An ion pulse ionization chamber for spectrometric measurements of low surface α activities

The design of a pulse ionization chamber for measuring the surface αactivity of various samples is described. When used together with the appropriate methods for recording and processing the signals, a low-background spectrometer based on this chamber is able to ensure a high sensitivity in direct measurements of ultralow surface α activities. This approach offers a solution to the problem of controlling superpure materials used in detectors for studying rare nuclear processes with a broken equilibrium in the decay chains of the uranium and thorium series. A procedure for modeling the shape of the current pulses according to the orientation of α-particle tracks and their location inside the chamber is described. Results obtained with an α source, as well as with copper and VM2000 light-reflecting film samples, are presented.