Artificial Radioactive Isotopes of Thallium, Lead, and Bismuth

The radioelements produced by deuteron and neutron bombardment of thallium and lead have been investigated. The cloud chamber was used to observe the sign of the particles and the energies were determined from absorption measurements. A low intensity 65-min. lead isotope is formed by the deuteron bombardment of Tl; it emits gamma-rays and electrons of 1.00-Mev energy. The properties of two radioelements reported in a preliminary note have been more thoroughly studied. The long-lived thallium isotope produced by deuteron and neutron bombardment of Tl has a half-life of 3.5±0.5 years; it emits negative beta-particles with a maximum energy of 0.87 Mev. The provisional assignment is to ${\mathrm{Tl}}^{206}$. The 52-hour Pb isotope from the deuteron bombardment of Tl emits gamma-rays (450 kev), conversion electrons (370 kev), and x-rays (95 kev). Its assignment is uncertain. Two activities first obtained by others from the deuteron bombardment of Pb have been studied. The half-life of the 3-hour Pb was measured as 3.32±0.03 hours and its beta-ray energy as 0.70 Mev. The 6.4-day Bi was found to emit gamma-rays of 1.1 Mev and electrons of 0.86 Mev. The excitation functions for these two activities were measured; that for the 6.4-day Bi indicates that a $d-n$ reaction is responsible for its production. The recently reported 10-min. positron activity in Pb and 18-hour Bi activity could not be confirmed.