The proton pairing energies ( odd-even mass differences ) were obtained using the measured mass values and data from literature for very wide region of nuclei far from stability. It was shown that the proton pairing energies tend to increase as the proton excess grows in a wide range of mass numbers. These values for the proton emitters are about 50 % as large as those for nuclides near the beta stability line.
Preliminary rough estimates of the neutron pairing energies for very neutron-deficient nuclei of this region allow us to establish the same trend. A similar behaviour of the proton and neutron pairing energies seems somewhat amazing and could be caused by the proximity of the proton drip-line and the influence of the Coulomb barrier on the pairing processes.
In order to determine the nuclear stability line against the radioactive decay with emission of a monoenergetic proton, it is necessary to reveal cases when the binding energy of the proton becomes negative. Direct measurements of nuclide masses near this line are very difficult ( if possible ) at present. This work was done in two steps using nuclear spectroscopy methods on-line : First, one had to get full and reliable data on alpha decay energies in these chains. Second, one had to find masses of nuclei at the bottom of these alpha chains. Nuclei with a large neutron deficiency in the region A > 150 are mostly alpha emitters. It gives a possibility to obtain the data on masses of these nuclei near the proton drip line using energies of alphas in long alpha decay chains. Alpha decay energies for long decay chains were studied carefully using Si(Au)-solid state detectors to deduce masses of nuclei far off the beta stability line. The first stage of this work ( to fill the breaks in alpha chains ) has been performed in our work and other data were taken from the literature. The second stage has been done at IRIS facility using an intrinsic germanium detector Ge(HP) to study positron spectra of nuclei in the ends of alpha chains. The obtained values of endpoint energies of positron spectra and derived isobar mass differences allowed us to determine masses of nuclides at the bottom of chains:Using these data and energies of alpha particles, we have calculated masses of nuclides bound in alpha chains and as the result obtained the values of the last proton binding energies ( B p ) for a number of nuclides.
The heavy nuclides with Z > 86 are a subject of great interest in nuclear astrophysics because they are produced during the r-process ( rapid neutron capture under astrophysical conditions ). The very long-lived nuclides of 232Th, 238U, 244Pu, etc. are produced by beta-transitions occurring after r-process “freezing”. These nuclides, due to their long half-lives can be used as nuclear cosmochronometers. The estimated values of the age of the Universe are strongly dependent on the beta-delayed fission rates of the neutron-rich nuclei with mass numbers A > 232 far off the stability line. A very low limit was set in our experiments for delayed fission rates of nuclei of cosmochronological interest. The results give new clues regarding the problem of the location of the r-process path in the heavy mass region. The results also show it is quite possible to consider the beta-decay chain with A=232 from the r-process path to the cosmochronometer 232Th without any delayed fission. It may lead us to a reconsideration of the production rate of 232Th during the nucleosynthesis in the Galaxy.