Thick-target yields for the three important nuclear processes giving rise to the long-lived radioactive sulfur isotope are reported. The cross sections calculated from yield values favor the assignment of the activity to ${\mathrm{S}}^{35}$. The upper limit for the negative electrons emitted by active sulfur is found by absorption measurements in A1 and Cellophane to be 120±15 kev. The half-life is 88±3 days. It is concluded that neutron irradiation of carbon tetrachloride affords the most efficient means whereby samples of radioactive sulfur adequate for tracer work may be obtained. The chemical extraction of the sulfur is described and the application of the procedure to large scale production found feasible. Some preliminary investigations on the chemistry of the recoil sulfur produced in the nuclear reactions studied are reported. It is observed that resonance neutrons (absorbed by Cd) are effective in producing sulfur by the ($n,p$) process analogous to the ${\mathrm{N}}^{14}\mathrm{}(n,p)\mathrm{}{\mathrm{C}}^{14}$ reaction.

• Received 3 September 1941

DOI:https://doi.org/10.1103/PhysRev.60.537