Under bombardment by 3.3 MEV deuterons, magnesium becomes radioactive with the emission of negative electrons and gamma-rays, and with two decay periods: 10¼±¼ min. and 15.8±0.5 hours. These periods are characteristic of ${\mathrm{Mg}}^{27}$ (Fermi) and ${\mathrm{Na}}^{24}$ (Lawrence). The reactions producing these bodies are: $\{{}_{12}{}^{}{}_{}{}^{}\mathrm{Mg}_{}^{26}{}_{}{}^{}+{}_1{}^{}{}_{}{}^{}\mathrm{H}_{}^2{}_{}{}^{},={}_{12}{}^{}{}_{}{}^{}\mathrm{Mg}_{}^{27}{}_{}{}^{}+{}_1{}^{}{}_{}{}^{}\mathrm{H}_{}^1{}_{}{}^{}; {}_{12}{}^{}{}_{}{}^{}\mathrm{Mg}_{}^{27}{}_{}{}^{}={}_{13}{}^{}{}_{}{}^{}\mathrm{Al}_{}^{27}{}_{}{}^{}+\beta +\gamma .\}\{{}_{12}{}^{}{}_{}{}^{}\mathrm{Mg}_{}^{26}{}_{}{}^{}+{}_1{}^{}{}_{}{}^{}\mathrm{H}_{}^2{}_{}{}^{},={}_{11}{}^{}{}_{}{}^{}\mathrm{Na}_{}^{24}{}_{}{}^{}+{}_2{}^{}{}_{}{}^{}\mathrm{He}_{}^4{}_{}{}^{}; {}_{11}{}^{}{}_{}{}^{}\mathrm{Na}_{}^{24}{}_{}{}^{}={}_{12}{}^{}{}_{}{}^{}\mathrm{Mg}_{}^{24}{}_{}{}^{}+\beta +\gamma .\}$ The protons have not been looked for. The alpha-particles have a range of about 7 cm. The ${\mathrm{Mg}}^{27}$ beta-rays have 2.0 MEV maximum energy, and the accompanying hard gamma-ray has about 1.3 MEV energy. The voltage excitation functions of these two activities have been measured, and have been found to follow different laws. The ${\mathrm{Mg}}^{27}$ following the Oppenheimer and Phillips function and the ${\mathrm{Na}}^{24}$ the older Gamow function. At 3 MEV one atom becomes ${\mathrm{Na}}^{24}$ for each 9.6 atoms going to ${\mathrm{Mg}}^{27}$. The thick target yield of ${\mathrm{Mg}}^{27}$ atoms is about 5 per ${10}^7$ deuterons. The nuclear cross section (${\mathrm{Mg}}^{26}$) at 3 MEV is about 2.4×${10}^{-26\mathrm{}}$.

• Received 16 September 1935

DOI:https://doi.org/10.1103/PhysRev.48.855