Beta-delayed proton emission: a new series of precursors, and the measurement of 10-16 s nuclear lifetimes

The results of investigation into a new series of Z-even nuclei - precursors of delayed protons (PDP) -65Ge, 89Se, 93Kr, 81Zr, and 85Mo are presented. PDP were obtained by irradiation of targets in the following reactions: Zn(He, 2n) 65Ge, 22 MeV; 40Ca(32S, 2 pn) 19Se, 100 MeV; 60Ni (160, 3 n), 73Kr, 75 MeV; 52Cr (32S, 3n)81Zr, 110 MeV; 56Fe(32S, 3n)85Mo, 120 MeV. The targets (self-sustaining foils of thickness approximately 1.2 mg/cm2) were placed at an angle of 15 deg to the direction of the ion beam. Upon irradiation targets were moved downwards into a measuring position. The spectra of protons, X and gamma-rays, and also the spectra of p - x, p-γ, x - γ coincidences accompanying the decay of 65Ge, 69Se,73Kr and 81Zr, and 85Mo were measured. The measured half-lives are equal, to 31.5+-1.9, 27.3+-0.5, 28.5+-1.1, 6.3+-0.5, and 5.6 +-0.9 s respectively. The experimental spectra are compared with the calculated ones. The proton spectrum is determined by two factors: (1) the intensity of the branches of the β-decay (including electron capture) from a precursor to a radiator, and (2) the branching ratio in the states of a daughter nucleus with subsequent proton emission. If the lifetime of a proton-emitting state is shorter than that of the K-vacancy (3.5 x 10-16 s), then the X-rays coinciding with the protons characterize the (Z-2) daughter nucleus. Otherwise they characterize the (Z-1) radiator