I
W. F. Semmelrogge and Fred Sicilio Texas A&M University College Station
A Study of Sedclr Equilibrium
I
Using
~e'"- ~ r ' "
count rate meter and recorder, for the second set.
The subject of secular equilibrium is discussed in many texts (1-4). Various authors have suggested experiments to aid the student in learning the fundamentals of radioactivity in a pair of genetically related radionuclides. The table presents a list of parent-daughter pairs which have been suggested for studies on secular or transient equilibrium.
A lead absorber of 520 mg/cm2 was used to absorb most of the radiations from Cel" while transmitting appreciable intensities of the PrlA4y-rays. Methyl isobutyl ketone (hexone) was chosen as the solvent for this study. The distribution coefficient for Ce(1V) is considerably greater than that for Pr(111) under the conditions outlined; therefore, a clean single-stage separation is effected. Other systems may be used for educational variety: e.g., tri-nhutyl phosphate in inert hydrocarbon diluent (I.$), acetylacetone in CC14 (15), or thenoyltrifluoroacetone in xylene (16).
-
Parent-Dauahter Pairs for Eauilibrium Studies Related pan Bs"O-La240 Cal"-Bal"
BimrpbBor Th*,'-Pa'fi
Half-life of ~ s r e n t 12.8 da
'0.0 y i 8.0yr
224.10 da
Ce14cPr14* 290.0 d s Pb"'-Bil'> 10.04 ihr
Half-life of daughter
Suggested mode of separatmn
40.2 hr 2.00 min
Ion exchange Ionexchange Precipitation I O emhaage ~ , Colloid adsorptmn Solvent extraction Precipitation Eleotrolysis
0.84 seo 1.17 min 17.5 min 80.5 min
~
o
I
v
~
~
Ref.
I3
(80)
(7)
(8) (9) (3. 10) (11) ~ (1s) ~ x
The Experiment ~
The purpose of this paper is to present an experiment in which the data can he obtained in a three-hour period; to suggest solvent extraction as a rapid and simple method of separating from Pr'44; to suggest the use of count rate meter and recorder, if available, as substitutes for a scaler; and to point out several features in the treatment of data. The following decay scheme (IS) is pertinent to this experiment :
-
Ce'" 290 dam
S- 0.304 (72%)
0.17 (22%) 0.223 ( 4 3%)
P P * 17.5 minutes Nd'" 2 2 A
8- 2.98 (97%)
loL6yr.
___)
(stable)
2.28 (1%) 0 . 8 (2%)
~
~
c
~
~
o
~
A stock aqueous solution of about 1 pc Ce144-Pr144/ ml is macie 3 M in HNO1. A small volume (1-3 ml) of the stock solution is transferred to a separatory funnel. Approximately 200 mg solid sodium bismuthate is added to oxidize Ce(II1) to Ce(1V). An equal volume of hexone is added. The funnel is shaken for one minute. Separation of phases occurs rapidly. The time when the phases separate is noted. About 10 drops of the organic phase, containing Cel",are transferred to a planchet, and several drops of dilute collodion are added. The sample is dried rapidly under a heat lamp. Total elapsed time between separation of phases and counting can be reduced to less than two minutes. Data ohtained with a Radiation Counter Laboratory Geiger detector and scaler setup are plotted in Figure 1,
8:
and y-ray energies are given in Mev. p r a y intensities are given as percentages (based on the fraction of total disintegrations of the nuclide). The parenthetical terms following the y-ray energies are relative intensity values. The growth of Prld4 is followed in the fraction containing initially pure Ce'"'. A study of the decay scheme indicates that discrimination in counting will improve the quality of the data. Both CeI4&and Prlh4 have mixed beta-gamma spectra, and it is desirable in this experiment to count Pr14' selectively. In an advanced course, a gamma spectrometer may be used. In many laboratories, only Geiger detectors and scalers are available. In that case, discrimination may often be effected by use of absorbers. A more sophisticated experiment would use a count-rate meter and recorder in place of the scaler. The data presented in this paper were obtained using a Geiger tube detector with a scaler, for the first set, and with a
~ i ~ w e z lData . obtained b y Geiger detestor and ~ a l e r . Letters la) total activity of initially pure Ce"' (bl decoy of PrI4'i (c) saturation activity of Ce"' Pr'"; (dl Cel" activity. reprelenh
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Volume 42, Number 8,
August 1965
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427
curve a. Points are plotted every two minutes, each point representing a one-minute count starting 30 seconds before the plotted time. Background has been subtracted. A similar set of data was obtained by using a Geiger detector, Baird Atomic count rate meter, and recorder. Figure 2 is a plot of points taken from a smooth curve drawn through the recorder trace. The fit of this plot indicates that the inherent randomness of counting has been averaged by the count rate meter.
