Argon has been irradiated and ${\mathrm{Cl}}^{39}$ produced by the reaction ${\mathrm{A}}^{40}(\gamma ,p){\mathrm{Cl}}^{139}$. The threshold was found to be 14.2 Mev. The ${\mathrm{Cl}}^{39}$ activity was found to have two beta-particles of energies 2.96 and 1.65 Mev, and two gamma-rays of energies 1.31 and 0.35 Mev, the low energy gamma-ray having a conversion coefficient of 0.05. A decay scheme is proposed. Consideration of the results show that ${\mathrm{A}}^{39}$ must have a half-life greater than five years or a decay energy of less than 0.4 Mev.

• Received 19 June 1950

DOI:https://doi.org/10.1103/PhysRev.80.318