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.
X-ray equipment, used for radiation therapy at low voltages, is frequently operated in small hospitals which do not have full-time physics staff. Most of the X-ray units involved are not fitted with dose-rate monitors which would allow continuous control dose so that the output must be checked at frequent intervals by the radiographer using a suitable instrument. The design criteria for such an instrument are discussed and its construction described in detail together with the tests and field trials carried out. The instrument is designed to measure dose rates from 2500 rad min-1 at 10 kV to 50 rad min-1 at 250 kV. It has been possible by use of the instrument to determine the 'normal' behaviour of each X-ray unit and to establish criteria by which 'abnormal' behaviour can be determined.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.