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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