H. 1. Crater1, J. 8. Macchione2, W. J. Gemmill, and H. H. Kramer
Union Carbide Corporation Sterling Forest Research Center Tuxedo, New York 10987
Radioisotope Generators for Introductory Laboratory Use
M o s t high school and basic college science curricula include some discussior~of nuclear theory, but the extent and value of thc discussion are limited by an almost complete lack of meaningful experiments available to the instructor. There are a number of reasons for this lack, hut the most important is the inability to obtain radioactive isotopes in a form that meets satisfactory standards of economy and convenience. We conducted a study to determine whether radioisotope generators (a miniature vcrsion of those now widcly used in medical diagnosis) could meet these criteria; and when it became apparent that they could, we expanded our study to determine what principles of nucleonics could be demonstrated and to develop some simple experiments that high school students can perform with a minimum of laboratory equipment. These experiments were then performed by two just-graduated high school boys with gratifying results. Radioisotope Generators
For most elements in the periodic table, one or more of the isotopes can be made radioactive, and when decay occurs, an isotope of a different element, and therefore different chemical properties, is formed. Advantage can be made of this to separate the daughter from parent element, by choosing an absorber which strongly bonds the parent, but from which the daughter can be eluted easily. For example, radioactive cesium-137 can he fixed on a granular absorber in a column similar to an ion exchange column, and the decay product, harium137m, can he almost quantitatively eluted with an acidic solution, leaving the undecayed cesium in the column. Such a system is called a radioisotope generator. Since the whole field of generator technology is relatively new, and most of the development has been directed toward medical diagnosis, the miniaturized generators (Minigenerator) we used had to be developed specifically for this study. We used cesium-l37/ barium-l37m and tin-113/indium-113m generators that contained General Licensed amounts3of the parent radioisotopes (1 microcurie and 10 microcuries, respectively). The decay scheme of both these radionuclides is shown in Figure 1. The 30-year cesium-137/2.6-min barium-137m generator is attractive as an educational aid because of the Wltrwick;Valley High School, Warwick, New York. 'Kakait Jr. High School, Rsrnapo School Jhtrict No. 2, Spring Valley, New York. 3 Exempt from special licensing. These qosntitie? are generally licensed quantities-USAEC Rules and Regulations, Title 10, Part 31. 1
Figure 1 . Decoy scheme-Cesium-137 1 1 3 (right).
(left); and decoy scheme-Tin-
contrast in half-lives. The long-lived parent provides a column that can be used for years, while the 2.6-mi11 half-life of the daughter is ideal for decay and build-up studies. After being eluted, the generator returns to secular equilibrium within a few minutes; in fact, it call be milked every 2.G min with a yield of 50y0 of the barium-1.77111 activity produccd when equilibrium is established. Hence, it can be milked many times even during a very short laboratory period-a virtual faucet of a short-lived radioisotope. The lL5-day tin-113/100-min indium-1131x1 generator complements the cesium-137/barium-137m generator for educational use in several ways. Indium-113m has a longer half-life (long enough to perform experiments that require an appreciable portion of a laboratory period) and i t emits a gamma ray whose energy is slightly more than one-half that of barium-l37m (ideal situation for instrumental calibration and gamma raymatter interaction studies). Together, these generators appear to have the nuclear characteristics that are well suited to a classroom situation. Development work on a generator design suitable for classroom use was carried on throughout the studv. ", and the final design of the Minigenerator is shown in Figure 2. The column of the generator is sized so that it can be used as a point source of radiation and can he placed directly in the counting chamber of a radiation detector. A plastic squeeze bottle (seeFig. Z), charged with the eluting solution, can be used to force the solution through the Minigenerator inahout 30 see. ~i~~~~ 2. Minigenerator. Volume 46, Number 5, May 1969
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Thr :idv:u~tages of this pressurized elution include ensier handling of the eluant, and fast,cr elut,ion of the llinigcnerntor. A major advaut,age of the hlinigenerator is that it is an inexpensive source of short-lived radioisotopes. It can deliver well over 1000 times its loading during its uscful lifctime which is many years for the cesium-1371 barium-l37m generator and about one year for the tin113/indium-l13m generator. I n addition, the generator call he eluted whenever desired and repeatedly during a given laborat,ory period. This characteristic
virtually eliminates the supply and demand problems often associated with ot,her commercially available radioisotopes. The Study
The facts of school financing required that we observe self-imposed financial limit,ations. There is no point in specifying curriculum materials that cost more than a school board will buy. Therefore, we limited ourselves to the least expensive detecting and counting equipment that would give us reproducible results. Listed below
Radioisotope Experiments
Title
How Generator was Used
1 Opernting Characteristics of s. Radiation Detector
Either generator used as point source
2 Resolving Time of Radiation Detector Equipment
Indium-113m eloted fram generator
3 The Gaussian or Normal 1)istrihntion
W n / n 3 m I n generator used as a m i n t source
4 Generator Elr~tion
Indium-113m eluted from generator
5 Parent/Da,lghter Equilibrium
137Cs/'a7'" Ba generator nsed as source after elution
6 Half-life of Barit~m-137m
Barium-l37m eloted from generator Indinm-113m eluted from generator llaSn/l'amIn generator nsed as a point source
7 Half-life of Indiom-ll3m 8 Inverse Square Law
