Comparative analysis of spectra of the background of the proportional counter filled with Kr, enriched in Kr-78, and with Kr of natural content

The results of the experiment searching for 2K-capture with large low-background proportional counter are presented. The comparison of spectra of the background of the proportional counter filled with Kr enriched in ${}^{78}$Kr (8400 hr) and with natural Kr (3039 hr) is given. A new limit on the half-life of ${}^{78}$Kr with regard to 2K-capture, T${}_{1\mathrm{/}2}\ge 2.0\cdot {10}^{21}$ yrs (95% C.L.) has been obtained.