilities for r a d i o c h e m i c a l r e s e a r c h a r c classified a c c o r d i n g t o t h e level o f r a d i o a c t i v i t y i n v o l v e d i n t h e o p e r a t i o n s — microcurie, millicurie, a n d mullicurie. Problems often require m a n i p u l a t i o n s a t m o r e t h a n o n e of t h e s e l e v e l s a n d s e p a r a t e f a c i l i t i e s for w o r k a t m o r e t h a n o n e level m a y h e n e e d e d i n a s i n g l e l a b o r a t o r y . Ordinary chemical facilities a r e s a l i s f a e l o r v for w o r k a t Ibe m i c r o c u r i e level. S h i e l d i n g is n e e d e d b e t w e e n t h e o p e r a t o r a n d e q u i p m e n t , necessitating t h e c o n s t r u c t i o n of t h e specially d e signed hoods for work at t h e millicurie level, while m a n i p u l a t i o n s at t h e m u l l i c u r i e level m u s t b e c o m p l e t e l y r e m o t e l y c o n t r o l l e d a n d carried o u t behind heavy, ]>ermaiienl shielding.
in quantities far less than can stable elem e n t s . T h u s a beta-ray e m i t t i n g species can easily be quantitatively e s t i m a t e d in q u a n t i t i e s of t h e order of 10~° c u r i e ; for a radio-element having a half-life of 1 d a y t h i s corresponds t o only 4.5 X 10G a t o m s . (1 curie is the q u a n t i t y of r a d i o a c t i v e m a terial having t h e same disintegration rate a s 1 gram of radium—namely, 3.68 X 10 l ° disintegrations per second.) A few examples will illustrate some of t h e m a n y ways i n which t r a c o r elements can be applied to chemical problems.
XTLMOXC. the results of the impact of t h e M a n h a t t a n Project o n the field of chemistry, some of the m o s t far-reaching will derive from the availability of r a d i o isotopes of nearly all elements in q u a n t i t i e s h i t h e r t o unachievable. Radioisotopes will find immediate application in m a n y branches of fundamental a n d applied r e search and elsewhere in the chemical field in the role known a s "tracer". Further in the future, but definitely within t h e realm of possibility, is the use of massive quant i t ies of radioact ive material to induce new chemical reactions. Biological experimentation and medical therapy h a v e found important uses for radioisotopes and these can be expected t o multiply. Essentially there have been introduced two relatively new branches of chemistry —one dealing with the production of radioact ive species a n d one relating to t h e i r application to chemical, biological, m e d i cal, a n d technological purposes. T h e s e branches bring new techniques and p r o b lems, and so necessarily new sorts of i n struments, equipment, a n d facilities t o t h e chemical laboratory. It is t h e purpose of this paper to explore t h e requirements of a chemical research laboratory which is t o make full ut ilizat ion of these news tools.
1. Properties of m a t t e r in extremely dilute states: t h e solubility of b a r i u m sulfate in water coidd be directly determined b y equilibrating with its s a t u r a t e d solution a portion of this salt in w h i c h some 12.8d Ba 140 is incorporated a n d estimating t h e minute concentrations of dissolved barium b y means of its radioactivity. 2. Identification and estimation of competing reactions: Suppose a s t u d y is being made of t h e bromination of benzene t o give t h e m o n r ^ r o m o derivative a n d an estimate is desired of the e x t e n t t o which t h e various dibromobenzenes a r c formed. T o the reagent bromine a known activity of radiobromine is added. To a small portion of t h e crude reaction product, known quantities of t h e three dibromo compounds a r e a d d e d a n d from t h e mixture a portion of each is subsequently recovered in as pure a condition as possible, b u t not necessarily quantitative. E a c h recovered sample is then weighed a n d i t s radioactivity measured, yielding d a t a from which t h e distribution of reagent bromine among t h e several compounds is a t once calculable. 3. New analytical p r o c e d u r e s . Sodium could be estimated as follows: To t h e unknown aqueous s a m p l e a known activity of 14.8 hour N a 2 4 is added. Sodium chloride is then precipitated in a pure state by means of hydrogen chloride gas, t h e solid separated, washed, dried, a n d weighed, a n d its radioactivity is determined. Although t h e separation will not be quantitative, the fraction of the original sodium recovered is given by the ratio of final to initial activities, a n d s o t h e correct assay established.
