Measurement of the radiations from 131I and 131Xe∗ with a lens type beta-ray spectrometer

Abstract

A description is given of the construction of a lens type spectrometer with an annular exit slit. An experimental method for the adjustment of this slit is described. The instrument has a transmission of one per cent. and a line width of 2, 3 or 4 per cent for sources of 3, 6 or 9 mm diameter. The influence of radiator thickness on the shape of photoelectron lines has been studied. The beta and gamma ray spectra of 8.0 d 131I have been investigated as well as the conversion spectrum of 131Xe∗. Photoelectrons ejected from Pb and U by gamma rays of 80, 284, 364 and 636.5 k eV have been found. Internal conversion electrons from all these gamma rays are present. In sources which have aged for some days also conversion electrons from the 163 k eV gamma ray of 12 d 131Xe∗ appear. These conversion electrons have also been observed in the conversion spectrum of Xe gas extracted from a 131I sample. In the beta spectrum of 131I two components of maximum energies 606 and 334 k eV are easily found, both yielding straight Kurie plots. In addition a very weak third component has been detected which is assumed to lead to the metastable Xe level. Also a very weak internal conversion line is found at 690 k eV corresponding to a hitherto unknown gamma ray of 724 k eV. The level scheme of Metzger and Deutsch is confirmed. A consistent spin and parity assignment to the levels is possible, the 606 k eV beta transition being allowed despite its high ft-value of 4.5 × 10 6.