On the absorption of homogeneous β-rays by matter, and on the variation of the absorption of the rays with velocity

The present work was undertaken with a view to establishing, if possible, the connection between the absorption and velocity of the β-rays. So far, no actual experiments have been performed on this subject, but Schmidt has determined the velocity of the rays emitted by radium E and uranium X. These have absorption constants of 40 cm.-1 and 14 cm.-1 , and their velocities, assuming the Lorentz formula for the variation ofe/m with velocity of an electron, are 2.31 and 2.76 x 1010 cm. per sec. respectively. The matter has been attacked theoretically by Sir J. J. Thomson. He deduces a formula connecting the "diffusion" coefficient of absorption with the velocity, and finds that the variation takes place inversely as the fourth power of the velocity. Seitz has made a series of experiments on the number of cathode particles passing through thin sheets of matter, and finds the coefficient of absorption to vary inversely asav 6 –bv 4 , wherea andb are constants andv the velocity of the electrons.