Background The usefulness of radioisotopes to t h e chemist and biologist for the most p a r t arises from two fundamental characteristics: 1. Being isotopic with ordinary chemical elements, a radioelemcnt behaves chemically inmost respects exactly a s docs t h e same element composed of ordinary stable isotopes in t h e same chemical s t a t e . [Some exceptions to this statement are k n o w n : (a) Radioisotopes usualty have a t o m i c weights a n d m a y have nuclear spins different from those of their stable counterparts, leading sometimes t o relatively minute differences i n chemical be-, h a v i o r ; effects of this sort have been m a d e the basis for separating stable iso-
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topes of hydrogen, lithium,, a n d nitrogen by chemical exchange. (6) At t h e instant of radioactive decay a recoiling atom is endowed with a high degree of kinetic energy and is thus in a highh' reactive s t a t e ; this phenomenon, known as the Szilard-Chalmers reaction, has also been used to effect separations of isotopes. ] At the same time, their radiation provides a method of distinguishing two or more " k i n d s " of a t o m s of the same element and properly used enables a n investigator to follow t h e course of an element through a chemical reaction or series of reactions. 2. B y means of their radiation radioelements can be detected and estimated I.
About
the jiwtthor
TI
H EXTti A. LEVY, born Sept. 12, 1913, I in Ocnard, Calif., received his under- I graduate education in t h a t state, at- I tending t h e Oxnard Union High School I and t h e California Institute of Tech- I nology. After obtaining his B.S. degree I | in chemistry in 1935, he stayed on with I t h e institute and completed Ids work I for t h e P h . D . in t h e field of structural II J chemistry in 1938. I I Upon finishing his graduate studies I [ h e remained with t h e institute and. I ! continued his research work in t h e I I field of chemistry. This experience I I gained for him a broad background I i which served him well when he later 1 || joined the M a n h a t t a n Project. !| | After a one-month indoctrination J ; period at the Metallurgical Laboratory, !| | he came t o t h e then newly-organized il Clinton Laboratories in September | 1943, where h e has played an important I ! role in the development of radiochemi- I cal techniques. H e has m a d e m a n y valuable contributions in this relatively new branch of chemistry, n o t only in connection with t h e design of new facilities, b u t also in the carrying out of fundamental and applied research.
CH E M l C A L
Hazards The same characteristics -which make radioactive materials so powerful a tool to research and development also render them among t h e most hazardous encountered by the chemist. All of t h e notorious hazards of the radium i n d u s t r y will be associated with t h e use of these new substances, and furthermore m a y be magnified manyfold because of t h e v a s t l y larger quantities of pile-produced radioactivity available. Radioactive substances a r e dangerous in extremely m i n u t e quantities w h e n inhaled o r ingested, a n d in s o m e w h a t large quantities through t h e e x t e r n a l effects of
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their radiat ions. Toxicity varies from one isotope to another, depending among other factors o n t h e type of radiation emitted, t h e half-life1, t h e mode of metabolism of t h e element, and the rate a t which it i s eliminated from the body. T h e alpha-em liters of intermediate half-life (less than 10 5 years) are among t h e m o s t toxic. Of these plutonium constitutes a "horrible example" whose extreme toxicity is illustrated by the fact that t h e tolerance amount of the substance when fixed in t h e body tissues is only 0.5 microgram. Effects of external radiation may be either a c u t e , produced b y brief exposure to high i n t e n s i t y sources, or chronic, produced h y repeated exposure to relatively modest sources. T h e second of these is exceedingly insidious: repeated mild exposures m a y give no visible evidence of damage; yet years after exposures h a v e ceased exposed tissue may become cancerous. Biological experimentation b o t h within and outside t h e M a n h a t t a n Project has resulted in the adoption of a tolerance dosage of r a d i a t i o n believed to be safe even for indefinitely repeated exposure; this dosage i s 0.1 roentgen per day. T h e roentgen is defined a s t h a t q u a n t i t y of radiation which falling on dry a i r under standard conditions produced 1 esu of ion pairs per cubic c e n t i m e t e r . Excellent instruments are available for detecting, measuring, and recording intensity of radiation and exposure; with t h e i r use avoidance of overexposure is practical a n d convenient. General
