D. C. Sousa

The α-decay rate of 188Pb

Abstract As part of our investigation of the reported anomalous α-decay rates of even-even lead nuclei with A ≦ 192 we have measured the α-decay branching ratio of 188 Pb. The isotope was produced in the 180 W( 16 O, 8n) reactions, and its decay properties were investigated with the use of the Oak Ridge on-line isotope separator facility. Gamma-ray and α-particle spectra were measured with the detectors placed in calibrated geometries. From these measurements the 188 Pb α-decay branching ratio was determined to be (22 ± 7)%, a value about seven times greater than that available in the literature. This result, together with our recent data for 190 Pb and 192 Pb, is discussed within the context of α-decay-rate systematics in the lead region.

Identification ofTb145andTb144and levels in theN=81nucleus,Gd145

With the use of a helium gas-jet transport system the isotopes /sup 145/Tb and /sup 144/Tb were identified in a series of /sup 10/B+/sup 144/Sm irradiations. Nuclidic assignments were based on yields as a function of bombarding energy, ..gamma..-ray coincidences with gadolinium K x rays and comparisons with data from in-beam ..gamma..-ray studies. Thirteen transitions were observed to follow the decay of /sup 145/Tb (T/sub 1/2/ = 30 +- 3 sec). None of them were placed in a scheme incorporating six excited levels in /sup 145/Gd, th lowest two of which, 27.3 and 748.7 keV, were previously known from decay /sup 145/Gd/sup m/ decay. The nuclide /sup 144/Tb (T/sub 1/2/ = 5 +- 1 sec) was identified by observing the 742.9-keV ..gamma.. ray known from in-beam studies to be the 2/sup +/ (first-excited state)..-->..0/sup +/ (ground state) transition in /sup 144/Gd.

Investigation of A =155 and A =151 nuclides: Identification of the sup 155 Tm s sub 1/2 isomer and of the sup 155 Yb. beta. -decay branch

The decay properties of {sup 155}Lu, {sup 155}Yb, {sup 155}Tm, and of the {alpha}-decay daughters {sup 151}Er and {sup 151}Ho were investigated following the on-line mass separation of {ital A}=155 nuclides produced in {sup 64}Zn irradiations of {sup 95}Mo. In the study, the half-life of the low-spin isomer in {sup 155}Lu was measured to be 140{plus minus}20 ms, the {beta}-decay branch of {sup 155}Yb was identified by observing daughter {gamma} rays and Tm {ital K} x rays, and the existence in {sup 155}Tm of an {ital s}{sub 1/2} isomer ({ital T}{sub 1/2}=44{plus minus}4 s), in addition to the {ital h}{sub 11/2} ground state ({ital T}{sub 1/2}=21.6{plus minus}0.2 s) was established. Schemes for the {beta} decays of {sup 155}Yb, {sup 155}Tm, and {sup 151}Er are proposed. New information on {sup 151}Er decay establishes the {ital s}{sub 1/2} isomer in {sup 151}Ho to be 41.1{plus minus}0.2 keV above the {ital h}{sub 11/2} ground state. Also, branchings of 90{plus minus}5, 28{plus minus}7, and 80{sub {minus}20}{sup +15}% were determined for the {alpha} decays of {sup 155}Yb, {sup 151}Ho, and {sup 151}Ho{sup {ital m}}, respectively.

Investigation ofA=155 andA=151 nuclides: Identification of theTm155s1/2isomer and of theYb155β-decay branch

The decay properties of {sup 155}Lu, {sup 155}Yb, {sup 155}Tm, and of the {alpha}-decay daughters {sup 151}Er and {sup 151}Ho were investigated following the on-line mass separation of {ital A}=155 nuclides produced in {sup 64}Zn irradiations of {sup 95}Mo. In the study, the half-life of the low-spin isomer in {sup 155}Lu was measured to be 140{plus minus}20 ms, the {beta}-decay branch of {sup 155}Yb was identified by observing daughter {gamma} rays and Tm {ital K} x rays, and the existence in {sup 155}Tm of an {ital s}{sub 1/2} isomer ({ital T}{sub 1/2}=44{plus minus}4 s), in addition to the {ital h}{sub 11/2} ground state ({ital T}{sub 1/2}=21.6{plus minus}0.2 s) was established. Schemes for the {beta} decays of {sup 155}Yb, {sup 155}Tm, and {sup 151}Er are proposed. New information on {sup 151}Er decay establishes the {ital s}{sub 1/2} isomer in {sup 151}Ho to be 41.1{plus minus}0.2 keV above the {ital h}{sub 11/2} ground state. Also, branchings of 90{plus minus}5, 28{plus minus}7, and 80{sub {minus}20}{sup +15}% were determined for the {alpha} decays of {sup 155}Yb, {sup 151}Ho, and {sup 151}Ho{sup {ital m}}, respectively.

