Simultaneous alpha-particle bombardments of ${\mathrm{Ge}}^{70}$, enriched electromagnetically to 90 percent, and germanium of normal isotopic constituency have established the location of an arsenic activity of 76±3 days' half-life at mass number 73. Decay is by $K$-capture into ${\mathrm{Ge}}^{73}$. The energy of the gamma-ray is about 0.10 Mev. The half-life of ${\mathrm{As}}^{74}$, measured over 10 half-lives, is 17.5±0.1 days. Simultaneous deuteron bombardments of two selenium samples, enriched, respectively, in isotope 74 and 76, have established the location of the 1.08-day arsenic activity at mass number 72. A radioactive arsenic isotope of 2.08 days' half-life has been produced by deuteron bombardment of germanium and is assigned to ${\mathrm{As}}^{71}$.

• Received 4 August 1948

DOI:https://doi.org/10.1103/PhysRev.74.1315