Precise measurement of energy of the first excited state of 115Sn (Eexc ≃ 497.3 keV)

Single beta decay of In-115 to the first excited level of Sn-115 (E-exc similar or equal to 497.3 keV) is known as beta-decay with the lowest Q(beta) value. To determine the Q(beta) precisely, one has to measure very accurately the Eexc value. A sample of tin enriched in Sn-115 to 50.7% was irradiated by a proton beam at the U-120 accelerator of INR, Kyiv. The Sb-115 radioactive isotope, created in the Sn-115(p,n)Sb-115 reaction, decays with T-1/2 = 32 min to Sn-115 populating the 497 keV level with similar or equal to 96% probability. The total statistics of similar to 10(5) counts collected in the 497 keV peak in a series of measurements, the exact description of the peak shape and the precisely known calibration points around the 497 keV peak allowed to obtain the value Eexc = 497.342(3) keV, which is the most precise to-date. This leads to the following Q*(beta) value for the decay In-115 -> Sn-115*: Q*(beta) = 147 +/- 10 eV. Copyright (C) EPLA, 2018