Delayed Neutrons from 15.5-secBr88

A description is given of a gas-flow system which permits quick chemical isolation of bromine fission fragments. By use of this system, ${\mathrm{Br}}^{88}$ was found to be a delayed-neutron precursor resulting from the fission of ${\mathrm{U}}^{235}$. The half-life measured by neutron counting is 15.5±0.4 sec, in agreement with that previously measured for ${\mathrm{Br}}^{88}$ by radiochemical techniques. It is a relatively abundant source of delayed neutrons, producing per fission 3.5±1.5 times the number of neutrons in the 54-sec group having ${\mathrm{Br}}^{87}$ as a precursor. ${\mathrm{Br}}^{88}$ is the first definitely established case of a delayed-neutron precursor of odd proton and odd neutron number. Qualitative arguments are given to show that such nuclei are about as likely to be delayed-neutron precursors as are those of odd $Z$ and even $N$, although only the latter have been reported previously.