The Rediations Emitted from Artificially Produced Radioactive Substances. II. The Gamma-Rays from Several Elements

A method for measuring the energy and relative intensity of the gamma-rays emitted by light radioactive elements is discussed. It depends upon the measurement of the momentum distribution of the Compton recoil electrons projected from a thin mica radiator situated in a cloud chamber traversed by a magnetic field. In the energy range from 0.5 to 5 Mev the distribution includes only those electrons whose initial velocity makes an angle of less than 10° with the path of the incident gamma-ray. The theoretical distribution curves indicate an average expected half-width of about 250 kv. Experimental data have been obtained which completely validate the theory. The gamma-radiations from ${\mathrm{A}}^{41}$, ${\mathrm{Na}}^{24}$ and ${\mathrm{N}}^{13}$ have been investigated by this method. The argon radiation appears to be monochromatic with an energy of 1.37 Mev. Sodium emits three lines at 0.95, 1.93 and 3.08 Mev which are possibly interrelated. Also the two quanta annihilation radiation from the positrons of radio nitrogen was checked at 0.51 Mev. The results indicate that the method is quite satisfactory in the energy range from 0.5 to 3 Mev.