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Intm'mttional Journal of Applied Radiation and ~
1976, Vol. 27, pp. 613--614. Pm]pemoa Press. Printed in Northma Ireland
The Half-Life of 1'9'Sn G. C. MARTIN, JR. General Electric Company, Vallecitos Nuclear Center, Pleasanton, CA 94566, U.K. The half-life of 119mSn was measured over a period of 3.6 years and found to be 293.0m 1.3 days, the quoted counting error being at the 95% confidence level.
INTRODUCTION IT IS apparent from available 119mSn half-life measurement data in the literature (x-2) and from the increasing use of this radionuclide for M6ssbauer studies, that a more definitive value of the half-life is desired. Studies at our laboratory of lX9mSu product have indicated that the published half-life values of approximately 250days ~1) and 245±20days <2~ are somewhat too short. In this work, a determination of the isomeric half-life of 119mSn from intensity measurements of the 23.9 keV v-ray and approximately 25 to 30 keV X-rays was made at various times over a period of time equivalent to approximately 4.5 halflives. A source of x19'Sn activity was prepared in the General Electric Test Reactor (GETR) by the 6-month irradiation of SnO2 enriched to 96.6% ltSSn. The SnO2 was obtained from the Oak Ridge National Laboratory (ORNL). After cooling 16 months, followed by a chemical separation of tin from antimony and indium, all interfering nuclides (125Sn, 117'Sn, 114m In, 1 2 5 m Te, 1 2 4 Sb, 1 2 5 Sb) other than 113 Sn, either had decayed or were removed. The decay or removal of the interfering nuclides was verified by counting the separated sample with both Si(Li) and Ge(Li) detector systems. A source for half-life analysis was prepared by a SnS2 precipitation, the source of activity occupying a 2-cm-dia. circle. A 113Sn source was prepared similarly by a 6-month irradiation of ORNL-supplied SnO2 enriched to 79.6% 112Sn, followed by the purification, precipitation, and mounting of a 2-cm-dia. source.
30-cm source-to-detector distance with a 7.6cm x7.6-cm NaI(TI) detector in conjunction with a 1024-channel analyzer at a gain of 0.8 keV/ch, with discrimination limits of 15 and 38 keV. The photopeak pulse-height distribution was summed and corrected for background and for U3Sn interference. The background initial contribution was 0.01% and increased to 0.36% at 3.6 years. Counts were taken in duplicate on each day of measurement. The average of the duplicate counts constituted a measurement for that day [the average ratio of 32 duplicate counts was 1.0026m0.0017(l~r)]. Count times varied from 200 sec initially to 1400 sec with gross counts ranging from 4 x 105 to 1 x 105, respectively. Count rates were low (<5000cps) making dead-time corrections unnecessary. Constant geometry for the source-detector arrangement was employed and verified for each measurement by counting, also in duplicate, a 25/~Ci 2 4 1 A r n 2-cIn source and summing the 15 to 72 keV region. This 241Am source was t
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~' & & & ,'~ ,2~ ,co Time, days PROCEDURE A N D RESULTS FIo. 1. The 24-30 keV photon photopeak inThe intensity of the 24 to 30 keV photons tensity as a junction of time (in days) from the was determined by counting the t19mSn at a beginning of the measurement. 2 613
614
G. C. Martin, Jr.
appropriately corrected for decay throughout the 3.6-year measurement. The 115 day H3Sn radionuelide initial contribution to the 24- to 30-keV photopeak count rate of the 119mSn source was 1.3% and decreased to less than 0.2% after 2 years. This interference was determined by counting the purified 1138n source 13 times over a period of 2 years and a count-ratio of 1.50+0.02(lcr) for the 24 to 30 keV photopeak vs the 392 keV photopeak was obtained. This ratio was applied to each 119'Sn measurement and the 392 keV photopeak was measured until it could no longer be observed, 2.5 years after the initial count. A decay curve was obtained from 32 measurements of the 119mSn photopeak intensity for which measurements extended for 3.6 years. The corrected values vs time and the best fit for the isomeric half-life by the leastsquares method is shown in Fig. 1. The values
of the half-life obtained by least-squares fitting and estimated counting error were 7'1/2= 293.0+ 1.3 days,
for a confidence level of 95%. The uncertainty given is the standard error multiplied by a Student factor for 30 degrees of freedom. All measurements were weighted equally in the least-squares fitting. Acknowledgement--The author wishes to thank Mr. J. P. PETERSON for the radiochemical separation of the tin activities and Mr. C. L. PETERSON for the error analysis.
REFERENCES 1. MnCaLXCHJ. W. and HILL R. D. Phys. Rev. 79, 781 (1950). 2. NELSON C. M. KI~TELLEB. H. and BOYD G. E. Studies on the Nuclear Chemistry of Tin. ORNL828 (1950).

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  • . The half-life is the time it takes for half of the original sample of radioactive material to decay to half its original. Radioactive Half- Life. Most radioactive materials decay in a series of reactions. Radon gas comes from the decay of uranium in the soil.
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