Measurements in pulsed BeO assemblies with decay constants in the region of Corngold's limit.

Abstract

Decay curves have been measured in BeO assemblies with bucklings in the range 1.93 x 10 -2 cm-2 to 5.34 x 10 -2 cm-2 at times from immediately after the initial pulse to at least 4.5 ms after the pulse. The decay curves for assemblies with B2 < 2.91 x 10 -2 cm-2 can be described by an exponential, from a minimum of 1.5 ms after the pulse to greater than 3.0 ms after the pulse. For bucklings greater than B2 = 3.3 x 10 -2 cm-2 the decay curves cannot be described by an exponential in this time region, and the departure from exponential increases with increased buckling. The results indicate a transition region at B2 ~ 3.0 x 10 -2 cm-2, (λ ~ 3.65 x 10 3 sec-1) which is consistent with the expression proposed by Kothari for the upper limit on discrete decay constants and well above Corngold's limit of λ* = (υΣinel) min ~ 2.5 x 10 3 sec-1. The transition point does not have any marked shape dependence. There is some shape dependence in the behaviour of decay curves for assemblies with B2 > 3.3 x 10 -2 cm-2 but little dependence of pulse length, or counter shape and position.