Measurement of the Energy of a Beta-Ray of Radium B

The energy of the most intense beta-ray line from radium B has been measured and found to be 2.6145×{}10⁵ electron-volts, taking e/m to be 1.760×{}10⁷ e.m.u. per gram. The value of Hρ for this line was found to be 1931.8 gauss cm. The spectrum was obtained by the magnetic focussing method and the magnetic field was measured by the Cotton balance method. All measurements were made to within one part in ten thousand and it is hoped that the error in Hρ is not greater than this. The value for the energy of course depends on the value of e/m and hence may be in error by about one part in one thousand.