Two Windowless Chambers for the Measurement of Grenz Rays

Abstract

The large amounts of soft radiation in the spectrum of a beryllium window X-ray tube operated in the grenz-ray region, and the high exposure rates used, necessitate a measuring chamber of special design. Two chambers of unusual design (described at an I.A.E.A. Symposium in 1960) have now been in use for seven years for this purpose. This paper describes them briefly, their subsequent performance, and the modifications made to one of them. Chamber 1 is of robust construction, its two electrode supports being half-cylinders of Perspex with the flat faces opposing each other at a separation of 6 mm. One face is graphited completely and is connected to a voltage of 300 V; the other face has a central region roughly 1 cm in diameter forming the collecting electrode and is surrounded by a guard ring at zero potential covering the remainder of the face, each electrode being formed by graphite on the Perspex surface. The chamber is shown in Fig. 1. It is a free-air chamber, readily portable and used in conjunction with an E.I.L. (E.F.37A) electrometer.