(10)Ketellc, B. H., Boyd, G. E., J . Am. Chem. SOC.69, 2800 (1947). (11) Moore, F. L.,ANAL.CHEM.29, 1660 (1957). (12)Zbid., 30, 908 (1958). (13)Pressley, R. S., Oak Ridge National Laboratory Unclaeaified Rept. ORNL2202 (1957). (14) Rabideau, S. W., Aeprey, L. B., Keenan, T. K., Newton, T. W., Ptoc. and Intern. conf. Peaceful Uses Atomic Energy 28, 361 (1958). (16) Stewart, D. C., Proc. Intern. Conf.
Peaceful Uses Alomic Energy 7 , 321 (1956). (16) Street, K.,Jr., Seaborg, G. T., J . Am. Chem. SOC.72 2790 (1950). (17) Surls, J. P., dhoppin, G. R., J. Znorg. & Nwlear Chem. 4, 62 (1957). (18) Thompson,. 8. G., Harve B. G.,
6:
Chop in, 0. R., Seaborg, T., J. Am. 8hsm. SOC.76, 6229 (1954). (19) Thom son, 8. G., Mor ant L. O., James, A., Perlrnan, in “The Transuranium Elemente,” kNESIV14B p 1339-61, McGraw-Hill, New York, PQ49.
8.
f
(20 Tom kina, E. R., Khyrn, J. X., John, E., J . Am. Chem. SOC.69, 276%77 11947). (21’ Wish ‘LI,-.Freiling, E. C., Bunney, L. R., Zbid., 76,3444 (1954).
6.
RECEIVED for review November 21, 1960. Accepted February 16, 1961. Work performed et Oak Ridge National Laboratory, operated b Union Carbide Nuclear Co. for the .&,omic Ener Commission. Divieion of Water and #mte Chemistry, 139th Meeting, ACS, St. Louis, hlo., March 1961.
Solvent Extraction of Technetium and Rhenium with Pyridine or Methyl-Substituted Pyridine Derivatives from Alkaline Media S. J. RIMSHAW and G. F. MALLING Isotopes Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
b
Pyridine and its methyl-substituted derivatives have been applied as specific extractants in the isolation and purification of pure technetium and rhenium compounds from alkaline solutions. The behavior of these liquid amines is generally analogous to that of the solid amine anion exchangers. Thus, the distribution coefficients decrease with increasing concentrations of nitrate ions. Nevertheless, 2,4dimethylpyridine showed a distribution coefficient of 50 for technetium in 4.ON N a N O r 0 . 5 N NaOH. The method is useful in analytical or preparative work. The pyridine compound is steam-distilled as the free amine. Technetium metal is obtained by crystallization of ammonium pertechnetate from 4.OM (NH4)2COa followed by reduction with hydrogen.
L
AMINES (17) have been used to remove mineral acids from acid hydrolyzates of protein solutions. The strongly basic solid anion exchangers have been used widely to arrive at a better understanding of metal anionic complexes in solution. Although the general chemical behavior of the liquid amine and the solid amine systems are similar, the manifold advantages of liquid-liquid extraction compared to solid-liquid contacting have been enumerated (14). In addition, Coleman et al. ( 7 ) investigated a number of long-chain amines as specific extractants for uranium on an industrial scale. They showed that the extent of branching in the over-all structure of the amine controls the specific extraction behavior through a combination of electronic and steric effects. ONG-CHAIN
Boyd, Larson, and Motta (6) were the first to show that the strong-base anion exchangers have a high affinity for technetium and rhenium.- They reported a distribution coefficient of 1300 for technetium and one of 590 for rhenium from 0.1N HCl. Atteberry and Boyd (1) used Dowex 2 to separate technetium and rhenium by ionexchange chromatography at a p H of 8.3 to 8.5. As expected from the respective distribution coefficients, rhenium was eluted from the column before technetium ( I , 2). Fisher and Meloche (9) investigated the separation of small quantities of rhenium from relatively large amounts of molybdenum on the anion exchanger Amberlite IR-400. Because of the high affinity of the anion resin for rhenium, perrhenate ions would displace molybdenum from the resin. Molybdenum was eluted selectively from the column with 2.5N NaOH. Rhenium can be eluted satisfactorily with 1.OM HCIO, (18). Analogous behavior