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

TL;DR

This paper reports a highly precise measurement of the first excited state energy of 115Sn at 497.342 keV, enabling a more accurate determination of the beta decay Q value with implications for nuclear physics.

Contribution

The study provides the most precise measurement to date of the 115Sn first excited state energy, improving the accuracy of the beta decay Q value for 115In.

Findings

Excited state energy measured as 497.342(3) keV

Q* value for decay determined as 147 ± 10 eV

Enhanced precision in nuclear energy level data

Abstract

Single beta decay of 115In to the first excited level of 115Sn (Eexc = 497.3 keV) is known as beta decay with the lowest Q value. To determine the Q precisely, one has to measure very accurately the Eexc value. A sample of tin enriched in 115Sn to 50.7% was irradiated by proton beam at the U-120 accelerator of INR, Kyiv. The 115Sb radioactive isotope, created in 115Sn(p,n)115Sb reaction, decays with T1/2 = 32 min to 115Sn populating the 497 keV level with ~ 96% probability. The total statistics of ~ 10^5 counts collected in the 497 keV peak in series of measurements, exact description of the peak shape and 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* value for the decay 115In to 115Sn*: Q* = 147 +- 10 eV.