Proton drip-line.

IDENTIFICATION OF THE PROTON DRIP LINE

( in collaboration with YASNAPP-group of JINR - Dubna, Russia )

see for details "Identification of the proton drip line", Z.Phys. A311, 245 (1983)

In order to determine the nuclear stability line against the radioactive decay with emission of the monochromatic 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.

Nuclei with 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.

This work can be done in two steps:

First, one must have full and reliable data on alpha decay energies in these chains.
Second, one must find masses of nuclei at the bottom of these alpha chains.

The first stage of this work ( to remove breaks in alpha chains ) has been perfomed in our work

Preprint ( in Russian ) of Leningrad Nuclear Physics Institute,

"The study of short-lived alpha emitters of 157Lu, 153Tm on

"New Neutron-deficient Lutetium Isotopes",

"New isotope 159Lu and decay of 158Lu,159,158Yb isotopes",

and in

E. Hagberg et al. Nucl. Phys. A293, 1 (1977)
S. Hoffmann et al. Z.Phys. A291, 53 (1979)
U.J.Schrewe et al. AECL-7408, 27, (1981)

The second stage has been done at IRIS facility

"Study of short-lived nuclei in the region Z=59-68",
Z.Phys., A310, 247 (1983).

using the 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:

148 Dy, 149 Dy, 149 Ho, 150 Ho, 151 Ho, and 152 Ho

Using these data and energies of alpha particles, we have calculated masses of nuclides bound in alpha chains and as the result the values of the last proton binding energies ( Bp ) for a number of nuclides ( see Fig. )

It follows from the figure that the nuclides

175 Au, 169 Ir, 171 Ir, 165 Re and probably 161 Ta

are unstable against the direct proton emission.

Using the obtained systematics for the neighbour nuclei it is possible to make the conclusion that nuclides

176 Au, 177 Au, 170 Ir and 166 Re

are also the proton emitters, and

178 Au, 172 Ir, 167 re, 156 Lu

could be considered as possible candidates for this type of decay.

For nuclides with even Z numbers the pairing effect shifts the drip line toward the larger excess of protons.

The obtained information allows us to locate the proton drip line. In this region of nuclei it runs ( for odd Z nuclides ) through

178 Au, 172 Ir, 167 Re, 161 Ta, 156 Lu and 151 Tm

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