of technetium and rhenium when extracted into the aromatic amine pyridine has been reported in the literature. Goishi and Libby (11) found that the distribution between pyridine and 4.ON NaOH is 8000 for manganese, 778 for technetium, and 225 for rhenium. Boyd and Larson (3)report a distribution coefficient of 180 for technetium from 1.ON NaOH with 0.1M pyridine in cyclohexane. Gerlit (10)reports a distribution coefficient of 39 for technetium and of 24 for rhenium from 5.ON NaOH withpyridine. Faddeeva, Pavlov, and Bakunina (8) purified the 6-hour TcQ9daughter from Mo90 by extraction with methyl ethyl ketone (MEK) from 3.OM &CO,. This paper demonstrates the use-
fulness of solvent extraction by pyridine bases from alkaline media in the preparation of pure technetium or rhenium compounds. EXPERIMENTAL
Materials. The technetium, rhenium, and fission product tracers used in the experimental investigations were Tc9), TcgQm, Re’ss ZrQ6-Nb96, C P , R U ~ W ~ U 1 6 * - 1 m , a n d Srm. T i e 6-hour Tcgsmwas separated from its parent, 67-hour MoQQ,by solvent extraction with methyl eth 1 ketone from an aqueous solution a4usted to 2.OM Ned308 and 0.25M NaOH. The organic phase containing the TcoDm was washed twice with a solution of the same composition as the aqueous. Additional TcQQW could be extracted from the MoQo in 24 hours when required. Decay studies showed t h a t the technetium tracer prepared in this manner was more than 99.9% radiochemically pure. Irradiation of molybdenum metal on a cyclotron with 22-m.e.v. protons gave the 4.2-day TcM, 60-day TcQ’ mixed tracers. The target was dissolved by treating with strong nitric acid. Molybdenum metal was converted to Moos, which separated from the acid solution as a white precipitate. Neutralization with caustic resulted in a clear solution of sodium molybdate. The technetium ,tracer was then extracted from this solution as previously described by extraction with methyl ethyl ketone from an aqueous phase 2.OM in NaZCO, and 0.25N in NaOH. Radiochemical punty of the tracer was 99%. Boyd, Larson, and Motta ( 4 ) have recently reported an alternate method for purification of this tracer which involves a preliminary separation of technetium from molybdenum on Dowex 1anion exchange resin. VOL 33, NO. 6, M A Y 1961
751
Tlic Rel*O trnrcr \vaR obtained by neutron irrndint,ion of rhenium metal. A iwriod of 1 moiith had elapscd sincc the tracrr was formcd, so that all of thc: Rei# had decayed. 'rhc other fission product traccrs, obtained from the Isotopes Division of this laboratory, were pure enough to meet catalog spccifications (radiochemical purity >99%). Activity measurements for all of the tracers except Srw and Tcsg were made on a single-channel gamma spectrometer having a thallium-activated sodium iodide crystal. Samplrs were differentially analyzed ovcr thc desircd energy range to minimize the error of even the slightcst impurities. A sample taken at the beginning of each ex criment scrvcd as a reference stan ard for decay correction where necessary. Radiochemical analysis for the longlived Tc99 (half life, 2.12 x 10' years) was performed by adding rhenium carrier to the sample and isolating the technetium and rhenium after various scavenging steps to eliminate other radioactive impurities (16). Yield corrections were made by weighing the
cf
Table 1. Distribution Coefficients of Tc into Pyridine and Methyl Ethyl Ketone as a Function of NaOH and Na2C03 Concentrations
(Traccr, 60-day T P ) KD,TC Concn.! Mol-/ Extn. Extn. 1,iter with with NaOH Narc08 pyridine MEK 1.0 ... No phase aepn. 20.5 2.0 ... 64 40.3 3.0 ... 239 50.3 4.0 371 60.0 0.50 0.25 No phnse sepn. 16 0.50 0.75 26 0.50 1.25 229 98 47 0.50 1.75 281 50
Table II. Distribution Coefficients of TcD6with Pyridine and Anion Exchanger Dowex 1 as a Function of NaNOa Concentration
(NaOII, 2.ON for pyridine and 0.25N for Ilowcx 1; tracer, GO-day Tc96) A . NaNOa 'Loncn. KD nmes/fi.
