J. Wauters

Alpha decay of [sup 186]Pb and [sup 184]Hg: The influence of mixing of 0[sup +] states on [alpha]-decay transition probabilities

Fine structure in the [alpha] decay of mass-separated [sup 186]Pb and [sup 184]Hg has been studied at the GSI on-line mass separator. Alpha singles spectra as well as [alpha]-x-[ital t] and [alpha]-[ital e]-[ital t] coincidence events were collected. The [alpha] decay of [sup 186]Pb revealed feeding to a low-lying 0[sup +] state at 328(12) keV in [sup 182]Hg. This state can be interpreted as being the bandhead of the deformed rotational band observed previously in in-beam studies. In the [alpha] decay of [sup 184]Hg, feeding towards the first excited 2[sup +] state at 153 keV and the 0[sub 2][sup +] state at 478 keV in [sup 180]Pt was observed. The hindrance factor of the [alpha] decay towards the excited 0[sup +] state gives information about the particle-hole character of the states connected in the [alpha] decay. A two-level mixing calculation is introduced. From the mixing in Pt and the [alpha]-decay hindrance factors, small mixing is deduced fro ground stattes of neutron-deficient Hg and Pb nuclei.

-decay characteristics of neutron-deficient 190, 192Po nuclei and alpha branching ratios of 186, 188Pb isotopes

By using complete fusion reactions and , leading to and compound nuclei, improved -decay characteristics for neutron-deficient isotopes have been obtained. The experiments have been performed at the fragment mass analyzer (Argonne) and at the RITU gas-filled separator (Jyvaskyla). In the l = 0 decay to the excited state in is two times faster than the decay to the ground state. For more precise values of the alpha-decay energy keV and half-life ms were measured. By using correlated -decay chains -branching ratios of 38(9)% and 9.3(8)% were experimentally deduced for the first time for and , respectively. The reduced -width systematics is extended for even Po isotopes, confirming a persistence of the saturation towards the lighter isotopes. Absence of any anomalies in the reduced -widths for the neutron-deficient Pb isotopes is confirmed.

Spectroscopy of193,195,197Po

Excited states built on the 13/2{sup +} isomers of the odd-mass {sup 193,195,197}Po isotopes have been observed via in-beam {gamma}-ray spectroscopy. The {alpha} radioactivity of these isotopes has been used to tag {gamma}-ray transitions following the {sup A}Er+164 MeV {sup 32}S reactions, where A=164, 166, 167, 168, and 170. Prompt {gamma} radiation was measured by ten Compton-suppressed Ge detectors at the target position and the Fragment Mass Analyzer was used to select evaporation residues. The results are compared with the first excited states of the heavier odd-mass polonium isotopes and of the even-mass cores. {copyright} {ital 1997} {ital The American Physical Society}

OCTUPOLE DEFORMATION IN AC-223

Abstract The level structure of 223Ac has been obtained from a study of the α-decay of mass separated 227Pa. Two levels connected by a fast E1 transition and with spin and parity 5+ 2 and 5− 2 were found: they form a parity doublet suggestive of octupole deformation in this nucleus. The Coriolis matrix element obtained for the mixing between the low-lying states is found to be attenuated, in agreement with theoretical expectations for stable octupole deformation.

Fine structure in the α decay of 192Po

Fine structure in the {alpha} decay of {sup 192}Po has been studied in the reaction of {sup 36}Ar on {sup 160}Dy at 176 MeV. Evaporation residues were selected in-flight using the Argonne Mass Analyzer and implanted into a double sided silicon strip detector. The correlation technique between implants and subsequent decays was used to observe fine structure in the {alpha} decay of {sup 192}Po leading to the identification of an excited 0{sup +} state in {sup 188}Pb at 571(31) keV. The half-life of {sup 192}Po has been determined to be 33.2(14) ms. The observation of a low-lying 0{sup +} state is discussed in terms of proton particle-hole pair excitations across the Z=82 shell gap. The small hindrance factor to the excited 0{sup +} state relative to the ground state supports the picture of shape coexistence in light even-even Po isotopes. {copyright} {ital 1997 American Institute of Physics.}

Single-particle and cluster levels in {sup 107,108,109}Sn populated in the decay of {sup 107,108,109}Sb

New features of the level structures of 107,108,109Sn that have been observed following the beta decay of 107,108,109Sb are reported. The recoiling Sb nuclides were isolated using the Fragment Mass Analyzer at the ATLAS accelerator facility. Low-energy levels with strong configuration admixtures of the (νg7/2)5/23 are identified in both 107Sn and 109Sn.

Gamow-Teller strength in the

At the LISOL facility the neutron-deficient {sup 54}Ni isotope was produced via a {sup 3}He fusion-evaporation reaction on a {sup 54}Fe target positioned in the element-selective Ion-Guide Laser Ion Source (IGLIS). The {beta} decay of {sup 54}Ni was observed for the first time. The Gamow-Teller {beta}-decay strength associated with the (J{sup {pi}}=1{sup +}) level at 937.2 keV in the daughter nucleus {sup 54}Co was deduced. The Gamow-Teller {beta}-decay strength is in agreement with B(GT) obtained from (p,n) reaction studies. For the first time an experiment was performed using a heavy-ion beam in combination with the IGLIS in order to produce {sup 42}Ti.

Gamow-Teller strength in the f{sub 7/2}-nuclei {sup 54}Co and {sup 42}Sc studied through the beta decay of {sup 54}Ni and {sup 42}Ti

At the LISOL facility the neutron-deficient {sup 54}Ni isotope was produced via a {sup 3}He fusion-evaporation reaction on a {sup 54}Fe target positioned in the element-selective Ion-Guide Laser Ion Source (IGLIS). The {beta} decay of {sup 54}Ni was observed for the first time. The Gamow-Teller {beta}-decay strength associated with the (J{sup {pi}}=1{sup +}) level at 937.2 keV in the daughter nucleus {sup 54}Co was deduced. The Gamow-Teller {beta}-decay strength is in agreement with B(GT) obtained from (p,n) reaction studies. For the first time an experiment was performed using a heavy-ion beam in combination with the IGLIS in order to produce {sup 42}Ti.

Evolution of collective motion in light polonium nuclei.

The {gamma}-ray spectroscopy of even- and odd-mass isotopes of polonium have been studied using arrays of Ge detectors coupled to recoil-mass analyzers, including recoil-decay tagging techniques. The level energies and B(E2) branching ratios can be reproduced by theoretical frameworks which do not explicitly include proton particle-hole excitations across the Z = 82 shell, conclusions in contrast to those deduced from alpha-decay measurements.

Fine structure in the α decay of [sup 192]Po

Fine structure in the {alpha} decay of {sup 192}Po has been studied in the reaction of {sup 36}Ar on {sup 160}Dy at 176 MeV. Evaporation residues were selected in-flight using the Argonne Mass Analyzer and implanted into a double sided silicon strip detector. The correlation technique between implants and subsequent decays was used to observe fine structure in the {alpha} decay of {sup 192}Po leading to the identification of an excited 0{sup +} state in {sup 188}Pb at 571(31) keV. The half-life of {sup 192}Po has been determined to be 33.2(14) ms. The observation of a low-lying 0{sup +} state is discussed in terms of proton particle-hole pair excitations across the Z=82 shell gap. The small hindrance factor to the excited 0{sup +} state relative to the ground state supports the picture of shape coexistence in light even-even Po isotopes. {copyright} {ital 1997 American Institute of Physics.}