2 - ENERGY MEASUREMENTS WITH PROPORTIONAL COUNTERS

Abstract

This chapter discusses energy measurements done using proportional counters. The method of measuring the energy of a charged particle by means of the total amount of ionization it produces in coming to rest is well established in nuclear physics. Proportional counters have been used for a long time in nuclear research, but it was only comparatively recently that their full potentialities for measuring energies below the range of the pulse ionization chamber were first appreciated. The method opens up a field of investigation into low-energy phenomena, many of which could previously be studied only indirectly or by means of more involved techniques. In addition to the study of low energy β -ray spectra, where the overriding merit of the proportional counter is that it allows the use of a gaseous source, it has also proved very useful in the study of nuclear gamma rays in the energy region up to 100 kev or more. Characteristic X-rays excited by nuclear phenomena, nuclear gamma rays, and low-energy conversion electrons can be studied and their energies measured to a degree of precision that is often better than that obtained by means of magnetic β -ray spectrometers at these energies. The accuracy, of course, does not compare with that attained by crystal diffraction methods, but the source strength required is very much smaller.