Ext. with Pyridine 0 54 0.5 19 1.0 16 1.5 12 Sorption by Dowex 1 0 4500 0.5 575 1.0 340 2.0 l!N 3.0 142 4.0 125 5.0 121 G.0 122
amount of rhcnium recovcrcd. The 0.22-m.e.v. 0-particles from Tcg9 were counted on a thin (1.5 to 2.0 mg. per sq. cm.) end-window Geiger-Mueller counter. The radiochemical analyses for technetium were cross-clieckcd regularly by carrying out a polarographic analysis for technetium (6,IS), which can detect as little as 0.05 p.p.m. of technetium. The results from the two methods a reed within 10%. Methods. f n the tracer-level extraction experiments, 50 ml. of aqueous phase was contacted with a n cqual volume of organic solvent. The organic solvent was equilibrated previously with a solution of the same composition as the a ueous phase. After 5 minutes of shaiing and a complete phase separation, the organic and aqueous phases were analyzed. The distribution coefficient was calculated as the ratio of the count rate per unit volume found for the organic phase to that found for the aqueous phase. The count rates in the respective phascs were determined as counts per minute per milliliter with the same scintillation counter. Three small misor-settler extractors were used in series to conwntrate and purify trchnetiuni. The extraction vessels were made of horosilicatc glass, each mixer unit having a total volume of 4 liters. Connccting lines and valves were made of stainless steel, and Tygon connections were used to join the metal to the glass units. Air agitation was used on the mixers. Liquids were transferred between stages using vacuum. In each run, five batches (2.0 liters each) of aqueous phase were each successively contacted with the three extraction stages in series (0.5 liter of organic phase each). Then, the organic phase at the head end of the process was wi'thdrawn, since it contained the highest concentration of technctium. The organic phases in other units were moved forward by one unit, and fresh organic solvent was added to the tail end of the process. This procedure was repeated systcmatically. The organic and aqueous phases were sampled to determine distribution coefficients for technrtium. The fccd solution, which had been partially purified at the Fission Products Pilot Plant at this laboratory, was 1.ON in "08 and contained 0.5 to 1.0 gram per liter of technetium, with Ce144 and Ru1W as the rincipal radioactive contaminants. T\e solution was neutralized with caustic and extracted with pyridine or a methyl-substituted pyridine derivative to prepare pure technetium compounds. The st.rong-base anion exchanger waa Dowex 1, 100- to 2OO-mesh, 10% crosslinked. In each experiment 50 ml. of aqueous was contacted with 1 gram of air-dried resin. A distribution coefficient was calculated from the gamma count ratea of the aqueous phase before and after contact with the resin as follows: KD
i
-f f
752
ANALYTICAL CHEMISTRY
wt. of aqueous wt. of resin
wlirri* i is thr! initinl count, rritr and is tlio find c w n t ratc. RESULTS
Distribution cocficicnts for the extraction of GO-day Tee6 into pyridine and methyl ethyl krtone were determined aa a function of NaOH concentration in the aqucous phase ('l'ltblc I ) The K D for technetium incrrnses with increasing NaOH concentration. Fyridine shows a higher affinity for technetium than methyl cthyl kctone docs. The behavior of technrtium with pyridine and methyl ethyl ketone wm again compared aa a function of NaZCOs concentration. The use of 0.50N NaOH in each experimcnt led to a better separation of phascs. The rcsults are also presented in Tablc I. Again it is obvious that pyridine is the better performer. Since the uranium carbonate complex docs not extract, this system is also useful in separating technetium from uranium compounds. Morgan and Siecland (16) show that the affinity of technetium for the anion exchanger Amberlite IR-4B decrcwcs with increasing nitric acid concentration, prcsumably because of competition from the nitrate anion. Hence, the extraction of technetium into pyridine from 2.ON NaOH was investigated a function of sodium nitrate conccntration. In addition, distribution cocfficients of Tc96 between the anion exchanger Dowex 1 and 0.25N NaOII were determined aa a function of sodium nitrate concentration. These data are presented together in Table 11. Nitrate decreases the affinity of technetium for the anion resin and the liquid amine. The behavior in both systems is analogous. Distribution coefficients for technetium and rhenium between pyridine and 0.25N NaOH-2.0M NanCOs were determined as a function of sodium nitrate concentration. The results are prcscnted in Table 111. The data show that the distribution coefficients for technetium and rhenium fall with increasing sodium nitrate concentration. In agreement with previous observations made on the behavior of technetium and rhenium with analogous systems of amines, the distribution coefficient for tcchnetium is consistently higher than that for rhenium under comparable conditions. Distribution coefficients of technetium and rhehium between pyridine and 0.25N NaOH-2.0M Na2COa were investigated as a function of the concentration of technetium and rhenium in the aqueous phase prior to solvent extraction. The results are presented in Table IV. The distribution coefficients of both technetium and rhenium fall with an increase in loading of the organic phase. Under comparable
conditions, the distribution coefficients for technetium are higher than those for rhmium. Separation of Technetium from Fission Products. Since technetium
is a fission product with a yield of 6.4y0, its separation from other fission products is a matter of interest. A number of single-tracer experiments were performed to determine the distribution coefficients of various fission product elements between 0.25N NaOH-2,OM NaZCOa and pyridine. The results are presented in Table V. Technetium can be readily decontaminated from other fission products by this method. Technetium Distribution Coe5cients under Operating Conditions.
