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

Single beta decay of 115 In to the first excited level of 115 Sn ( ) is known as β -decay with the lowest value. To determine the precisely, one has to measure very accurately the value. A sample of tin enriched in 115 Sn to 50.7% was irradiated by a proton beam at the U-120 accelerator of INR, Kyiv. The 115 Sb radioactive isotope, created in the 115 Sn(p,n)115 Sb reaction, decays with to 115 Sn populating the 497 keV level with probability. The total statistics of 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 , which is the most precise to-date. This leads to the following value for the decay 115 In → 115 Sn* : .