A Precise Momentum Measurement of theFLine of Thorium B

Abstract
The momentum of the internal conversion electrons of the F line of thorium B has been compared with the momentum of electrons accelerated through a known potential difference. The comparison was made by means of an iron-free high-resolution solenoidal magnetic field beta-ray spectrometer. The value obtained for the F line is 1388.56±0.21 gauss-cm. Other useful calibration lines following the decay of thorium B have also been measured by comparison with the F line.