Delayed radioactivity from the nuclei 17N and 90Nb

A hybrid analog--digital system was developed for use in collection of radioactivity data from nuclei with lifetimes greater than 1 millisecond. This system was used to study isomeric levels in the millisecond region in 90Nb. The half life of the 1+ excited state at 382 keV was measured to be 6.3 +- 0.2 milliseconds. Evidence is presented for another isomer within 10 keV of the 1+ level with a half life of 84.7 +- 6.2 milliseconds. 3He filled proportional counters were used for delayed neutron spectroscopy of 17N. Branching ratios for 17N to neutron unbound states in 17O were measured. The measured branching ratios as a function of excitation energy in 17O are 27 +- 3% to the 4.55 MeV state, 57 +- 6% to the 5.08 MeV state, and 11 +- 2% to the 5.94 MeV state. An upper limit of 0.4% was determined for branches to levels between 6.1 and 6.9 MeV in 17O. Three other delayed neutron emitters were produced using heavy ion reactions. Absolute cross sections measured for 3H(7Li,p)9Li, 7Li(7Li,p)13B and 11B(7Li,p)17N are 3.23 +- 1.1 mb at 30 MeV, 0.66 +- 0.2 mb at 26 MeV, and 1.3 +- 0.2 mb at 35 MeV. Delayed neutron measurements are complicated by interference from free neutrons contained in the target room. These free neutrons were found to leave the target room exponentially in time, with a mean life of 2.89 +- 0.9 milliseconds