Investigating 2K-capture in 78Kr with a large-volume copper proportional counter
A component analysis of the background of a copper proportional counter with allowance for its input to the parametric region of events due to the expected 2K-capture in 78Kr is presented. The technique of discriminating the simulated events on the edges of the working length of the anode wire is described by comparing the pulse amplitudes of the sought pulse and the first afterpulse in a detector filled with pure krypton without quenchers. The limit on 2K(2ν)-capture for the ground state 78Se (0+ → 0+, g.s.) was found to be T1/2 ≥ 2.4 × 1021 yr (90% confidence level).