J.M. Nitschke

Evidence for the possible synthesis of element 110 produced by the {sup 59}Co+{sup 209}Bi reaction

An experiment to synthesize element 110 by the {sup 59}Co+{sup 209}Bi reaction has been performed at the SuperHILAC at the Lawrence Berkeley Laboratory. One event with many of the expected characteristics of a successful synthesis of {sup 267}110 was observed. This event corresponds to a production cross section of about one picobarn.

Evidence for the synthesis of 267110 produced by the 59Co+209Bi reaction

Abstract An experiment to synthesize element 110 by the 59 Co+ 209 Bi reaction has been performed at the SuperHILAC at the Lawrence Berkeley Laboratory. One event with many of the expected characteristics of a successful synthesis of 267 110 was observed. This event corresponds to a production cross section of about one picobarn.

SEARCH FOR AN 80-ms SPONTANEOUS FISSION ACTIVITY IN BOMBARDMENTS OF 249Bk WITH 15N

Nitschke, M Fowler, A. Nurmia, .L. P. Somerville, Landrum, . W,. Lo!Jghee{;\, J, Silva, .and Eskola TWO-WEEK LOAN COPY This is a Library Circulating Copy wh may be borrowed two weeks. For a personal retention copyy call Divisiony Ext 6782. Preoan~d for the U.S. Department of Energy under Contract W-1405-ENG-48

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.

Spectroscopic studies near the proton drip line

We have investigated nuclei close to the proton drip line by using heavy‐ion fusion reactions to produce extremely neutron‐deficient nuclides. Their nuclear decay properties were studied by using on‐line isotope separators at Oak Ridge (UNISOR) and Berkeley (OASIS), the Oak Ridge National Laboratory velocity filter, and a fast helium‐gas‐jet transport system at Lawrence Berkeley Laboratory 88‐inch Cyclotron. Many isotopes, isomers, and β‐delayed‐proton and α‐particle emitters were discovered. This contribution summarizes three topics that are part of our overall program: (a) decay rates of even‐even α‐particle emitters, (b) mass excesses of 181Pb, 182Pb, and 183Pb, and (c) β‐delayed proton emitters near N=82.

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.

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 [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.

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.