Principles
The I m p o r t a n c e of t h e radiation hazard in radiochemistry depends on both the quantity of radioactive substance as m e a s ured b y disintegration rate, a n d on the quality of the radiations—whether alpha, beta, or g a m m a , and regardless of energy range. Since alpha-rays a r e very easily absorbed (by a few centimeters of air, or by the wall of any ordinary laboratory vessel) t h e external radiation hazard as-
O OOl A C
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-tracer
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y Tracer S u p p l y IO - 1 0 0 Experiments IO Mc - 5 ° 0 m c Scale of Operations i P r o d u c t i o n of Rodicisotc b mc — lOO c or mors
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Experimentation
Medical
Therapy
Z
Possible Future IndustTia' Rodiography 5 0 m c - C O O c or more
Fig. I. various
Chart showing problems
approximate
sociated w i t h a l p h a emitters is of little importance; consequently i t is conv e n i e n t t o discuss equipment and techniques a p p r o p r i a t e t o alpha-radiation separately from t h e corresponding r e q u i r e m e n t s for the more penetrating b e t a a n d gamma-rays. In dealing w i t h t h e l a t t e r it h a s been found useful to classify t e c h n i q u e s as appropriate for slightly active, moderately active, or highly active samples. W h e t h e r a given source should b e handled b y o n e or another of these techniques depends, in a d d i t i o n to i t s radioactive intensity, on t h e hardness of t h e r a d i a t i o n and on the complexity a n d duration of t h e operation t o he performed; nevertheless, facilities a n d techniques have been found t o fall naturally into t h e s e t h r e e categories whose division points can be roughly denned in t e r m s of radioactive intensity as follows: (a) the microcurie level, covering activities up to 1 millicurie, (b) t h e millicuric level, ranging from 1 t o about 500 millicuries, a n d (r) t h e m u l t i curie level, covering a c t i v i ties greater t h a n a b o u t 0.5 curie.
F i g . 2. Tongs commonly used in lovvlevel radioc h e m i c a I manipulation s 2 4,
•
—
for
It is a characteristic of radio-
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range1 oj radiouctivity
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chemical work that operations a t t h e higher levels always entail associated operations a t t h e lower levels. T h i s feature arises from t h e fact t h a t radiochemical m e a s u r e m e n t s a r e almost always m a d e on samples of t h e lowest level of radioactivity—5 X 10~ 10 to 5 microcuries. T h e p r e p a r a t i o n of a sample of t h i s size for measurement, or a n y other operation at a comparable level of radioactivity, is very easily s u b ject to accidental contamination if carried out close t o very active samples; consequently it is good practice to provide s e p a r a t e laboratories for operations a t different activity levels, a n d to t a k e u n ceasing care t h a t t h e low-level laboratory is not c o n t a m i n a t e d . I t is appropriate a t this point t o m a k e a s u r v e y of applications of radioelements i n order to gain a n idea of the level of r a d i o a c t i v i t y required for various t y p e s of problems. Such a survey is shown schematically i n Fig. 1. On this chart, the horizontal scale denotes the q u a n t i t y of radioactivity, ranging from 5 X 10~ 4 curie on the left to 1,000 curies on t h e right. A c t i v i t y ranges associated with typical operations a r e indicated b y t h e several oblong boxes. T h e heavy vertical lines div i d e t h e activity scale into t h e three categories mentioned above. I t should be emphasized t h a t t h e boundaries of various boxes are all more or less arbitrary and a r e to be t a k e n as typical illustrations only. Perhaps t h e most striking feature of the d i a g r a m is t h e large proportion of boxes in t h e lowest category of radioactivity. On t h e upper line t h e range of samples app r o p r i a t e for measurement w i t h . a GeigerMiiller counter is indicat ed. T h e separate boxes for b e t a a n d gamma samples a r e a consequence oi t h e fact t h a t measuring i n s t r u m e n t s are considerably less sensitive t o gamma- t h a n to beta-rays, necessitating 3169
