Semihot laboratories NELSON B. GARDEN University of California, Berkeley, Calif.
Analyzing the problems in radioactive work with ‘(1 curie level’’ leads to ambiguity, as this description leaves two uncertain factors in planning mechanical design. The degree of hazard depends upon the energy of radioactive radiation, and the weight or bulk of material involved could be very large or very small. A survey of the probable source of most radioactive materials makes it logical to expect gram quantities of material as a maximum, but micro quantities will be encountered most
frequently in laboratories, Because of these small quantities it appears possible to adopt a policy of constantly holding and transferring radioactive materials of practically every kind in closed containers or systems. Progress has been made in developing special chemical procedures and equipment to carry out this policy and, ac these become further improved, work in closed systems will be done with such facility that hazards will be eliminated and efficiency and accuracy will be increased.
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primarily serves as merely a new instrument. It is a detection instrument many times more sensitive than any other detection device we have known. With few exceptions the radioactive energy is not used as such but furnishes the final determination for any work after other data have been gathered-titration end points and pH determinations, along with evaporation, extraction, precipitation, and all ordinary chemical processes. At some time in the future radioactive molecules may be incorporated in chemical compounds and the activity used to influence the chemical bonds, but this again cannot be anticipated for the near future. So with the exception of the several physiological applications in medicine and the power pile (and the manufacture of a pure isotope, such as mercury from gold), the use of radioactivity is the quantitative or qualitative determination as the final step in a problem and invariably involves counting equipment.
ERlIHOT laboratory design is receiving considerable attention a t this time. “Semihot” is a designation which has become generally used, but in many cases those who use the title differ in their concept of what it means. It would seem advisable to clarify the matter somewhat. The design of laboratories and equipment for work with radioactive material is in an exceedingly elementary stage. Not only is radioactivity itself new, but the uses to which it will be put in the future are still very indefinite. The problems involved have little in common with previous developments and there is no precedent upon which to start new designs. Thus, without a good starting point and with vague ideas of the future application of radioactivity, it is not surprising that there has been hesitation to take rapid steps along the lines of laboratory design. The indications are that laboratories may become more elaborate and the designs more difficult as the scope for the use of radioactivity broadens. In undertaking the design of a semihot laboratory it is even more important than in most planning t o make a survey of the factors involved and to specify what will apply and also what will not apply. Revamping laboratories is time-consuming, very expensive, and probably unsatisfactory when completed. This statement is based upon first-hand knowledge acquired the hard way over the past two years. TYPE OF WORK
As the first factor, it is necessary to recognize what kind of work is t o be done-whether manufacturing and production, use and application of final products, or research and investigation. The manufacturing and production of radioactive material are obviously restricted to those few localities with piles or accelerators such as cyclotrons. At such points larger quantities of materials would probably be handled, justifying the design of special equipment and routine processes. Laboratories of this type are not considered here. The application of finished products also is not being considered a t the moment. An example of this is the use of 1131 or P32 in hospitals, where a purified or isotonic calibrated solution is re ceived by shipment and administered to patients without further processing. The laboratory being considered is one to perform chemical and general processing of radioactive material which can be shipped to it. The availability of this type of material is limited.
CHARACTERISTICS O F RADIATIONS
The third point to settle is the type or types of radioactivity that will be handled. Only the alpha-, beta-, and gamma-radiation are considered here, disregarding the possibility of neutrons that may be derived from radium, beryllium, or other sources and considering any x-rays together with the gamma radiations. It may be well to mention here the approximate range of 4 om. of air for alpha-particles, and the ease of shielding against them with thin rubber gloves or even the human skin, but some of them are very nasty from a health consideration if they get inside the body through the lungs, a cut, or the mouth. Alpha-emitters occur at the heavy end of the periodic table and much work has been and is being done with this type of radioactivity. The beta-particle travels a fairly short distance in air and can be stopped with rather simple shielding. It is energetically a dangerous radiation and can penetrate human tissue and do harm. The gamma, the most penetrating of the radiations, requires the elaborate shielding of lead, concrete, or other heavy material. All three types should be included in design, unless very special conditions exist. QUANTITY O F RADIOACTIVITY
The fourth point to consider is the quantity of activity necessary for the work. This we have stipulated as “semihot.” The quantity of activity is usually measured in curies, one curie being 3.7 X 1O‘O disintegrations per second, but this unit does not tell us whether i t is a ton of material or a submicroscopic amount, whether it requires inches of lead for shielding or practically nothing. It does not tell us the type of radiation, whether it is a point source or a solution, what the self-absorption is, what the energy or half-life of the radiation is. At least a rough estimate of these points should be available for design specifications in some
FUNCTION OF RADIOACTIVITY
The second point t o recognize is the function of radioactivity. T h e term has taken the popular fancy and has run away with the imagination, so that it is not generally realized that radioactivity
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INDUSTRIAL AND ENGINEERING CHEMISTRY
applications. Radioactivity's part is in counting, and practically a n y determination can be made by starting with 1 0 ' 0 counts per second, so that there will seldom be cases requiring more than 1 curie; if more is started with, an aliquot can be taken. Hence let us assume that a dedign for 1 curie of gamma-radiation of high energy will care for all cases. This means that several curies of lower energy activity can be handled in the same laboratory with the same equipment. HAZARDS IiVYOLVED