Decay properties of /sup 150/Tm and /sup 150/Er

The decay properties of /sup 150/Tm and /sup 150/Er (produced in /sup 58/Ni bombardments of /sup 96/Ru) were investigated following on-line mass separation. The half-life of /sup 150/Tm was measured to be 2.2 +- 0.2 s rather than the value of 3.5 s available in the literature. Based on its decay characteristics, we suggest that this high-spin /sup 150/Tm isomer has a spin assignment of 6/sup -/. Among the /sup 150/Er states fed by this 6/sup -/ isomer is the yrast 4/sup +/ level (2294.8 keV) which up to now has been observed in neither ..beta..-decay nor in-beam ..gamma..-ray studies. New transitions observed in /sup 150/Er decay establish several previously unknown levels in /sup 150/Ho. While the additional ..gamma.. rays reduce from 100% to 96% the feeding to the 476-keV state in /sup 150/Ho known earlier, the corresponding logft value is calculated to be 3.6, indicating that this is an allowed, 0/sup +/..-->..1/sup +/, beta transition. Photon intensities obtained for ..gamma.. rays following the decay of the /sup 150/Ho low-spin isomer resolve inconsistent values measured in two previous investigations.

Decay properties ofTm150andEr150

The decay properties of /sup 150/Tm and /sup 150/Er (produced in /sup 58/Ni bombardments of /sup 96/Ru) were investigated following on-line mass separation. The half-life of /sup 150/Tm was measured to be 2.2 +- 0.2 s rather than the value of 3.5 s available in the literature. Based on its decay characteristics, we suggest that this high-spin /sup 150/Tm isomer has a spin assignment of 6/sup -/. Among the /sup 150/Er states fed by this 6/sup -/ isomer is the yrast 4/sup +/ level (2294.8 keV) which up to now has been observed in neither ..beta..-decay nor in-beam ..gamma..-ray studies. New transitions observed in /sup 150/Er decay establish several previously unknown levels in /sup 150/Ho. While the additional ..gamma.. rays reduce from 100% to 96% the feeding to the 476-keV state in /sup 150/Ho known earlier, the corresponding logft value is calculated to be 3.6, indicating that this is an allowed, 0/sup +/..-->..1/sup +/, beta transition. Photon intensities obtained for ..gamma.. rays following the decay of the /sup 150/Ho low-spin isomer resolve inconsistent values measured in two previous investigations.

Decay properties of Tm150 and Er150

The decay properties of /sup 150/Tm and /sup 150/Er (produced in /sup 58/Ni bombardments of /sup 96/Ru) were investigated following on-line mass separation. The half-life of /sup 150/Tm was measured to be 2.2 +- 0.2 s rather than the value of 3.5 s available in the literature. Based on its decay characteristics, we suggest that this high-spin /sup 150/Tm isomer has a spin assignment of 6/sup -/. Among the /sup 150/Er states fed by this 6/sup -/ isomer is the yrast 4/sup +/ level (2294.8 keV) which up to now has been observed in neither ..beta..-decay nor in-beam ..gamma..-ray studies. New transitions observed in /sup 150/Er decay establish several previously unknown levels in /sup 150/Ho. While the additional ..gamma.. rays reduce from 100% to 96% the feeding to the 476-keV state in /sup 150/Ho known earlier, the corresponding logft value is calculated to be 3.6, indicating that this is an allowed, 0/sup +/..-->..1/sup +/, beta transition. Photon intensities obtained for ..gamma.. rays following the decay of the /sup 150/Ho low-spin isomer resolve inconsistent values measured in two previous investigations.

Identification of Tb-145 and Tb-144 and levels in the N=81 nucleus, Gd-145

With the use of a helium gas-jet transport system the isotopes /sup 145/Tb and /sup 144/Tb were identified in a series of /sup 10/B+/sup 144/Sm irradiations. Nuclidic assignments were based on yields as a function of bombarding energy, ..gamma..-ray coincidences with gadolinium K x rays and comparisons with data from in-beam ..gamma..-ray studies. Thirteen transitions were observed to follow the decay of /sup 145/Tb (T/sub 1/2/ = 30 +- 3 sec). None of them were placed in a scheme incorporating six excited levels in /sup 145/Gd, th lowest two of which, 27.3 and 748.7 keV, were previously known from decay /sup 145/Gd/sup m/ decay. The nuclide /sup 144/Tb (T/sub 1/2/ = 5 +- 1 sec) was identified by observing the 742.9-keV ..gamma.. ray known from in-beam studies to be the 2/sup +/ (first-excited state)..-->..0/sup +/ (ground state) transition in /sup 144/Gd.

Identification of /sup 145/Tb and /sup 144/Tb and levels in the N = 81 nucleus, /sup 145/Gd

With the use of a helium gas-jet transport system the isotopes /sup 145/Tb and /sup 144/Tb were identified in a series of /sup 10/B+/sup 144/Sm irradiations. Nuclidic assignments were based on yields as a function of bombarding energy, ..gamma..-ray coincidences with gadolinium K x rays and comparisons with data from in-beam ..gamma..-ray studies. Thirteen transitions were observed to follow the decay of /sup 145/Tb (T/sub 1/2/ = 30 +- 3 sec). None of them were placed in a scheme incorporating six excited levels in /sup 145/Gd, th lowest two of which, 27.3 and 748.7 keV, were previously known from decay /sup 145/Gd/sup m/ decay. The nuclide /sup 144/Tb (T/sub 1/2/ = 5 +- 1 sec) was identified by observing the 742.9-keV ..gamma.. ray known from in-beam studies to be the 2/sup +/ (first-excited state)..-->..0/sup +/ (ground state) transition in /sup 144/Gd.