The operation of a low energy Beta ray spectrometer and the measurement of the spectrum of radium D

A semicircular focussing spectrometer has been built to examine beta spectra in the energy range below 100 Kev. The detection of the beta particles is accomplished by means of Geiger counters filled with the saturated vapor of liquid heptane (C₇H₁₆) kept in a bath of melting ice. The windows of the counters are made from thin films of zapon about 5 to 8 micrograms/cm² in thickness. The sources are mounted on similar films approximately 10 micrograms/cm² and have an average total thickness of the order of 30 micrograms/cm² . The combination of thin source and thin windows enables measurements of spectra to be made down to an energy of 2 Kev. An examination of the beta spectrum of RaD (₈₂Pb²¹⁰) with the spectrometer has been carried out. It consists of L, M and N conversion lines of a 47 Kev. gamma ray, a peak at about 3 Kev assigned to conversion of a 7.7 Kev gamma in the M shell of the atom, and a primary beta spectrum. A Kurie plot of the primary beta spectrum yields an end point of 21.7 Kev. In addition there are two weak conversion lines at 18 and 21 Kev which are tentatively assigned to the L conversion of gamma rays of 34 and 37 Kev.Science, Faculty ofPhysics and Astronomy, Department ofGraduat