A study of the radioactive isotopes of bromine has been carried out by cross checking a number of nuclear reactions induced by bombarding the elements arsenic, selenium, bromine, krypton and rubidium with neutrons, deuterons, and electrically accelerated $\alpha$-particles. The results indicate that the active isotope bromine 80 exists in two isomeric forms, from which it decays with the respective periods of 18 minutes and 4.5 hours. An example of two successive $\beta$-transitions is found to occur in the active isotopes selenium 83 and bromine 83, and a new type of transmutation is observed in which the emission of two neutrons apparently follows deuteron capture, the reaction in this case being ${\mathrm{Se}}^{82}\mathrm{}(D,2n)\mathrm{}{\mathrm{Br}}^{82}$. The discovery of a number of new radioactive isotopes and the identification of isotopes which carry some of the already-known activities have led to results which may be summarized in the following table of decay periods: All of these activities emit negative electrons except bromine 78 and possibly the krypton 18-hr. activity, which is very weak. Absorption measurements for the $\beta$-rays of the bromine isotopes have given the following values for their maximum energy: ${\mathrm{Br}}^{78}$ (6.4 min.) 2.3 Mev; ${\mathrm{Br}}^{80}$ (18 min.) 2.2 Mev; ${\mathrm{Br}}^{80}$ (4.5 hrs.) 2.0 Mev; ${\mathrm{Br}}^{82}$ (33.9 hrs.) 0.4 Mev; ${\mathrm{Br}}^{83}$ (2.45 hrs.) 1.3 Mev. The emission of $\gamma$-rays accompanies the activity of ${\mathrm{Br}}^{78}$, ${\mathrm{Br}}^{80}$ (18 min.) and ${\mathrm{Br}}^{82}$, but is not found with ${\mathrm{Br}}^{80}$ (4.5 hrs.) nor ${\mathrm{Br}}^{83}$.

• Received 3 August 1937

DOI:https://doi.org/10.1103/PhysRev.52.1007