Metastable and charged particle decay in neon afterglow studied by the breakdown time delay measurements

Abstract

Memory effect—the long time variation of the electrical breakdown time delay on the relaxation time td¯(τ) in neon—was explained by the Ne(P23) (1s5) metastable state remaining from the preceding glow [Dj. A. Bošan, M. K. Radović, and Dj. M. Krmpotić, J. Phys. D 19, 2343 (1986)]. However, the authors neglected the quenching processes that reduce the effective lifetime of metastable states several orders of magnitude below that of the memory effect observations. In this paper the time delay measurements were carried out in neon at the pressure of 6.6mbar in a gas tube with gold-plated copper cathode, and the approximate and exact numerical models are developed in order to study the metastable and charged particle decay in afterglow. It was found that the metastable hypothesis completely failed to explain the afterglow kinetics, which is governed by the decay of molecular neon ions and molecular nitrogen ions produced in Ne2+ collisions with nitrogen impurities; i.e., Ne2++N2→N2++2Ne. Charged particle decay is followed up to hundreds of milliseconds in afterglow, from ambipolar to the free diffusion limit. After that, the late afterglow kinetics in neon can be explained by the nitrogen atoms recombining on the cathode surface and providing secondary electrons that determine the breakdown time delay down to the cosmic rays and natural radioactivity level.