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Nuclear Data Sheets for A = 168

Nuclear structure data pertaining to all nuclei with mass A=168 (Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt) have been evaluated and incorporated into the ENSDF data file. This evaluation supersedes the previous publication (V.S. Shirley, Nuclear Data Sheets 71, 261 (1994) (literature cutoff date July 1993)) and subsequent ENSDF file revisions for Tb and Dy (C. Baglin, literature cutoff date of 15 June 1999) and Hf (B. Singh, literature cutoff date of 30 April 2001), and includes literature available by 15 June 2010. Since the above evaluations, the first excited states in {sup 168}Pt have been identified (1998Ki20, 2009Go16) and {alpha} decay from {sup 172}Hg has been observed (2009Sa27, 2004Ke06, 1999Se14). New levels in {sup 168}Dy have been excited using the {sup 170}Er({sup 82}Se,{sup 84}Kr{gamma}) reaction (2010So03). (HI,xn{gamma}) studies have significantly expanded our knowledge of level structure in {sup 168}Lu (1999Ka17, 2002Ha33), {sup 168}Ta (2008QiZZ), {sup 168}Yb (1995Fi01), {sup 168}Tm (2007CaZW), {sup 168}Hf (2009Ya21), {sup 168}Os (2001Jo11, 2009Od02) and, for {sup 168}Tm, important information has come also from (d,2n{gamma}) and ({alpha},n{gamma}) reactions (1995Si20). Revised decay schemes are available following new studies of {sup 168}Hf {epsilon} decay (6.7 min) (1997Ba26), {sup 168}Lu {epsilon} decay (1999Ba65), {sup 168}Ta {epsilon} decay (2007Mc08) and {sup 172}Au {alpha} decay (2009Ha42). Significant new information for {sup 168}Er is available from (p,t) (2006Bu09), (d,p) and (t,d) (1996Ma50), ({gamma},{gamma}') (1996Ma18), (136Xe, X{gamma}) (2010Dr02), ({sup 238}U,{sup 238}U{sup '{gamma}}) (2003Wu07) and (n,n{sup '{gamma}}) (1998Be20, 1998Be62) reactions, and the availability of {gamma}{gamma} coin data (1994Ju02, 1996Gi09) for the (n,{gamma}) E=thermal reaction has resulted in some significant level scheme revisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Two-quasiparticle structures and isomers in {sup 168}Er, {sup 170}Er, and {sup 172}Er

The stable and neutron-rich isotopes {sup 168}Er, {sup 170}Er, and {sup 172}Er have been studied with Gammasphere using inelastic excitation with energetic {sup 136}Xe beams. The previously assigned structures based on the proposed K{sup p}i=4{sup -} isomeric intrinsic states in both {sup 168}Er and {sup 170}Er have been re-evaluated and an equivalent band identified in {sup 172}Er. In {sup 170}Er, the identification of a K{sup p}i=6{sup -} band with transitions close in energy to those of the 4{sup -} band leads to a modified interpretation, since the overlap would have compromised previous analyses. The g{sub K}-g{sub R} values for the 4{sup -} bands deduced from the in-band gamma-ray intensities for the sequence of isotopes suggest a predominantly two-neutron configuration in {sup 168}Er, an equally mixed two-neutron, two-proton configuration in {sup 170}Er, and a two-proton configuration in {sup 172}Er. A comprehensive decay scheme for the previously proposed 6{sup +} isomer in {sup 172}Er has also been established, as well as band structures built on this isomer that closely resemble the 6{sup +} and 7{sup -} two-neutron structures known in the isotone {sup 174}Yb. The implied K hindrances are discussed. The main decay path of the 6{sup +} isomer occurs through the newly identified 4{sup -} isomer. The measured lifetimes of the 4{sup -} and 6{sup +} isomers in {sup 172}Er are 57(3) and 822(90) ns, respectively. Multiquasiparticle calculations support the suggested configuration changes across the isotopic chain.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Q values for neutrinoless double-electron capture in {sup 96}Ru, {sup 162}Er, and {sup 168}Yb

The Q values of the neutrinoless double-electron capture transitions in {sup 96}Ru, {sup 162}Er, and {sup 168}Yb have been determined by Penning-trap mass-ratio measurements. Based on our new high-precision results for the Q values, neither of these transitions shows a resonant enhancement of the capture rate. At present, this excludes these nuclides from the list of suitable candidates in the search for neutrinoless double-electron capture.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