JOSHI EFFECT IN BENZENE VAPOUR UNDER X-RAYS. PART I. INFLUENCE OF EXCITING POTENTIAL

Joshi effect in benzene vapour under X-rays, in an ozoniser discharge, is studied due to 50 cycle potentials in the range 7—20 kV. The range of potential (V) studied consists of (a) 0-7.4 kV i e. well below Vm, the 'threshold potential' (8 kV), the current being capacitative and unaffected by X-rays ; (b) 7.4-7.96 kV where the discharge is not 'self maintained', a large reversible positive Joshi effect is observed; (c) a narrow region 7.95-7.68 kV characterised by an irreversible + Δi ; (d) a region of 'self-maintained' discharge 8-20 kV wherein — % Δi, maximum near Vm is observed The results are explained by an extension of Joshi's theory associating — Δi with the space charge effect due to negative ions, to a consideration of the behaviour of the positive ionic space charge.