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Title: Novel Δ J = 1 Sequence in Ge 78 : Possible Evidence for Triaxiality

Abstract

Here, a sequence of low-energy levels in 78 32Ge 46 has been identified with spins and parity of 2 +, 3 +, 4 +, 5 +, and 6 +. Decays within this band proceed strictly through ΔJ=1 transitions, unlike similar sequences in neighboring Ge and Se nuclei. Above the 2+ level, members of this sequence do not decay into the ground-state band. Moreover, the energy staggering of this sequence has the phase that would be expected for a γ-rigid structure. The energies and branching ratios of many of the levels are described well by shell-model calculations. However, the calculated reduced transition probabilities for the ΔJ=2 in-band transitions imply that they should have been observed, in contradiction with the experiment. Within the calculations of Davydov, Filippov, and Rostovsky for rigid-triaxial rotors with γ=30°, there are sequences of higher-spin levels connected by strong ΔJ=1 transitions which decay in the same manner as those observed experimentally, yet are calculated at too high an excitation energy.

Authors:
 [1];  [1];  [2];  [3];  [4];  [1];  [5];  [6];  [7];  [8];  [7];  [7];  [7];  [7];  [9];  [10];  [9];  [7];  [5];  [7]
  1. Univ. of Maryland, College Park, MD (United States)
  2. Univ. of Maryland, College Park, MD (United States); Argonne National Lab. (ANL), Argonne, IL (United States); U.S. Army Research Lab., Adelphi, MD (United States)
  3. Argonne National Lab. (ANL), Argonne, IL (United States); Univ. of North Carolina, Chapel Hill, NC (United States)
  4. Argonne National Lab. (ANL), Argonne, IL (United States); United States Naval Academy, Annapolis, MD (United States)
  5. Univ. of Maryland, College Park, MD (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
  6. Argonne National Lab. (ANL), Argonne, IL (United States); TRIUMF, Vancouver, BC (Canada)
  7. Argonne National Lab. (ANL), Argonne, IL (United States)
  8. Argonne National Lab. (ANL), Argonne, IL (United States); Millsaps College, Jackson, MS (United States)
  9. Argonne National Lab. (ANL), Argonne, IL (United States); Univ. of Massachusetts, Lowell, MA (United States)
  10. Argonne National Lab. (ANL), Argonne, IL (United States); Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26); USDOE Office of Science - Office of Nuclear Physics
OSTI Identifier:
1438428
Alternate Identifier(s):
OSTI ID: 1438290; OSTI ID: 1493714
Report Number(s):
BNL-203652-2018-JAAM; BNL-203358-2018-JAAM
Journal ID: ISSN 0031-9007; PRLTAO; TRN: US1900437
Grant/Contract Number:  
SC0012704; AC02-06CH11357; AC02-98CH10886; FG02-94ER40834; FG02-97ER41041; FG02-97ER41033
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 120; Journal Issue: 21; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS

Citation Formats

Forney, A. M., Walters, W. B., Chiara, C. J., Janssens, R. V. F., Ayangeakaa, A. D., Sethi, J., Harker, J., Alcorta, M., Carpenter, M. P., Gurdal, G., Hoffman, C. R., Kay, B. P., Kondev, F. G., Lauritsen, T., Lister, C. J., McCutchan, Elizabeth A., Rogers, A. M., Seweryniak, D., Stefanescu, I., and Zhu, S. Novel ΔJ=1 Sequence in Ge78: Possible Evidence for Triaxiality. United States: N. p., 2018. Web. doi:10.1103/PhysRevLett.120.212501.
Forney, A. M., Walters, W. B., Chiara, C. J., Janssens, R. V. F., Ayangeakaa, A. D., Sethi, J., Harker, J., Alcorta, M., Carpenter, M. P., Gurdal, G., Hoffman, C. R., Kay, B. P., Kondev, F. G., Lauritsen, T., Lister, C. J., McCutchan, Elizabeth A., Rogers, A. M., Seweryniak, D., Stefanescu, I., & Zhu, S. Novel ΔJ=1 Sequence in Ge78: Possible Evidence for Triaxiality. United States. doi:10.1103/PhysRevLett.120.212501.
Forney, A. M., Walters, W. B., Chiara, C. J., Janssens, R. V. F., Ayangeakaa, A. D., Sethi, J., Harker, J., Alcorta, M., Carpenter, M. P., Gurdal, G., Hoffman, C. R., Kay, B. P., Kondev, F. G., Lauritsen, T., Lister, C. J., McCutchan, Elizabeth A., Rogers, A. M., Seweryniak, D., Stefanescu, I., and Zhu, S. Tue . "Novel ΔJ=1 Sequence in Ge78: Possible Evidence for Triaxiality". United States. doi:10.1103/PhysRevLett.120.212501. https://www.osti.gov/servlets/purl/1438428.
@article{osti_1438428,
title = {Novel ΔJ=1 Sequence in Ge78: Possible Evidence for Triaxiality},
author = {Forney, A. M. and Walters, W. B. and Chiara, C. J. and Janssens, R. V. F. and Ayangeakaa, A. D. and Sethi, J. and Harker, J. and Alcorta, M. and Carpenter, M. P. and Gurdal, G. and Hoffman, C. R. and Kay, B. P. and Kondev, F. G. and Lauritsen, T. and Lister, C. J. and McCutchan, Elizabeth A. and Rogers, A. M. and Seweryniak, D. and Stefanescu, I. and Zhu, S.},
abstractNote = {Here, a sequence of low-energy levels in 7832Ge46 has been identified with spins and parity of 2+, 3+, 4+, 5+, and 6+. Decays within this band proceed strictly through ΔJ=1 transitions, unlike similar sequences in neighboring Ge and Se nuclei. Above the 2+ level, members of this sequence do not decay into the ground-state band. Moreover, the energy staggering of this sequence has the phase that would be expected for a γ-rigid structure. The energies and branching ratios of many of the levels are described well by shell-model calculations. However, the calculated reduced transition probabilities for the ΔJ=2 in-band transitions imply that they should have been observed, in contradiction with the experiment. Within the calculations of Davydov, Filippov, and Rostovsky for rigid-triaxial rotors with γ=30°, there are sequences of higher-spin levels connected by strong ΔJ=1 transitions which decay in the same manner as those observed experimentally, yet are calculated at too high an excitation energy.},
doi = {10.1103/PhysRevLett.120.212501},
journal = {Physical Review Letters},
number = 21,
volume = 120,
place = {United States},
year = {2018},
month = {5}
}

Journal Article:
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Figures / Tables:

FIG. 1 FIG. 1: (Color online). Coincidence spectra from the multinucleon transfer reaction of 76Ge + 238U with 78Ge γ peaks labelled by their energies in keV. (a) Spectrum with a double gate placed on the 950.6-keV 4$^+_1$ → 2$^+_1$ and the 619.2-keV 2$^+_1$ → 0$^+_1$ transitions. (b) Spectrum in coincidence withmore » the 619.2-keV ground-state transition and the 567.1-keV γ ray linking the 2$^+_κ$ and 2$^+_1$ states. The inset in (b) is an enlargement meant to indicate the absence of the ΔJ = 2 crossover transitions discussed in the text. Their locations are indicated by the expected transition energies marked on-line in green. Note that, while very weak, the 976-keV peak is associated with a contaminant transition in another nucleus. The 78Ge peaks identified in these spectra with an * do not appear in the partial level scheme shown in Fig. 2. The green triangles in both spectra mark a transition from the 76Ge beam, while the diamonds correspond to γ rays from the 238U target. A red square marks the positron annihilation peak.« less

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    Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.