larger s a i n p l o of tin* former. The box labeled "Experiment with Beta Tracer'* covers the range from 20 to 1,000 times t h e size of a counting sample. T h e next box, "Beta Tracer Supply for 10 to 100 E x p e r i m e n t s " , indicates the radioactivity which might be required for a n e x t e n d e d series of tracer experiments. T h e corresponding quantities for g a m m a - r a y e m i t t i n g radioisotopes come next. M u c h higher levels of activity a r e encountered in the preparation of radioisotopes than in their experimental use. A bombarded target from a cyclotron will usually fall in the intermediate millieurie range. Bombarded uranium from a chainr e a c t i n g pile can achieve activit ies of m a n y curies per kilogram a n d its processing req u i r e s elaborate techniques a p p r o p r i a t e t o these high activities. Sources for biological experimentation and medical thera p y usually lie between one microcurie and one curie a n d thus fall into both t h e lower a n d i n t e r m e d i a t e categories. F u t u r e developments m a y well bring n e e d for sources of heroic proportions; as an exa m p l e the field of industrial radiography m i g h t be mentioned, where sources of several thousand curies may prove useful. Beta
and
Gamma
Radiators
Microcurie R a n g e . Operations with b e t a and g a m m a e m i t t e r s at levels of r a d i o a c t i v i t y in the microcurie r a n g e are n o t usually very different from most ordin a r y chemical operations, and can for t h e m o s t p a r t be carried out in a n ordin a r y well-equipped lalMoratory. T o be sine, t h e r e are new, characteristic techniques peculiar t o radioehemistry e x p e r i m e n t a tion, b u t these are reflected for t h e most p a r t in minor rather than major i t e m s of equipment; similarly, serious health h a z a r d s are associated with radioactivities even a t this low level, but t h e y can b e circumvented without elaborate revisions in standard laboratory design. A n exception to t h i s s t a t e m e n t relates t o counting a n d o t h e r radiometric equipm e n t . Sensitive instruments of t h e sort required for precise radiochemical m e a s Below. chemical activity. ivaste.
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-licMilorictl -"- H E rapidly increasing use of radioactive materials in connection with investigations in the fields of medicine, biology, a n d agriculture necessitates the construction of laboratories incorp o r a t i n g special features and facilities for t h e protection of the personnel engaged in this type of work. T h e insidious nature of radioactive materials d i c t a t e s t h e necessity for providing facilities, t h e adequacy of which is based u p o n experience and well-planned designs. T h e M a n h a t t a n Project has been u n i q u e in t h a t so much of the -work h a d t o be done under the most u n u s u a l conditions because of the presence of intense radiations. *\Ve were forced to devise ways and m e a n s of coping with this treacherous h a z a r d in order t o provide safe working conditions. T h e r e are reasons to believe that many experimental investigations now under consideration in hospitals, educational a n d research institutions, and u r e m e n t s are best located i n a const antt e m p e r a t u r e room whose walls provide shielding against radiation from sources outside. T h e l a t t e r is especially desirable if work, with sources in t h e millieurie region or higher is in progress in the neighborhood. Counting rooms a t Clinton Laboratories are built with 2-foot-thick concrete walls, a n d h a v e air-conditioning equipm e n t t o hold t h e t e m p e r a t u r e dose t o 70° F . C a r e and vigilance are mressary to p r e v e n t c o n t a m i n a t i o n of counting rooms b y q u a n t i t i e s of radioactive materials too m i n u t e t o constitute a health hazard hut a m p l e to interfere with precise measurements. Other necessary i t e m s are a * 'contamin a t i o n counter", or suitable substitute, for checking u p o n the radiochemical cleanliness of glassware and other items, and a portable radiation meter for detecting d a n g e r o u s levels of radiation and ascert a i n i n g tolerance exposures. Best prac-
Fig. 3. An elevated, shielded hood Jar operations at intermediate levels of Right. Fig. 4. A sink Jor disposal of Note the knee-opera ted water valve
Comment&industrial laboratories are greatly handicapped, b y t h e lack of facilities a n d personnel who possess t h e technique and " k n o w - h o w " of handling d a n gerous quantities of radioactive m a t e rials. Any information and knowledge which may be passed on to those indiv i d u a l s who h a v e n o t been associated with the A t o m i c E n e r g y Project will ssurcly be in the best interest of scientific progress. The dissemination of this t y p e of information, gained t h e " h a r d w a y " , will prove t o be most valuable t o those who h a v e received training in special fields such as biology, medicine, chemistry, and physics, b u t who h a v e TIO knowledge of the necessary facilities required for carrying on work involving t h e use of radioisotopes. According to present plans, more d e tailed discussions pertaining to t h e rigid precautions for protection of personnel will he published in t h e near future. E D G A R J.