Absorption of Gamma Photons
flaSn/"amIn generator used as a point source
10 Energy of Gamma Rays
Bath generators used a5 point source
11 Pulse Height Analysis
Bol.h generators used as point source 1"911/"~'"In generator used as a point source
I)
12 Campton Scattering 13 Precipit,ation of Indinm Hydroxide
Indiom-113m eloted from generator Indiom-113m eluted from generator
Solution
15 Rearlions Between Ions in Aqueous Solut.ion 16 Gauging 17 Tracing 18 Hate of Flow in Fluids 10 1)etcrminstian of the Volume of a Container 20 1)etermination of t,he Amorwt of Fluid in a Container 21 Washing Efficiency
generator "3Sn/L13"'In generator used as m i n t Source Indi~im-113ieluted from generator Indium-113m eluted from generator Indium-113m elnted from generator Indium-ll3m eluted from generator
22 1)iffnsion
Indium-113m eloted from generator Indimn-ll3m eluted from generator
23 Wear Stndies
Indinm-ll3m eluted from generat,or
Pnrpose T o determine the operating voltage of a radiation detector T o determine the resalving time of a radiation counter using t h e paired (split sonree) method T o investigate the statistics of radioactive measuremellts T o determine the amount of eluant required for a. total yield of radioactive indiom-113m T o stndy the transient equilibrium between a radioactive parent and a radioactive daughter T o dokrmine the halflife of barium-137m T o determine the decay rate of indium-113m T o determine t h e effect of distance fram a radioactive source on t h e intensitv of its gamma mdiation To determine t h e half-valuelayer of lead shielding for gamma rays To qoant,itatively measure and compare the energies of gamma rays from several radioisotopes T o stndy gamma-ray energies using an oscilloscope To detect srattering of gamma rays passing through matter To investigate the use of r a d i o s c t k tracers in a chemical reaction T o enable the stndent t o ausntit,ativelv determine change in ¢ration of an ion in solution when a second reagent is added; T o introduce t h e student lo soluhilit,y studies T o determine end product,s in a theoretical equation Densit,y gauging T o trace internal systems T o measure rate of fluid transmission within a. closed system T o determine the volume of an irregular container To determine the a m o ~ t n of t fluid in a container
of indium-113m ions through s, membrane To detect evidence of wear from friction
are the models aud prices of the equipment we used (it was bought from Kuclear Chicago Corporation, but several other companies supply comparable equipment at competitive prices) Model 8770 Scaler $360 Model 403 Seintillat,ion Iletection System 360 Model 8428 Dnal Timer 60 Model 6323 Classmaster I1 Geiger System 200
The only other material requirements for the experiments we developed are a cathode-ray oscilloscope and the ordinary supplies and glassware usually found in a high school laboratory. We checked the efficacyof our generators aud the functiouiug of our equipment by performing two traditional experiments-demonstration of the inverse-square law and the determination of halflife. Our accuracy and reproducibility were both well within satisfactory limits. Beyond performing these classic demonstrations, our approach to experimentatiou was trial and error to the extent of immediately trying out an experiment as it was conceived. Wc limited ourselves to experiments that could be completed in one classroom laboratory period and that demonstrated a single principle of nucleonics. I n general, we found that the generators could accomplish anything that presently available gamma-ray sources can. A summary of the experiments we devised is giveu in the table. Since our entire study was carried out duriug a ten-week summer vacation period, it is obvious that this list could be greatly expanded with further work. The Experiments
Used as point sources, the Minigenerator functioned dependably to demoustrate basic detecting and measuring principles (Experiments 1, 3, 8-12 and 16). When the generators are eluted, the isotopes served to show the decay and build-up properties of radioactive materials (Experiments 4-7). In addition, the eluted radioiso-
topes are in a useful liquid form to serve as tracers in ion studies (Experiments 13-15 and 22), and they can be used to demonstrate some common industrial applications (Experiments 17-21 and 23). All the experiments in the table were performed by two moderately gifted, very recent high-school graduates over a six-day period. I t was most gratifying to observe the students' transformation from rather timid experimenters to enthusiastic and engrossed participants within a few days. We attribute this growth to the students' satisfaction at having the experiments "work out": they consistently obtained accurate results when using the Minigenerator and instruments according to procedure. By the end of their six-day study, the students exhihit,ed an excellent grasp of nucleonics principles and subject matter. They agreed emphatically that experimentation was needed to bring such concepts to life. Conclusion
To have lasting value, education in nuclear theory must be supported by a program of laboratory demonstration and experiment. Such a program requires a source of radioactivity that (1) is within the financial means of limited high school budgets, (2) can be stored and easily handled even by inexperienced people, (3) is available for use throughout the school year, and (4) can be used to perform a broad spectrum of experiments. We feel that the radioisotope i\'Iinigenerator used meets these criteria, and do not feel that we have come near exhausting their possibilities. The Minigenerator could be used for the most basic pre-high school demonstrations, to illustrate the parts of present chemistry and physics curricula that deal with nuclear theory, and to develop a separate high school nucleonics course for advanced science students. I n addition, they could he used to advantage in technician training, in terminal two-year college courses and in various undergraduate college courses.
Volume 46, Number 5, May 1969
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