Comparative study of the double $K$-shell-vacancy production in single- and double-electron capture decay

TL;DR

This study compares double K-shell vacancy production in single and double electron capture decays of krypton isotopes, measuring probabilities, signal-to-background ratios, and half-lives to better understand decay mechanisms.

Contribution

It provides the first measurement of the probability of double K-shell vacancy production in $^{81}$Kr decay and a detailed analysis of decay signals in $^{78}$Kr, advancing knowledge of electron capture processes.

Findings

Measured $P_{KK}=(5.7 ext{±}0.8)×10^{-5}$ for $^{81}$Kr decay.

Determined the half-life of $^{78}$Kr double electron capture as approximately $1.9×10^{22}$ years.

Achieved a signal-to-background ratio of 15/1 for $^{78}$Kr decay analysis.

Abstract

We carried out the comparative study of the signal from the decay of double $K$-shell vacancy production that follows after single $K$-shell electron capture of $^{81}$Kr and double $K$-shell electron capture of $^{78}$Kr. The radiative decay of a the double $1s$ vacancy state was identified by detecting the triple coincidence of two $K$ X-rays and several Auger electrons in the $ECEC$-decay, or by detecting two $K$ X-rays and (Auger electrons + ejected $K$-shell electron) in the $EC$ decay. The number of $K$-shell vacancies per the $K$-electron capture, produced as a result of the shake-off process, has been measured for the decay of $^{81}$Kr. The probability for this decay was found to be $P_{KK}=(5.7\pm0.8)\times10^{-5}$ with a systematic error of $(\Delta P_{KK})_{syst}=\pm0.4 \times10^{-5}$. For the $^{78}{\rm{Kr}}(2\nu2K)$ decay, the comparative study of single- and double-capture decays allowed us to obtain the signal-to-background ratio to be 15/1. The half-life $T_{1/2}^{2\nu2K}(g.s. \rightarrow g.s.) = [1.9^{+1.3}_{-0.7}(stat)\pm0.3(syst)]\times 10^{22}$ y is determined from the analysis of data that have been accumulated over 782 days of live measurements in the experiment that used samples consisted of 170.6 g of $^{78}$Kr.