A radioactive isotope of 2.4-day half-life has been produced in bromine by deuteron bombardment of electromagnetically enriched ${\mathrm{Se}}^{76}$, and by alpha-particle bombardment of electromagnetically enriched ${\mathrm{Se}}^{74}$. Assignment of the isotope is made to ${\mathrm{Br}}^{77}$. A positron end point of 0.4 Mev is determined. In addition to annihilation radiation, gamma-rays and $K$-capture are observed. The ratio of $K$-capture to positron emission is determined to be 20. The cross-section ratio of the $d,n$ to the $d,2n$ reaction producing the isotope is 0.3. The ratio of the sum of the cross sections for formation of ${\mathrm{Br}}^{77}$ by ${\mathrm{Se}}^{76}\mathrm{}(d,n)\mathrm{}$ and ${\mathrm{Se}}^{77}\mathrm{}(d,2n)\mathrm{}$ to the cross section for ${\mathrm{Br}}^{82}$ by ${\mathrm{Se}}^{82}\mathrm{}(d,2n)\mathrm{}$ is 0.4. A radioactive isotope of 1.7-hour half-life has been produced in bromine by deuteron bombardment and by proton bombardment of enriched ${\mathrm{Se}}^{74}$. Assignment of the isotope is made to ${\mathrm{Br}}^{75}$. A positron end point of 1.6 Mev is determined. $K$-capture is observed in the activity. No gammaray activity other than that due to annihilation is found. The ratio of $K$-capture to positron emission from the ${\mathrm{Se}}^{74}\mathrm{}(d,n)\mathrm{}$ reaction is determined to be 4.4. The ratio of the cross section for formation of ${\mathrm{Br}}^{75}$ by ${\mathrm{Se}}^{74}\mathrm{}(d,n)\mathrm{}$ to that of ${\mathrm{Br}}^{82}$ by ${\mathrm{Se}}^{82}\mathrm{}(d,2n)\mathrm{}$ is 2.1. The 4.4-hour ${\mathrm{Br}}^{80}$ isotope has been produced by a $\mathrm{Se}(\alpha ,p)$ reaction and found to emit positrons with an end point of 0.8 Mev. In producing ${\mathrm{Br}}^{77}$ by proton bombardment of Se the $p,\gamma e$ reaction is observed to be two-thirds as probable as the $p,n$ reaction.

• Received 2 July 1948

DOI:https://doi.org/10.1103/PhysRev.74.870