On-Line Alpha Spectroscopy of Neutron-Deficient Radium Isotopes

Isotopes of radium lighter than mass 215 were studied by bombardment of

{}^{206}{Pb}

with

{}^{12}C

and

{}^{197}{Au}

with

{}^{19}F

. Si(Au) surface-barrier detectors were used in on-line measurements to measure

α

-decay characteristics. Mass-number assignments of

{}^{214}{Ra}

through

{}^{206}{Ra}

were made on the basis of excitation functions and genetic relationships with francium, emanation, and astatine isotopes. Half-lives and accurate

α

energies were determined for the radium isotopes, and the

α

energy of

{}^{214}{Fr}

was corrected.

α

and

β

branchings were measured for

{}^{213}{Ra}

and

{}^{214}{Ra}

. Some systematic trends in the

α

-decay energies were interpreted in terms of weakening neutron and proton pairing energies near closed shells.

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