The Continuous X-Rays Excited by the Beta-Particles ofP3215

The internal and external x-rays (innere and äussere bremsstrahlung) excited by the beta-particles of ${}_{15}{}^{}{}_{}{}^{}\mathrm{P}_{}^{32}{}_{}{}^{}$ were investigated by means of a Freon-filled ionization chamber connected to a sensitive d.c. amplifier. The intensity of the internal x-rays excited by the disintegration electrons when leaving the nucleus was found by the extrapolation method to be approximately equal to one-fourth of that of external x-rays excited by completely stopping the electrons in aluminum. From the experimental data the total energies of the two radiations were estimated. For internal x-rays this estimate leads to about $0.0020 m{c}^2$ per disintegration electron, and for the external x-rays excited in aluminum to about $0.0082 m{c}^2$. On the other hand, by making use of Lyman's magnetic beta-spectrum of ${}_{15}{}^{}{}_{}{}^{}\mathrm{P}_{}^{32}{}_{}{}^{}$ the energy of internal x-rays calculated from the theory of Knipp and Uhlenbeck was $0.0020 m{c}^2$ per disintegration electron and the energy of the external x-rays expected from the theory of Bethe and Heitler was $0.0089 m{c}^2$. Therefore the experimental results are in good accord with the theoretical predictions. The relation between the intensity of the external x-rays excited by completely stopping electrons in Pb, W, Sn, Ag, Mo, Cu, Fe, Al, C and Be and the atomic number was investigated. It was found to be in fairly good agreement with the theoretical curve derived according to Bloch's formula for energy loss of electrons by inelastic collisions (F. Bloch, Ann. d. Physik 16, 285 (1933); Zeits. f. Physik 81, 363 (1933)) and the theory of Bethe and Heitler, namely that the intensity is proportional to the square of the atomic number. From the shape of the absorption curves of the total x-rays it will be seen that the spectral distribution of the external x-rays is independent of $Z$ (atomic number) and is also approximately the same as that of the internal x-rays.