MURPHY
tice requires that all personnel working in t h e neighborhood of the laboratory 'wear pocket r a d i a t i o n meters which are read daily, and t h a t records of all exposures b e kept for future reference. R a d i o active contamination on the hands of personnel is a serious hazard a n d should b e checked frequently. Disposal of r a d i o active wastes on t h e microcurie level is usually n o t a difficult problem, since it is often permissible t o use ordinary d r a i n s ; however, the safety of this procedure should be investigated. W i t h respect to chemical manipulations, the chief r e q u i r e m e n t for safe operation i s that sources of even a few h u n d r e d t h s of a millieurie are never brought into close proximity with body tissues; this is ordinarily a v o i d e d w i t h o u t difficulty b y use of properly designed tongs a n d o t h e r m e chanical devices. Some are shown i n Fig. 2. Millieurie Level. Operations a t t h e
radioradioactive
CHEMICAL
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Left. Fig. 5. A precipitation vessel for remote control operations. Right. Fig. 6. A magnetically controlled distributions unit. Ifoth tlesigns by #>. G. Stang intermediate level of activity are characterized by the necessit\- for shielding between the source and t h e operator. Two distinct techniques have been developed; one constitutes "close" shielding around individual pieces of e q u i p m e n t a n d is applicable to t h e less penetrating radiations (beta a n d x-ray); t h e other comprises the use of general shielding a n d is necessary w h e n gamma radiation is encountered. T h e latter is of more general applicability a n d will b e discussed first. T h e general shielding method involves the erection of an absorbing wall between t h e operator a n d the a p p a r a t u s containing active material, manipulations being carried o u t with suitable devices over, around, or through the barrier.
An arrangement of this sort is illustrated in Fig. 3. T h e working volume is a spacious, well-lighted hood having walls and floor of lead 3 inches thick and lined with stainless steel sheet. T h e front wall, or barrier, of lead, is 6 inches thick. I t is convenient to erect the barrier t o a height of some 6 feet or more above floor level, so t h a t an operator standing on t h e floor is completely shielded from sources inside the hood. When performing manipulations, t h e operator stands upon a foot-high platform. General visibility is provided by a tilted mirror placed above a n d a t t h e back of t h e hood. The usual laboratory services are conveniently located a t the front of t h e barrier. T h e hood vents are of stainless steel and are so arranged t h a t fumes are withdrawn either close to the floor of the hood or close to its ceiling. A high-capacity fan is required. A chainfall traveling on a monorail above t h e hood permits heavy apparatus, such as a shipping shield, to be placed m. t h e hood. T h e depth of the hood—i.e., t h e distance from the floor of t h e hood t o t h e top of t h e barrier—should b e adapted to t h e nature of the apparatus to be installed; three depths of 1, 2, and 3 feet have been provided a t Clinton Laboratories. In the case of the deeper hoods, it is best t h a t part of the barrier be removable in order to facilitate installation of equipment. Detailed description of manifold remote control devices developed on t h e M a n h a t t a n Project is beyond the scope of this paper; however, b} r way of illustration, there are shown in Fig. 4 an all-glass device for carrying o u t precipitations and nitrations and in Fig. 5 one for directing a liquid stream in one of four possible paths. T h e former consists of a glass vessel formed from two Pyrex bottomless Erlenmeyer flasks which h a v e been sealed together; a t the b o t t o m of the ves-
sel- i.e., a t the nock of t h e lower flask— is sealed a porous glass disk. T h e region below the disk i s maintained under controlled pressure. When positive pressure is applied, the p o r o u s disk is impervious to liquids and t h e vessel serves as a beaker; when xiegativc p r e s s u r e is applied, it functions a s a filtering flask. The shape is chosen because it allows t h e walls t o be washer so of shielding is required a s with beta sources a t the millicxiric level, it is most convenient to build si heavy-walled jacket for each piece of equipment which contains active material. The region o u t s i d e the jacket is thus made safe radiation wise, and m a n y manipulations c a n b e carried out by relatively simple modifications of ordinary techniques, the chief difference being t h a t the hand of the operator must never be brouglit directly o v e r a n open vessel. The sliielding j a c k e t s may be of transparent pLastic, so t h a t visibility is n o t sacrificed. T h e special requirements of a laboratory i n which manipulations of this sort are carried out fire much l i k e those for the
lielotv. Fig. 7. A mixing cylinder for use with beta-radiating wnaterinls. Right. Fig. 8. An assembly for dispensing, diluting, and handling beta-active solutions. Ifoth courtesy of P. C Tompkins, A. liroido. and S. D. Teresi
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Figs* {) and 10. Tivo of storing rndionctiic
mctlio
