M. O. Kortelahti

Transition quadrupole moments of high-spin states in 170W

Abstract Lifetimes of states in 172Os have been measured by the Doppler-shift recoil-distance method. These states were populated by the reaction 144Nd(32S, 4n) 172Os at a bombarding energy of 162 MeV from the HHIRF tandem accelerator at ORNL. The data were collected in the γγ-coincidence mode in order to reduce the complexities of the γ-ray spectra and to avoid some of the problems associated with side feeding to excited states. The experimental transition quadrupole moments, Qt, do not cluster about a constant value as a function of rotational frequency up through h ω = 0.27 MeV as predicted by cranked Hartree-Fock-Bogoliubov (HFB) calculations around N = 96 for the yrast band. A striking feature in the experimental data for the yrast band is an abrupt increase of the Qt values for the 6+ and 8+ states where the first anomaly in the behavior of the moment of inertia occurs. A recent proposal of band-mixing between the yrast band and a quasi-β band to account for this anomaly in the moment of inertia also seems to provide a logical interpretation of the Qt values at low rotational frequencies. The large collectivity inferred for the quasi-β band from our Qt values for the 6+ and 8+ states is an indirect, but plausible, argument that the quasi-β band corresponds to the non-yrast band in the band-mixing model. The E1 transition probabilities for decay of states in the (π, α) = (−, 1) band to states in the ground-state band range between 1.4 × 10−5 to 3.1 × 10−4 W.u. The B(E1, I → I + 1) is an order of magnitude larger than the B(E1, I → I − 1). The origin of these effects can probably be understood in terms of a predominant admixture of the Coriolis-coupled octupole vibrational-state wave function in the (−, 1) band of 172Os at low spin.

Decay of mass-separated 189mHg (8.7 min) and 189gHg (7.7 min) to 189Au

Abstract The decays of 189Hg (8.7 min; J π = 13 2 + ) and 189Hg (7.7 min; J π = 3 2 − ) have been studied with mass-separated sources from the UNISOR facility. Multiscaled spectra of γ-rays, X-rays, and conversion electrons, as well as γγt, γXt, eγt, and eXt coincidences were obtained. Decay schemes have been constructed incorporating > 95% of the decay intensities assigned to the high-spin and low-spin decays. The γ-ray gated conversion-electron spectra permitted the determination of 119 conversion-electron subshell ratios. Portions of the level scheme bear a remarkable resemblance to the heavier and lighter odd-mass Au isotopes. An extensive band of states is observed built upon the h 9 2 intruder state at 325 keV. This band is markedly different from the corresponding bands in 187Au and 185Au, indicating a major change in the cores, i.e. between 188Pt and 186,184Pt. Evidence for oblate-hole-prolate-particle symmetry in 189Au is discussed. Completeness of complex decay schemes far from stability is addressed.

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.

Very converted transitions and particle-core coupling in neutron-deficient odd-mass au isotopes

Levels in185, 187Au have been studied by radioactive decay of isotopically separated185, 187Hg. A number of low-energy very-converted transitions are observed in the decay. It is shown that the enhanced conversion in these cases comes from an E0 component rather than from an anomaly in theM1 conversion process. A systematic pattern of bands interconnected with these very converted transitions is presented as evidence for a new type of particle-core coupling in185, 187Au.

Investigation of A=155 and A=151 nuclides: Identification of the Tm155 s1/2 isomer and of the Yb155 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 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.

Non-yrast level structure of35Nd via beta decay of135Pm

The isotope135Nd has been studied through the β-decay of mass-separated135pm. He-jet transported samples without mass-separation were also studied. The parent135Pm has isomers with β-decay half-lives of 40±3 s and 49±3 s. The low-lying non-yrast structure of135Nd is shown to consist of a group of levels which decay to a 65.1-keV isomeric level which is not reached in the yrast cascades.

Beta-delayed proton decay of theN=83 precursor153Yb

Beta-delayed proton emission was observed for the N=83 precursor153Yb. This extends the region of delayed proton emission in the lanthanides across the N=82 shell for the first time. The 4.0±0.5 s delayed proton activity was assigned to153Yb on the basis of mass separation, coincident Tm K x rays, and coincident γ-ray transitions in the daughter nucleus152Er. Proton final state branching ratios are consistent with a 7/2- precursor spin. The proton branching ratio is (8±2)×l0−5.

Energy levels of136Pm and136Nd via beta decay of136Sm and136Pm

Abstract136Pm and136Nd were studied using theβ decay of136Sm and136Pm. The radioactive nuclei were produced by the92Mo (48Ti,xpyn) and112Sn (28Si,xpyn) reactions. The UNISOR isotope separator enabled mass identification. The previously unknown level scheme of136Pm was constructed and the half-life of136Sm was determined to be 47±2 s. Six new levels and thirteen newγ-ray transitions have been added to the level scheme of136Nd.