Radioactivity Produced by Proton Bombardment of Bromine and Iodine

Bromine bombarded with 5-6-Mev protons emits electrons with half-lives 13±2 seconds and 55±2 seconds. A $\beta$-spectrograph shows these to be conversion electrons from at least two gamma-rays of energies 127 and 187 kev. Physical and chemical tests indicate the activity is from a krypton isotope. The long period ${\mathrm{Kr}}^{79,81}$ reported by Snell is found to have a half-life of 34.5±1 hours and a positron upper limit of about 0.4 Mev. Iodine targets similarly emit electrons with a half-life of 75±1 seconds, shown to be conversion electrons from at least two gamma-rays of energies 125 and 175 kev, coming from a xenon isotope. Radiation consisting of electrons, x-rays, and probably gamma-rays, decaying with a half-life of 34±2 days is also found. Secondary electrons produced in the target material or in Pb absorbers by x-rays from the source account for about $\frac{2}{3}$ of the total activity measured by the electroscope.