Ionisation chamber - partic. for measuring photon activity from a tritiated target

摘要

Ionisation chamber comprises (a) a first hemispherical electrode with a vertical axis placed under high tension by a stabilised potential source, wholly surrounded by a metal casing filled with an ionisable gas; (b) a second collector electrode with the same axis as the first, of greater thickness than the mean free path of absorption of beta-radiation emitted by the source in the material of this electrode, which is fixed to the casing to form in association therewith a sealed enclosure filled with ionisable gas; (c) a metal rod element inserted in an opening in the casing for bringing the source from the interior of the external volume to the chamber, delimited by the second electrode. The source is situated on the axis of the first and second electrodes at a point such that the geometry of the electrodes constitutes a counter 3 pi steradians. In addn. this metal rod adjusted in the opening of the casing completes the electrical screening to earth of the chamber formed by the casing and rod; and (d) means for measuring the current collected by the second electrode which pref. is of hemispherical shape or is a cylinder capped by a cone section. Design enables the intensity of photon emission from a radiographic source to be determined, while excluding the effect of beta radiation. Partic. for measuring the activity of tritiated targets.