ANALYTICAL CHEMISTRY
1004 the Massachusetts Institute of Technologj , \rho kindl? -upplied the circuit for the square wave modulator, and t o I,. G. Larikford and G. W. Cartel for the excellent machine work i n th(3 con+tructionof the Stark cell used in this investigation LII EK i n H E CITED
Bailey, B. P., Kyhl, It. L.. Strandberg, M. W. P., \.an Vleck, J. H., and Wilson, E B., Jr., Phys. Rev., 70,984 (1946). 12) Rleaney, B., and Penrose, R. P., Proc. Phys. SOC.,59,418 (1947), 60, 83, 540 (1948); -\-u~uFP. 157,339 (1946); Proc. Roy. Soc., A189,358 (1947). ( 3 ) Calvin, Heidelberger, Reid, Tolbert, and Yankwich, “Isotopic Carbon,” New York, John Wiley & Sons, 1949. (4) Cleeton, C. E., and Williams, K.H., Phys. Rev., 45,234 (1934). (5) Coles, D. K., and Good, W. E., Ibid., 70,979 (1946). (6) Garcia de Quevedo J. L., and Smith, W. V., J . A p p l i e d Phus., (I
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19, 831 (1948). (7) Good, W. E.,Phys. RPV., 70,213 (1946). ( 8 ) Gnrdy. W., Rei, M o d i r n Ph!is 20,A68 (1948)
Hughes, K . H . . and N.ilsoii, E:. H., ,Jr., Phgs. R e i . . 71, 562 (1947). Kharasch, Stiles. Sensen, arid Lewis, Ind. ETIY.Chem., 41,2840 (1949). Kisliuk, P.. aiid Townes, (‘. H.. . I . Research S a t l . Bur. Stcindnrds, 44,611 (1950). IIichels, W.C., and Bedding, E:. I)., Reo. Sci. Ircstrun~mts.20, 566 (1949).
Montgomery, “Techniques of Microwave Measurements,” Vol. 11, SIIT Radiation Lahoratory Series, Xew Tork, McCraw-Hill Book C‘ runrc,!ifs, 21,120 (1950). Smith, TI-. V., (;ai& cle Qurwdo. .J. I,.. Carter, R. I,.. and Bennett, W. S.,J . A p p l i e d Ph,p.. 18, I112 (1947). Townes, C. H., Holden, A . S . , arid Merritt. F. K.. P h y s . Rcu., 71,64 (1947). I hid., 74, 1113 (1949). UECEIYED April 10, 1Q50. Based o n work perfornied under contract for the .iromic Energy Commission b y the Isotope Research and Production Division, Oak Ridge National Laboratory, Y-12 Area, Carbide a n d Carbon Chemicals Division. Iinion Carhide and Carbon Corp.. Oak Ridge. Tenn.
Detection of Trace Quantities of Radioactive Materials in Waste. Streams PAUL K. FIELDS W D GRAY L. PYLE -4rgonne Yational Laborutory, Chicago, Ill. Some general considerations in determining microquan tities of radioactive isotopes are presented. In order to concentrate on the radiochemical problems, the general analytical chemistry has been limited to uranium, as an example of an alpha emitter, and to 1131, as an example of a beta emitter. A fluorophotometric method and a radiochemical method of determining uranium are discussed. Some of the problems encountered in analyzing and identifying betaemitting isotopes are illustrated by a procedure for isolating Ii31from a waste solution. Certain corrections must be applied to the recorded beta count to obtain the absolute disintegration rate.
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HIS paper is intentfed to serve as a brief introductioii to radiochemistry for waste disposal scientists who have had little or no experience in the field of radioactivity. In order to wnplify the coverage of such a broad and complicated subject, the general analytical chemistry is limited here to only two rlem ~ i i t s IJranium is taken as an example of an alpha emitter xiid 1‘3’ an example of a beta emittrr. IC
PERMISSIBLE LEVELS OF RADIOACTIVITY . i t a recent Riastme Disposal Symposium (11) lO-’microcurie per milliliter of alpha and beta activity mas proposed as the probablt. niasinium permissible c.oncentrat,ion of general radioactive contaniinant,s in a water supply outside a controlled area. This, with other considerations diwuwtd below, must be kept in mind when < h i d i n g on the volumrs ( 1 1 \\ aste solutions to he taken for an;rly-
lost in qaniple‘~of VWIOUS suifiic~derislties can he seen in Tahle I (6). In beta counting a larger aliquot must be taken than in alpha counting, because the natural background of a beta counter is about 25 counts per minute whereas that of the alpha counters is practically zero. Therefore, 1 liter of the solution may be evaporated to dryness under alkaline conditions. The solid residue, when spread over an area of approximately 6 sq. cm., would be about 50 mg. per sq. cm. This sample could be counted with an end-window Geiger counter, the windows of which are generally about 8 sq. cm. in area. Only the very soft betas would be missed by this method; these would require special techniques. Examples of isotopes emitting soft betas-Le., beta rays with very low energies-are Ci4 and 8%
*is.
The following prwcdure would probably be satisfactory for crlet,ecting the presenw of this level of activity. For ail alpha assay, about 25 ml. could be evaporabed to dryness in a flat metal .dish about, 10 sq. cm. in area. Assuming lo-’ microcurie prr milliliter, the sample would contain 2.5 counts per minute, lwel of alpha activity that can easily be determined iii a11 ordiI I : I I . ~ alpha counter. Unless there was more than the usual amount of nonvolatile material in the water, this aliquot aould give :I dry residue of a little less than 1 mg. per sq. cm. .Ilt,hough this is a little thick for alpha counting, the amount of alpha activity could he determined with fair accuracy, provided t,he inat
