Abstract
Simultaneous measurements of small ionization currents I and formative time lags tf in uniform electric fields E have been made for spectro-scopically pure hydrogen at pressures p0 (< 15 mmHg) between plane parallel gold surfaces in the range 56 < Es/p0 < 170 v cm-1 mmHg-1 dagger over which the observed growth times lay between 10-6 and 10-4 sec for an over-voltage up to approximately 3% in excess of the static sparking potential Vs. In this time range the currents increased from about 10-9 A to about 10-4 A and the early stages of growth, approximately 10-9 < I ≲ 10-5 A, were found to be described by an expression of the form I = A + B exp(λt) in agreement with Davidson's analysis. The growth constant λ and hence the relative importance of the secondary ionization processes responsible for growth were evaluated directly from the current measurements and are tabulated for the whole range studied. Estimates of the photoelectric yield, k similar 10-2 electrons per quantum, are deduced: these are in agreement with directly measured values.