A sollition containing 0.15 gram per liter of technetium was obtained from the Fission Products Pilot Plant of this lttboratory. The solution was neutrrtlized, resulting in concentrations of 0.25N NaN03-2.0M NalCOa0.5N NaOH, and found to contain a small amount of an oil. Analyses of the aqueous and organic phases after extraction with pyridine indicated an average distribution coefficient of 37 for technetium. Competition from the nitrate ion and the presence of the oil, which extracted into the organic phase, lowered the distribution coefficient for technetium (3,10). The technetium was recovered from the above organic and used to make a new feed solution 2.0211 Na&Oh0.5N NaOH containing 20 grams per liter of technetium. Oil was still present, but the nitrate had been eliminated by the fimt extraction. The technetium distribution coefficient was 47 for extracting this feed with pyridine. Substituted Pyridine Compounds as Extraction Reagents for Technetium. Although pyridine extrac-
tion of technetium is adequate from 2.OM N:tCOs or 4.ON NaOH, various methyl - substituted derivatives of pyridine performed better in 2.OM (NH,)GO, or in aqueous solutions with a high nitrate concentration. Thus, in 2.OM (NH4)2C03solutions, the respective distribution coefficients of pyridine and Zmethylpyridine for technetium are 7.5 and 242. The &methyl- and 4-mrthylpyridine derivatives show even higher distribution coefficicnts for technetium than Zmethylpyridine does. The addition of pyridine to an alkaline solution containing high concentrations of sodium nitrate results in saltingout of sodium nitrate because of the solubility of pyridine in the aqueous phase. On the other hand, 2,4-dimethylpyridine showcd a distribution coefficient for technetium of 50 in 4.ON NaNOa0.5N NaOH. Lutidinr did not salt out any sodium nitrate. Hence, it may be concluded that the methylsubstituted derivatives of pyridine are
useful in separating technetium from appreciable amounts of nitrate ions. Purification of Technetium. Pyridine or a methyl-substituted derivative of pyridine is conveniently separated from technetium by distillation. Pyridine forms an azeotrope with water t h a t boils at 93" C., and 2,4methylpyridine forms an azeotrope t h a t boils a t 98" C. Water is added during the steam distillation of the volatile amine to obtain an aqueous solution of technetium. The steamdistilled pyridine compound is pure and can be re-used. Organic impurities are concentrated along with technetium in this process. Extraction from 0.3N HNOs with a nonpolar solvent such as chloroform, benzene, hexane, or kerosine will remove many organic impurities and leave technetium in the aqueous phase (9, 10). Some of the organic impurities remain associated with technetium in the aqueous phase since the separation is never sharp. The technetium losses to the nonpolar solvent are low (99%. No radiochemical contaminants can be detected. I t is preferable to isolate the ammonium salt rather than the potassium salt of technetium because of ita solubility in water and because the ammonium salt can be used directly to prepare pure technetium metal. Preparation of Technetium Metal.
