K. S. Vierinen

Alpha-decaying low-spin levels in155Lu and157Lu

Using an on-line mass separator, the α-particle decays of155Lu and157Lu were investigated. A new α-emitting level in157Lu was identified [T1/2=5.7(5) s,Eβ=4924(20) keV]. In addition, a half-life of 140(20) ms was measured for the recently discovered second, low-lying, α-decaying level [Eβ=5579 (5)keV] in155Lu.

Spectroscopy of proton-rich nuclei in the rare earth region

Abstract The isotope separator facility OASIS, on-line at the Lawrence Berkeley Laboratory Super-HILAC, was used to investigate proton-rich rare earth nuclei. Single-particle states near the 82-neutron shell were delineated, numerous new isotopes, isomers and β-delayed proton emitters were discovered and the α-decay properties of some nuclides with N ⩾ 84 were re-examined. In this contribution the experimental program is summarized briefly, the excitation energies of the s 1 2 and h 11 2 proton states in this mass region are discussed, and results on the β-delayed-proton spectra of 145Dy and 147Er are presented.

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.

Nuclear spectroscopy in the rare earth region near the proton drip line

We have used the isotope separator facility OASIS, on-line at the Lawrence Berkeley Laboratory SuperHILAC, to investigate rare-earth nuclei close to the proton drip line. Single-particle states near the 82-neutron shell have been examined and their excitation energies determined. Numerous new isotopes, isomers, and β,-delayed proton emitters have been discovered. In addition, the a -decay properties of nuclides with N ≥ 84 have been reexamined; this has led to the discovery of several previously unobserved a transitions. The overall experimental program is summarized and some recently obtained results on 145Dy, 147Er, 147Tm, 153Lu155Lu, and 157Lu are discussed.

Identification of153Lu β decay

Using an on-line mass separator the decay of153Lu was studied in64Zn bombardments of92Mo. The T1/2=0.9 ±0.2 s activity was assigned to the β decay of the (11/2−) isomer.

Identification of the neutron-rich isotope174Er

The heaviest known erbium isotope, 3.3(2) min.174Er, has been identified using on- line isotope separation and by ß and γ- ray spectroscopy. Twelve γ rays were placed in a preliminary decay scheme. The mass of the new isotope was established by the separator and the Z was deduced from Tm K x ray coincident ß and γ rays. In addition, the heaviest known isotope of holmium171Ho was observed with a half-life of 49(5) s.

Beta decay ofLu154andYb154

Using mass-separated sources, the ..beta..-decay properties of /sup 154/Lu and /sup 154/Yb were investigated. Limits of /sup 154/Lu decay to the first 8/sup +/ and 6/sup +/ levels in /sup 154/Yb suggest a 7/sup +/ spin for the odd-odd parent; also delayed proton emission and an indication of delayed ..cap alpha..-particle emission were observed to follow /sup 154/Lu ..beta.. decay. The ..beta..-decay branch of the ..cap alpha..-emitting nucleus /sup 154/Yb was identified for the first time by the observation of one intense 133.2-keV ..gamma.. ray. This transition deexcites a 1/sup +/ 133.2-keV level in /sup 154/Tm which is fed by an allowed 0/sup +/..-->..1/sup +/..beta.. transition with a logft value of 3.6 +- 0.3.

Beta decay of Lu154 and Yb154

Using mass-separated sources, the ..beta..-decay properties of /sup 154/Lu and /sup 154/Yb were investigated. Limits of /sup 154/Lu decay to the first 8/sup +/ and 6/sup +/ levels in /sup 154/Yb suggest a 7/sup +/ spin for the odd-odd parent; also delayed proton emission and an indication of delayed ..cap alpha..-particle emission were observed to follow /sup 154/Lu ..beta.. decay. The ..beta..-decay branch of the ..cap alpha..-emitting nucleus /sup 154/Yb was identified for the first time by the observation of one intense 133.2-keV ..gamma.. ray. This transition deexcites a 1/sup +/ 133.2-keV level in /sup 154/Tm which is fed by an allowed 0/sup +/..-->..1/sup +/..beta.. transition with a logft value of 3.6 +- 0.3.

BETA-DECAY OF [SUP]154 LU AND [SUP]154 YB

Using mass-separated sources, the ..beta..-decay properties of /sup 154/Lu and /sup 154/Yb were investigated. Limits of /sup 154/Lu decay to the first 8/sup +/ and 6/sup +/ levels in /sup 154/Yb suggest a 7/sup +/ spin for the odd-odd parent; also delayed proton emission and an indication of delayed ..cap alpha..-particle emission were observed to follow /sup 154/Lu ..beta.. decay. The ..beta..-decay branch of the ..cap alpha..-emitting nucleus /sup 154/Yb was identified for the first time by the observation of one intense 133.2-keV ..gamma.. ray. This transition deexcites a 1/sup +/ 133.2-keV level in /sup 154/Tm which is fed by an allowed 0/sup +/..-->..1/sup +/..beta.. transition with a logft value of 3.6 +- 0.3.