An Ionization Chamber Study of Electron and Ion Decay in Irradiated Ammonia

Abstract

Ionization chambers with plane parallel and coaxial electrodes have been used to study the ion and electron concentrations in ammonia subjected to 120 kvp X-ray pulses of 17 and 30 ms duration. Differences in the numbers of positive and negative ions collected on the application of pulses of high voltage imply that free diffusion of electrons to the cell walls occurs in the early part of the X-ray pulse until it is inhibited by the positive ion space charge. Thereafter, positive and negative ions decay at equal rates.The rate constant for the neutralization reaction[Formula: see text]at 1200 Torr of ammonia and 297°K was calculated to be 4.2 ± 1.0 × 10−5 cm3 ion−1 s−1. However, unless extensive precautions are taken to remove electron-attaching impurities reactions between NH4+•nNH3 ions and impurity negative ions are dominant. The results are discussed and compared to other work on electron–ion neutralization reactions.

The onset of diffusion control for ion-ion neutralization in ammonia vapor

“…Procedures for baking and filling the chamber, which was fitted with a grease-free stopcock, were the same as those used before. 24,27 At pressures of 25 torr and above ions were produced by exposing the ionization chamber to repetitive pulses of X rays generated by stopping electrons from a 1.5-MeV high-voltage Engineering Corporation van de Graaff accelerator in a 0.3-cm thick water-cooled gold target. The pulse frequency, v, and the pulse width were varied over the ranges 15-25 s'1 and 50-250 µß, respectively.…”