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Title: Lifetimes of low-lying excited states in Kr 50 36 86

Background: The evolution of nuclear magic numbers at extremes of isospin is a topic at the forefront of contemporary nuclear physics. N = 50 is a prime example, with increasing experimental data coming to light on potentially doubly magic Sn 100 and Ni 78 at the proton-rich and proton-deficient extremes, respectively; however, experimental discrepancies exist in the data for less exotic systems. Purpose: In Kr 86 the B ( E 2 ; 2 1 + 0 1 + ) value—a key indicator of shell evolution—has been experimentally determined by two different methodologies, with the results deviating by 3 σ . Here, we report on a new high-precision measurement of this value, as well as the first measured lifetimes and hence transition strengths for the 2 2 + and 3 ( 2 ) - states in the nucleus. Methods: The Doppler-shift attenuation method was implemented using the TRIUMF-ISAC γ -ray escape-suppressed spectrometer (TIGRESS) γ -ray spectrometer and the TIGRESS integrated plunger device. High-statistics Monte Carlo simulations were utilized to extract lifetimes in accordance with state-of-the-art methodologies. Results: Lifetimes of τ ( 2 1 + ) = 336 ± 4 (stat.) ± 20 (sys.) fs, τ ( 2 2 + ) = 263 ± 9 (stat.) ± 19 (sys.) fs, and τ ( 3 ( 2 ) - ) = 73 ± 6 (stat.) ± 32 (sys.) fs were extracted. This yields a transition strength for the first-excited state of B ( E 2 ; 2 1 + 0 1 + ) = 259 ± 3 (stat.) ± 16 (sys.) e 2 fm 4 . Conclusions: Finally, the measured lifetime disagrees with the previous Doppler-shift attenuation method measurement by more than 3 σ , while agreeing well with a previous value extracted from Coulomb excitation. The newly extracted B ( E 2 ; 2 1 + 0 1 + ) value indicates a more significant reduction in the N = 50 isotones approaching Z = 40 .
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [2] ;  [4] ;  [5] ;  [3] ;  [3] ;  [5] ;  [3] ;  [3] ;  [3] ;  [3] ;  [2] ;  [6] ;  [2]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); TRIUMF, Vancouver, BC (Canada)
  2. Simon Fraser Univ., Burnaby, BC (Canada). Dept. of Chemistry
  3. TRIUMF, Vancouver, BC (Canada)
  4. Univ. of Toronto, ON (Canada). Dept. of Physics
  5. TRIUMF, Vancouver, BC (Canada); Univ. of Surrey, Guildford (United Kingdom). Dept. of Physics
  6. Univ. of Guelph, ON (Canada). Dept. of Physics
Publication Date:
Report Number(s):
LLNL-JRNL-744244
Journal ID: ISSN 2469-9985
Grant/Contract Number:
AC52-07NA27344
Type:
Accepted Manuscript
Journal Name:
Physical Review C
Additional Journal Information:
Journal Volume: 97; Journal Issue: 4; Journal ID: ISSN 2469-9985
Publisher:
American Physical Society (APS)
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); TRIUMF, Vancouver, BC (Canada); Simon Fraser Univ., Burnaby, BC (Canada)
Sponsoring Org:
USDOE; Natural Sciences and Engineering Research Council of Canada (NSERC); The Canada Foundation for Innovation; British Columbia Knowledge Development Fund (Canada); National Research Council (NRC) (Canada)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; electromagnetic transitions; lifetimes & widths; nuclear structure & decays
OSTI Identifier:
1438625
Alternate Identifier(s):
OSTI ID: 1433278

Henderson, J., Chester, A., Ball, G. C., Caballero-Folch, R., Domingo, T., Drake, T. E., Evitts, L. J., Garnsworthy, A. B., Hackman, G., Hallam, S., Moukaddam, M., Ruotsalainen, P., Smallcombe, J., Smith, J. K., Starosta, K., Svensson, C. E., and Williams, J.. Lifetimes of low-lying excited states in Kr503686. United States: N. p., Web. doi:10.1103/PhysRevC.97.044311.
Henderson, J., Chester, A., Ball, G. C., Caballero-Folch, R., Domingo, T., Drake, T. E., Evitts, L. J., Garnsworthy, A. B., Hackman, G., Hallam, S., Moukaddam, M., Ruotsalainen, P., Smallcombe, J., Smith, J. K., Starosta, K., Svensson, C. E., & Williams, J.. Lifetimes of low-lying excited states in Kr503686. United States. doi:10.1103/PhysRevC.97.044311.
Henderson, J., Chester, A., Ball, G. C., Caballero-Folch, R., Domingo, T., Drake, T. E., Evitts, L. J., Garnsworthy, A. B., Hackman, G., Hallam, S., Moukaddam, M., Ruotsalainen, P., Smallcombe, J., Smith, J. K., Starosta, K., Svensson, C. E., and Williams, J.. 2018. "Lifetimes of low-lying excited states in Kr503686". United States. doi:10.1103/PhysRevC.97.044311.
@article{osti_1438625,
title = {Lifetimes of low-lying excited states in Kr503686},
author = {Henderson, J. and Chester, A. and Ball, G. C. and Caballero-Folch, R. and Domingo, T. and Drake, T. E. and Evitts, L. J. and Garnsworthy, A. B. and Hackman, G. and Hallam, S. and Moukaddam, M. and Ruotsalainen, P. and Smallcombe, J. and Smith, J. K. and Starosta, K. and Svensson, C. E. and Williams, J.},
abstractNote = {Background: The evolution of nuclear magic numbers at extremes of isospin is a topic at the forefront of contemporary nuclear physics. N=50 is a prime example, with increasing experimental data coming to light on potentially doubly magic Sn100 and Ni78 at the proton-rich and proton-deficient extremes, respectively; however, experimental discrepancies exist in the data for less exotic systems. Purpose: In Kr86 the B(E2;21+→01+) value—a key indicator of shell evolution—has been experimentally determined by two different methodologies, with the results deviating by 3σ. Here, we report on a new high-precision measurement of this value, as well as the first measured lifetimes and hence transition strengths for the 22+ and 3(2)- states in the nucleus. Methods: The Doppler-shift attenuation method was implemented using the TRIUMF-ISAC γ-ray escape-suppressed spectrometer (TIGRESS) γ-ray spectrometer and the TIGRESS integrated plunger device. High-statistics Monte Carlo simulations were utilized to extract lifetimes in accordance with state-of-the-art methodologies. Results: Lifetimes of τ(21+)=336±4(stat.)±20(sys.) fs, τ(22+)=263±9(stat.)±19(sys.) fs, and τ(3(2)-)=73±6(stat.)±32(sys.) fs were extracted. This yields a transition strength for the first-excited state of B(E2;21+→01+)=259±3(stat.)±16(sys.) e2 fm4. Conclusions: Finally, the measured lifetime disagrees with the previous Doppler-shift attenuation method measurement by more than 3σ, while agreeing well with a previous value extracted from Coulomb excitation. The newly extracted B(E2;21+→01+) value indicates a more significant reduction in the N=50 isotones approaching Z=40.},
doi = {10.1103/PhysRevC.97.044311},
journal = {Physical Review C},
number = 4,
volume = 97,
place = {United States},
year = {2018},
month = {4}
}