The standard procedure for preparation of pure rhenium metal involves the reduction of ammonium perrhenate at 300" C. for 1 hour and 1000° C. for 2 hours with hydrogen (18). Technetium is reduced more readily than rhenium. Thus, Cobble et al. (6) found that a mixture of N H r Tc04 and (NH&S04 gave a black mass of TcOz on hydrogen reduction a t a low temperature. On continuing the reduction a t 500" to 600" C. they volatilized the (NH4)&304 leaving behind 0.6 gram of spectrochemically pure metallic technetium. This procedure was used to produce pure technetium metal from NHdTcO4. I t is necessary to heat slowly to 200" to 225' C. and hold at this temperature for about 1 hour. If the heating is too rapid, some of the technetium will be volatilized in the reduction of NH'TcO4 to TcO,. After the reduction to TcOz is complete, the temperature is raised to 600" to 800' C. for 1 hour t o reduce TcOz to technetium metal. Ten grams of technetium metal were prepared in this
Table 111. Distribution Coefficients of TC and Re between Pyridine and 0.25N NaOH-2.0M NanCOD Solutions as a Function of NaNO, Concentration
(Tc tracer, m a y Tc"; Re tracer, Re'") A NaNO, %on cn ., Molea/L. KD, Tc KD,Re 0.25 110 59 0.50 89 54 71 44 0.75 1 .o 58 32 52 29 1.5 42 23 2.0 Table IV. Distribution Coefficients of Tc and Re between Pyridine and 0.25N NaOH-2.0M Na2COI as a Function of Concentration of Tc and Re in Aqueous Phase
(Tracers, Re" and long-lived TcoD) Initial A Concn., Role/L. KD TECHNETICUM 0.172 04 0.086 203 0.0434 324 0.0087 740 RHENIUM 0.16 28 0.08 37 0.04 46 0.008 64 Table V. Distribution Coefficients of Various Fission Product Elements between 0.25N NaOH-2.0M NazCOa and Pyridine
Fission Product Ce'"
Ru lW Zr96, Nb06 &I63
Sr *
-166
KD 2.87X lo-' 1.27 X lo-' 6 X IO-' 6X
lo-'
3.48 X
way. The technetium metal was massive in form and silvery gray in color. No tarnishing was observed on leaving the metal in contact with air. Spectroscopic analysis showed less than 1 p.p.m. of sodium, molybdenum, magnesium, and silicon. ACKNOWLEDGMENT
The authors thank R. R. Rickard of the Analytical Chemistry Division of the laboratory for his valuable assistance. We are also indebted to D. C. Winkley for the results in Table V and for his help with various phases of this project. LITERATURE CITED
(1) Atteherry, R. W., Boyd, G. E., J. Am. Chem. Soc. 72, 4805 (1950).
(2) Boyd, G. E.,Lnrson, Q. V., J . Phys. C h . 60,707 (1956). VOL 33, NO. 6, MAY 1961
* 753
(3) Boyd, G . E., Larson, Q.V., Zbid., 64, 988 ( 1960). (4) Boyd, G . E., Lamon, V., Motta, E. E.,J . Am. Chem. oc. 82, 813, (1960). ( 6 ) Boyd, 0. E., Lareon, Q. V., Motta,
s.
E. E., U. S. At. Energy Comm., Rept.
AECD-2151 (June 1948). (0) Cobble, J. W., Nelson, C . M., Parker, G.W., Smith, W. T., Jr., Boyd, 0. E., J . Am. Chem. SOC. 74, 1852 (1952). (7) Colemnn, C . F., Brown, K. B., Moore, J. C..Allen. K. A.. Proc. Intern. Conf. Yencrful Uers Atomic Energy, Geneva, Paper €’/510 U.S.A. (1058). (8) Faddeeva. M. S.. Pavlov. 0. N..
. ,Bakuniiia,
V. V., Zhur. Neoig. Khim:
3, !65 (1958). (9) Fisher, 8.A., Meloche, V. W., ANAL. CAEM.24, 1100 (1952).
(10) Gerlit, J. B., Proc. Intern. Conf. PeRccful Uses Atomic Energy, Geneva 1965, VO~. 7, pp. 145-51 (1956).
(11) Goishi, W., Libby, W. F., J . Am. Chem. SOC.74, 6109 (1952). (12) Meloche, V. W., Preuas, A. F., ANAL. CHEM.26, 1911 (1954). (13) Miller, H. H., Kclloy, M. T., Thoma-
son, P. F., Second International Polarographic Conference, Cambridge, England, 1959. (14) Moore, F. L., ANAL.CHEM.29, 1660 (1957). (15) Morgan, F., Sizelmd, M. L., At.
Energy Research Establ., Gt. Britain, Rept. AERE-C/M-96, Harweli, England (1957). (16) Rickard, R. R., Wyatt, E. I., ORNL Mmter Anal tical Manual, Sect. 2. TID-7015. Lethod No. 2 21831 ( h n e 1960). ’ (17 Smith, E. L., Page, J. E., J . SOC. dhm. Znd. (Lon$n) 67, 48 1948). (18). Tribalat, S., Monograp on Rhenium and Technetium,” p. 9, GauthierVillare, Parie, France, 1957. RECEIVED for review September 23, 1960. Accepted February 9, 1961. Oak Ridge National Laboratory is operated by Union Carbide Corp. for the U. 5. Atomic Energy Commiesion.
