Delayed-neutron emission probabilities ($P_n$) were measured for 16 isotopes of Br, Rb, I, and Cs. Sources of chemically and mass separated nuclides were obtained from an on-line mass spectrometer facility. Neutrons were counted in a multitube polyethylene-moderated detector. The total number of precursor atoms was determined by direct counting of ions deposited on the first dynode of an electron multiplier. The $P_n$ values from this work generally agree with earlier measurements for the longer-lived precursors but are consistently higher for the shorter-lived precursors. A log-log plot of $P_n$ versus the reduced energy window $\frac{(Q_{\beta }-B_n)}{(Q_{\beta }-C)}$ gives a straight line with a slope of 6.0 ± 1.4 in agreement with simplified theoretical predictions. Half-lives of Rb and Cs nuclides measured by neutron decay curves are given.

RADIOACTIVITY ${}_{}{}^{87,88,89}{}_{}{}^{}\mathrm{Br}$, ${}_{}{}^{92,93,94,95,96,97}{}_{}{}^{}\mathrm{Rb}$ ${}_{}{}^{137,138}{}_{}{}^{}\mathrm{I}$, ${}_{}{}^{141,142,143,144,145}{}_{}{}^{}\mathrm{Cs}$; measured $P_n$, $T_{\frac{1}{2}}$; on-line mass separation, polyethylene-moderated neutron counter.

• Received 20 September 1976

DOI:https://doi.org/10.1103/PhysRevC.15.2108