L. T. Brown

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}

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.}

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.}

{alpha}-decay properties of {sup 190}Po and the identification of {sup 191}Po

The {alpha}-decay properties of {sup 190}Po were investigated through the use of a fragment mass analyzer in conjunction with a double-sided Si strip detector. The isotope was produced via the {sup 96}Mo({sup 96}Mo,2n) reaction, and its {alpha}-decay energy and T{sub 1/2} were measured as 7529(10) keV and 2.4{sub {minus}0.3}{sup +0.4} ms, respectively. The resulting reduced width is nearly identical to that of the {sup 192,194}Po isotopes. This is believed to result from significant mixing between the ground state {pi}(2p) and the low-lying 0{sup +}{pi}(4p-2h) intruder state in the Po parent. The result provides further evidence for shape coexistence in the light Po isotopes. In addition, {sup 191}Po was unambiguously identified, and the {sup 186}Pb {alpha}-decay branch was determined experimentally for the first time. {copyright} {ital 1997} {ital The American Physical Society}

α-decay properties of190Po and the identification of191Po

The {alpha}-decay properties of {sup 190}Po were investigated through the use of a fragment mass analyzer in conjunction with a double-sided Si strip detector. The isotope was produced via the {sup 96}Mo({sup 96}Mo,2n) reaction, and its {alpha}-decay energy and T{sub 1/2} were measured as 7529(10) keV and 2.4{sub {minus}0.3}{sup +0.4} ms, respectively. The resulting reduced width is nearly identical to that of the {sup 192,194}Po isotopes. This is believed to result from significant mixing between the ground state {pi}(2p) and the low-lying 0{sup +}{pi}(4p-2h) intruder state in the Po parent. The result provides further evidence for shape coexistence in the light Po isotopes. In addition, {sup 191}Po was unambiguously identified, and the {sup 186}Pb {alpha}-decay branch was determined experimentally for the first time. {copyright} {ital 1997} {ital The American Physical Society}

Spectroscopy of {sup 193,195,197}Po

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}

Fine structure in the {alpha} 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.}

Behavior of intruder based states in light Bi and Tl isotopes: the study of 187Bi α decay

Intruder state excitation energies in odd-mass nuclei just outside a closed proton shell plotted versus neutron number generally exhibit parabola-shaped curves with minima near neutron mid-shells. The Bi isotopes, however, do not seem to follow this trend. Recent experiments performed at Argonne National Laboratory have identified the previously unobserved {sup 187}Bi ground state (h{sub 9/2}) to {sup 183}TI ground state s{sub 1/2} {alpha} transition. Its energy when combined with those of two earlier known transitions, namely {sup 187}Bi (h{sub 9/2}) {yields} {sup 183m}Tl (h{sub 9/2}) and {sup 187m}Bi (s{sub 1/2}) {yields} {sup 183}Tl(s{sub 1/2}), establishes the excitation energies of the {sup 183m}Tl and {sup 187m}Bi to be 620(20) keV and 110(20) keV, respectively. This value for {sup 187m}Bi is 80 keV lower than the excitation energy of the same intruder level in {sup 189}Bi. Implications of this result with respect to intruder-state systematics are discussed.

Spectroscopy of {sup 192}Po

Author(s): Younes, W; Cizewski, JA; Jin, H; Bernstein, LA; McNabb, DP; Davids, CN; Janssens, RV; Khoo, TL; Lister, CJ; Blumenthal, DJ; Carpenter, MP; Henderson, D; Henry, RG; Lauritsen, T; Nisius, DT; Penttila, HT; Drigert, MW | Abstract: Prompt, in-beam γ rays following the reaction Yb170 + 142 MeV Si28 were measured at the ATLAS facility using 10 Compton-suppressed Ge detectors and the Fragment Mass Analyzer. Transitions in Po194 were identified and placed using γ-ray singles and coincidence data gated on the mass of the evaporation residues. A level spectrum up to J10 was established. The structure of Po194 is more collective than that observed in the heavier polonium isotopes and indicates that the structure has started to evolve toward the more collective nature expected for deformed nuclei.