6
Determination of Small Amounts of Cobalt Using Isotope-Dilution with Cobalt-60 K. F. SPOREK‘ Bioferm Corp., Wasco, Calif.
b An isotope-dilution method for the determination of cobalt employs cobalt60 as the tracer and a spectrophotometric procedure based on the extraction of cobalt thiocyanate with methyl isobutyl ketone. The extraction is carried out under neutral or slightly basic pH conditions and this makes the procedure virtually speciflc for cobalt. The method is suitable for the determination of cobalt at concentrations from a few parts per million upwards in biological materials, vitamin Bll, salts, metals, etc. When a well-type scintillation detector is used for measuring the radiation of cobalt-60 in liquid samples, the procedure is relatively simple and rapid. The results obtained in testing the behavior of a number of metals and the various stages of the extraction of cobalt thiocyanate with methyl isobutyl ketone, in the presence of cobalt-60 as tracer, are also presented.
T
HE
determination of small amounts
of cobalt is not simple, because of
lock of specific methods. With most existing procedures prior separation of cobalt or removal of interfering ions from thc tested sample is necessary. Even such traditional methods as those using 1-nitroso-2-naphthol and nitrosoR salt suffcr from interference by iron, chroniiuni, copper, nickel, manganese, and nitratc (2, 4 ) and many modifications of thesc methods, some rather laborious, have been developed to make thcrn suitable for specific purposes. 1 Present address, Owens-Illinois Technical Center, 1700 North Westwood, Toledo, Ohio.
754
0
ANALYTICAL CHEMISTRY
The recently introduced technique which employs tetraphenylarsonium chloride as reagent (1, IO), although better than the above, still requires separation or masking of iron, copper, molybdenum, vanadium, chromium, and nitrate. Other recently described methods with smaller or larger degree of specificity for cobalt use diethylenetriamine (7), oxamidoxime (9),and acetylacetone (8). However, they involve so many manipulatory steps that the possibility of errors and msociated lowering of precision is serious. The availability of radioactive cobalt60 and the ease with which its gamma radiation can be accurately measured suggested its use as a tracer in a chemical method which would be highly specific for the metal, and simple and rapid in operation, though not necessarily giving complete recovery from the tested samples. Work involving radiocobalt has been reported in connection with testing of recoveries of the metal following different oxidation procedures (6). Several analytical procedures using cobalt-60 as tracer have also been described; these, however, employed rather lengthy and laborious gravimetric trchniques (8, 11-19) and mere not suitable for the determination of cobalt in the 100- t o 500-pg. range. A method was required for the general determination of cobalt in vitamin Bl2 and in biological materials. Of several existing methods examined, the extraction of cobalt thiocyanate with a watcr-immiscible ketone undoubtedly provided a simple and fast procedure. However, many metals interfered (6) and it was necessary to find a means of overcoming this dif-
ficulty. A certain amount of experimentation was carried out and, under weakly alkaline conditions, cobalt W&B found to be the only metal extractable with a water-immiscible ketone [methyl isobutyl ketone (4-methyl-%pentanone), ethyl amyl ketone]. Based on this a spectrophotometric method was developed with radiocobalt used as tracer, thus making quantitative recovery of cobalt unnecessary in the extraction step and so simplifying the procedure further. Detailed investigation of the factors involved showed that the procedure described below is satisfactory for use with vitamin B12 and biological materials, and should be generally applicable for a large variety of other materials. EXPERIMENTAL
Apparatus. Scaling Unit, NuclearChicago Corp., Model 161A, operated at 1200 volts with the scale selection knob a t “256” value. This setting gave 1 unit on the mechanical register of the instrument for each 256 actual counts (actual counts X 256-l) ; because the calculations were simpler and the aecurac of results was not involved, the meclanical register units rather than the actual counts were used throughout this work. Well-type scintillation detector, Nuclear-Chicago Corp., Model DS-3, used with 16 x 150 mm. glass test tubes for counting liquid samples. Dual Timer, Nuclear-Chicago Corp., Model T1. Spectrophotometer, Beckman Rilodel DU, operated a t 620 mp with 1-cm. glass cells. Reagents. Radioactive Cobalt Solution. Cobalt-60 in the form of