(4) FRIEDLANDER, G., KENNEDY, J. W.,
AND MILLER,J . M., "Nuclear and Radiochemistry," 2nd ed., John Wiley and Sons, Inc., New York, 1964, pp. 73-75. C. D., J . CAEM.EDUC.,32, (5) KRUGER,P., AND CORYELL,
280 (1955). (6) HAYES,R. L., AND BUTLER,W. R., JR., J. CHEM.EDUC., 37.590(1960>. -. - - - ~ - - - - , ( 6 4 CHOPPIN,G. R., AND NEALY,C. L., J. CHEM.EDUC.41, 598 (1964). (7) JONES,W. H., J. CHEM.EDUC.,34, 406 (1957). (8) BOOTH,A. H., J. CHEM.EDUC.,28, 144 (1951). D. J., AND LAWRENCE, J. J., J. CHEM.EDUC., (9) CARSWELL, 36. 499 (1959). A., ADAMOWICZ, M., J. CHEM.EDUC.,36, (10) 136 (1959). (11) DILLARD,C. R., AND MORTON,L., J. CHEM.EDUC.,35, 23R --- (19581~ \----,. (12) PAREKH,P. P., AND DAS, M. S., J. CHEM.EDUC.,40, 354 (1963). W. H., "Trilinear Chart of Nuclides," US. (13) SULLIVAN, Atomic Energy Commission, 1957. S., AND WYMER,R. G., "Chemistry in Nuclear (14) PETERSON,
.
BRADLEY,
AND
Technology," Addison-Wesley Publishing Company, Inc., Reading, .Mass. 1963, pp. 108, 109. R. R., AND CORYELL,C. D., "Brookhaven Na(15) EDWARDS, tional Laboratory Conference on Chemical Effects of Nuclear Transformations," AECU-50, (BNGG7), 52-62 (1948). C. V., Anal. Chem., 35,1887 (1963). (16) ONISHI,H., AND BANKS,
2 0 ~
20
40
60
80
100
120
TIME (mi01
Data for la) obtained from recorder trace of count rate meter. Notation is identical to thot far Figure 1.
Figure 2.
The following is pertinent to both Figures 1 and 2: Curve a is the con~posite and Pr'44 activity. Curve a is subtracted from the extrapolated value of the saturation level c to give curve b, the decay curve of PrlP4,from which the half-life can be determined. The best statistical values for determining curve b fall between -30-70% saturation. The intercept of curve b on bhe ordinate is the saturation activity of Pr144. Curve d is the approxin~atevalue of the activity of Ce144,and it is the difference between the saturation activity of Pr14' and the total saturation activity. The value for the Celd4activity can be determined by extrapolation of curve a, but with much less credence due to the greater statistical error associated with the iuit,ial count,ing periods. The actual disintegration rates of Ce"' and Pr144are equal a t saturation; the student should calculate the ratio of detection coefficients for Ce'44and Pri4' for his counting setup. Literature Cited (1) HARVEY,B. G., "Introduction to Nuclear Physics and
Chemistry," Prentice-Hall, Inc., Englewood Cliffs, N. J., 1962, pp. 35-37. (2) CHOPPIN,G. R., "Experimental Nucless Chemistry," Prentic~Hall,Inc., Englewood Cliffs, N. J., 1961, pp.
.
114.86. - - ~ (3) OVERMAN, R. T., AND CLARK,H. ~
M., "Radioieotope Techniques," MoGraw-Hill Book Company, Inc., New York, 1960, pp. 305-310, 333-336.
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