The fifth point is to analyze the hazards. In the early part of the work and during the war this consideration was limited to tho question of health. Much of the work was devoted to frantic exploration of virgin territories of isotopes and only rough indications of success were hoped for. So-called tolerance doses were determined by extrapolating from animal experiments and then allowing a generour factor of safety. Much has been written concerning this and the rules and regulations are well known. The splendid safety record speaks for itself. The problems undertaken recently and proposed for the future all require more and more exacting conditions, and technical contamination can ruin month3 of research work. For exampie, in looking for several counts per minute in the liver of a mouse, a few spurious counts can destroy the value of the work. This technical contamination is hundreds of times smaller than the levels for tolerance doses based on health consideration, so that if we design against the hazaid of technical contamination the health problem is more than amply provided for. METHODS O F OPERATION
The sixth pbint is the determination of a policy for dealing with radioactivity. &lost of the work has proceeded on the assumption that open handling of active mateiial can not be avoided and that contamination of air, se\%ers, benches, vialls, floor9, and workers' clothing niuat necesarily occur. Hon ever, bigger and better blowers, filters, decontamination pi ocedures, segiegation of aieas, and a multitude of monitoring instruments and personnel can maintain conditions so that work can be done with safety and a low general contamination. Another policy is to keep radioactivity completely confined at all times. The advantages of this phiIosophy itseIf can hardly be questioned, but the ability to employ it in practice is widely questioned. To achieve this in satisfactory measure is indeed a challenge to engineering ingenuity, both technical and psychological. Chemists must adopt a new psychological approach to the problems, but as radioactive chemical work is new with new problems, why is it not logical to expect them to adopt a new philosophy where a major problem is undertaken? Chemists must think in complete runs and prepare detailed flow sheets-much more detailed than are ordinarily thought of-and if alternate or substitute processes might be tried a t any point in the flow sheet, this also must be included. From these flow sheets the engineer prepares the setup of a closed system, employing remote control, special gadgets, proper materials, adequate shielding, etc. Cooperation between chemist and engineering specialist ensures an installation of superior safety and efficiency, and increases the probability of the success of the work. In any new complicated setup, dummy runs should be made, for it is impossible to take pieces out of the process once active work begins; these dummy runs prove of great help to those who are not accustomed to working Kith a time factor against them. Radioactive materials are constantly decaying, and especially with short-lived material delays cannot be tolerated. An efficient setup is a necessity. Once the special equipment is manufactured and the more elaborate setups ale made, the simple runs can make use of the same gadgets. A choice must be made between these two approaches to handling radioactivity
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PRINCIPLES OF DESIGN
Having adopted specific answers to the preceding six questions, one can proceed with some confidence to design a laboratory. If the policy of dilution, contamination, and decontamination is adopted, materials and laboratory design become of extreme iinportance. Excellent data have been prepared regarding this and are presented in other papers of this series. At the Radiation Laboratory in Berkeley sufficient progress has been made a.long the lines of keeping activity totally enclosed to encourage further developments. Under these condit,ions tho laboratory specifications for design, materials, equipment, ventilation, waste problems, etc., become simple and t,he solution t o problems is transferred to so-called gadgets or unusual engineering. The philosophy adopted in Berkeley has been based on statements quoted from the Atomic Energy Commission Safety Regulations: Adequate protective equipment shall be supplied for protection against hazards arising from production operations n.hich cannot be eliminated or effectively controlled by suitable engineering methods. . . Personal protect,ive equipment shall not be used as a substitute for elimination or control of hazardous conditions. I t has been impossible with the time and manpower available t o apply these principles to all the radioactive work of over a hundred chemists, physicists, and others engaged in genetics, physiology, biology, agriculture, medicine, and chemistry; much work is still being conducted in the old manner, but the most hazardous and most difficult problcms have been solved satisfactorily. The radioisotopes available from Oak Ridge a t this time are all beta- and/or gamma-emitters, with the exception of polonium, which is an alpha-emitter. From values for the quantity in grams for 1 curie of these isotopes against half-life it can be realized that in every case pure isotopes would be present in milligram quantities, and even if carrier is included there would never be an occasion when more-than-gram quantities of material would be involved in an experiment. Some idea of the shielding requirements in experimcnts can be obtained by reference to plots of energy against inches of lead. Radioactive material arrives in a closed container which can be introduced into a closed work box before i t is opened. Such a box is maintained a t a slight negat,ive pressure by its own individual blower which changes the air perhaps three or four times per minute. Adequate filters are installed in the line of the blower to remove whatever activity may be present in the air over the particular experiment. By adequate is meant suitable material in sufficiont quantity to remove the activity, whether two, three, four, or more filters are put in series. Waste active wash water or solutions are put into a sink which can be emptied through a line by suction into a properly shielded vacuum flask outside the box and the active waste collected and disposed of without opening the waste bottles. Thus the entire work is conducted without having the active material ever exposed. A s a general rule, the entire chemical process involved in any experiment can be carried out remotely by planning vacuum or pressure transfer of material, electric motor stirring, etc., with an occasional use of t'ongs and other special devices. The equipment and gadgets developed for these processes must be considered still very elementary modcls and naturally we have improvements to be incorporated in the next modcls. It has been hoped that others might take up this same philosophy and cont,ribute additional good ideas. The pooled results should produce wonderful equipment for safe efficient work with radioactive material. Incidentally, in addition to the other advantages of this approach, the indications are that many thousands of dollars may be saved in the construction and operation of laboratories. RECEIVEDAugust 28, 1948. Based on work performed under Contract W-7406-eng-48 for the Atomic Energy Project a t Radiation Laboratory, University of California.
