Beta-delayed two-neutron decay studies for 96-99Rb

Beta-delayed two-neutron emission from /sup 96-99/Tb has been studied by use of the neutron-neutron time correlation technique. Time interval distributions for neutron pulses from a polyethylene moderated neutron counter are measured for mass-separated sources. Coincident neutrons are identified in the time interval distribution by a component having the characteristic residence time of 35 mu s for this counter. At mass 98 a coincidence rate well above the correlated background results in a P/sub 2n/ for /sup 98/Rb of (0.060+or-0.009)%. Upper limits (2 sigma ) for P/sub 2n/ of 0.004, 0.008, and 0.024% are reported for /sup 96/Rb, /sup 97/Rb, and /sup 99/Rb, respectively. (10 refs).