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

Journal Article · Fri Oct 15 00:00:00 EDT 2010 · Physical Review. C, Nuclear Physics

DOI:https://doi.org/10.1103/PHYSREVC.82.044319· OSTI ID:21419609

Hayes, A B; Cline, D ^[1]; Moody, K J; Wu, C Y; Becker, J A; Macri, R A ^[2]; Ragnarsson, I ^[3]; Carpenter, M P; Greene, J P; Janssens, R V. F.; Lauritsen, T; Lister, C J; Seweryniak, D; Wang, X; Zhu, S ^[4]; Carroll, J J; Gohlke, D; Propri, R; Wheeler, R ^[5]; Hecht, A A ^[4]

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1. Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627 (United States)
2. Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
3. Department of Mathematical Physics, Lund Institute of Technology, SE-221 00 Lund (Sweden)
4. Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
5. Department of Physics and Astronomy, Youngstown State University, Youngstown, Ohio 44555 (United States)

A 98% pure {sup 242m}Am (K=5{sup -}, t{sub 1/2}=141 years) isomeric target was Coulomb excited with a 170.5-MeV {sup 40}Ar beam. The selectivity of Coulomb excitation, coupled with the sensitivity of Gammasphere plus CHICO, was sufficient to identify 46 new states up to spin 18({h_bar}/2{pi}) in at least four rotational bands; 11 of these new states lie in the isomer band, 13 in a previously unknown yrast K{sup {pi}=}6{sup -} rotational band, and 13 in a band tentatively identified as the predicted yrast K{sup {pi}=}5{sup +} band. The rotational bands based on the K{sup {pi}=}5{sup -} isomer and the 6{sup -} 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{sup -} and 6{sup -} 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{sub K}{sup {pi}=}6{sub 6}{sup -} state in the nominal 6{sub 5}{sup -} isomer band state is measured within the PRM as 45.6{sub -1.1}{sup +0.3}%. The E2 and M1 strengths coupling the 5{sup -} and 6{sup -} 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{sup +} band are reproduced by an E3 strength of {approx_equal}15 W.u., competitive with the interband E2 strength. Alignments of the identified two-particle Nilsson states in {sup 242}Am are compared with the single-particle alignments in {sup 241}Am.

• OSTI ID: 21419609
• Journal Information: Physical Review. C, Nuclear Physics, Vol. 82, Issue 4; Other Information: DOI: 10.1103/PhysRevC.82.044319; (c) 2010 The American Physical Society; ISSN 0556-2813
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
AMERICIUM 241
AMERICIUM 242 TARGET
ARGON 40
BEAMS
COULOMB EXCITATION
COUPLING
CROSS SECTIONS
GAMMA RADIATION
INTERACTIONS
ISOMERS
MATRIX ELEMENTS
MEV RANGE 100-1000
MIXING
ROTATIONAL STATES
SENSITIVITY
SPIN
ACTINIDE NUCLEI
ALPHA DECAY RADIOISOTOPES
AMERICIUM ISOTOPES
ANGULAR MOMENTUM
ARGON ISOTOPES
ELECTROMAGNETIC RADIATION
ENERGY LEVELS
ENERGY RANGE
ENERGY-LEVEL TRANSITIONS
EVEN-EVEN NUCLEI
EXCITATION
EXCITED STATES
HEAVY NUCLEI
IONIZING RADIATIONS
ISOTOPES
LIGHT NUCLEI
MEV RANGE
NUCLEI
ODD-EVEN NUCLEI
PARTICLE PROPERTIES
RADIATIONS
RADIOISOTOPES
SPONTANEOUS FISSION RADIOISOTOPES
STABLE ISOTOPES
TARGETS
YEARS LIVING RADIOISOTOPES