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Coulomb excitation of a Am-242 isomeric target: E2 and E3 strengths, rotational alignment, and collective enhancement

Hayes, A. B.; Cline, D.; Moody, K. J.; Ragnarsson, Ingemar LU ; Wu, C. Y.; Becker, J. A.; Carpenter, M. P.; Carroll, J. J.; Gohlke, D. and Greene, J. P., et al. (2010) In Physical Review C (Nuclear Physics) 82(4).
Abstract
A 98% pure Am-242m ( K = 5(-), t(1/2) = 141 years) isomeric target was Coulomb excited with a 170.5-MeV Ar-40 beam. The selectivity of Coulomb excitation, coupled with the sensitivity of Gammasphere plus CHICO, was sufficient to identify 46 new states up to spin 18h in at least four rotational bands; 11 of these new states lie in the isomer band, 13 in a previously unknown yrast K-pi = 6(-) rotational band, and 13 in a band tentatively identified as the predicted yrast K-pi = 5(+) band. The rotational bands based on the K-pi = 5- isomer and the 6(-) bandhead were populated by Coulomb excitation with unexpectedly equal cross sections. The gamma-ray yields are reproduced by Coulomb excitation calculations using a two-particle plus rotor... (More)
A 98% pure Am-242m ( K = 5(-), t(1/2) = 141 years) isomeric target was Coulomb excited with a 170.5-MeV Ar-40 beam. The selectivity of Coulomb excitation, coupled with the sensitivity of Gammasphere plus CHICO, was sufficient to identify 46 new states up to spin 18h in at least four rotational bands; 11 of these new states lie in the isomer band, 13 in a previously unknown yrast K-pi = 6(-) rotational band, and 13 in a band tentatively identified as the predicted yrast K-pi = 5(+) band. The rotational bands based on the K-pi = 5- isomer and the 6(-) bandhead were populated by Coulomb excitation with unexpectedly equal cross sections. The gamma-ray yields are reproduced by Coulomb excitation calculations using a two-particle plus rotor model (PRM), implying nearly complete Delta K = 1 mixing of the two almost-degenerate rotational bands, but recovering the Alaga rule for the unperturbed states. The degeneracy of the 5(-) and 6(-) bands allows for precise determination of the mixing interaction strength V, which approaches the strong-mixing limit; this agrees with the 50% attenuation of the Coriolis matrix element assumed in the model calculations. The fractional admixture of the I-K(pi) = 6(6)(-) state in the nominal 6(5)(-) isomer band state is measured within the PRM as 45.6(-1.1)(+0.3)%. The E2 and M1 strengths coupling the 5(-) and 6(-) bands are enhanced significantly by the mixing, while E1 and E2 couplings to other low-K bands are not measurably enhanced. The yields of the 5(+) band are reproduced by an E3 strength of approximate to 15 W.u., competitive with the interband E2 strength. Alignments of the identified two-particle Nilsson states in Am-242 are compared with the single-particle alignments in Am-241. (Less)
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Physical Review C (Nuclear Physics)
volume
82
issue
4
publisher
American Physical Society
external identifiers
  • wos:000283648400004
  • scopus:78649361028
ISSN
0556-2813
DOI
10.1103/PhysRevC.82.044319
language
English
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yes
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655e1c14-121b-4cd2-9037-bba14bd2fca2 (old id 1752979)
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2010-12-29 15:31:12
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2018-05-29 12:29:52
@article{655e1c14-121b-4cd2-9037-bba14bd2fca2,
  abstract     = {A 98% pure Am-242m ( K = 5(-), t(1/2) = 141 years) isomeric target was Coulomb excited with a 170.5-MeV Ar-40 beam. The selectivity of Coulomb excitation, coupled with the sensitivity of Gammasphere plus CHICO, was sufficient to identify 46 new states up to spin 18h in at least four rotational bands; 11 of these new states lie in the isomer band, 13 in a previously unknown yrast K-pi = 6(-) rotational band, and 13 in a band tentatively identified as the predicted yrast K-pi = 5(+) band. The rotational bands based on the K-pi = 5- isomer and the 6(-) bandhead were populated by Coulomb excitation with unexpectedly equal cross sections. The gamma-ray yields are reproduced by Coulomb excitation calculations using a two-particle plus rotor model (PRM), implying nearly complete Delta K = 1 mixing of the two almost-degenerate rotational bands, but recovering the Alaga rule for the unperturbed states. The degeneracy of the 5(-) and 6(-) bands allows for precise determination of the mixing interaction strength V, which approaches the strong-mixing limit; this agrees with the 50% attenuation of the Coriolis matrix element assumed in the model calculations. The fractional admixture of the I-K(pi) = 6(6)(-) state in the nominal 6(5)(-) isomer band state is measured within the PRM as 45.6(-1.1)(+0.3)%. The E2 and M1 strengths coupling the 5(-) and 6(-) bands are enhanced significantly by the mixing, while E1 and E2 couplings to other low-K bands are not measurably enhanced. The yields of the 5(+) band are reproduced by an E3 strength of approximate to 15 W.u., competitive with the interband E2 strength. Alignments of the identified two-particle Nilsson states in Am-242 are compared with the single-particle alignments in Am-241.},
  articleno    = {044319},
  author       = {Hayes, A. B. and Cline, D. and Moody, K. J. and Ragnarsson, Ingemar and Wu, C. Y. and Becker, J. A. and Carpenter, M. P. and Carroll, J. J. and Gohlke, D. and Greene, J. P. and Hecht, A. A. and Janssens, R. V. F. and Karamian, S. A. and Lauritsen, T. and Lister, C. J. and Macri, R. A. and Propri, R. and Seweryniak, D. and Wang, X. and Wheeler, R. and Zhu, S.},
  issn         = {0556-2813},
  language     = {eng},
  number       = {4},
  publisher    = {American Physical Society},
  series       = {Physical Review C (Nuclear Physics)},
  title        = {Coulomb excitation of a Am-242 isomeric target: E2 and E3 strengths, rotational alignment, and collective enhancement},
  url          = {http://dx.doi.org/10.1103/PhysRevC.82.044319},
  volume       = {82},
  year         = {2010},
}