Title: Lifetimes of low-lying excited states in ${}_{36}{}^{86}\mathrm{Kr}_{50}$

Abstract

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 ${}_{100}\mathrm{Sn}$ and ${}_{78}\mathrm{Ni}$ at the proton-rich and proton-deficient extremes, respectively; however, experimental discrepancies exist in the data for less exotic systems. Purpose: In ${}_{86}\mathrm{Kr}$ the $B(E2;2_1^{+}\to 0_1^{+})$ value—a key indicator of shell evolution—has been experimentally determined by two different methodologies, with the results deviating by $3\sigma$. 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 $3_{\left(2\right)}^{-}$ states in the nucleus. Methods: The Doppler-shift attenuation method was implemented using the TRIUMF-ISAC $\gamma$-ray escape-suppressed spectrometer (TIGRESS) $\gamma$-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 $\tau \left(2_1^{+}\right)=336\pm 4\text{(stat.)}\pm 20\text{(sys.)}$ fs, $\tau \left(2_2^{+}\right)=263\pm 9\text{(stat.)}\pm 19\text{(sys.)}$ fs, and $\tau \left(3_{\left(2\right)}^{-}\right)=73\pm 6\text{(stat.)}\pm 32\text{(sys.)}$ fs were extracted. This yields a transition strength for the first-excited state of $B(E2;2_1^{+}\to 0_1^{+})=259\pm 3\text{(stat.)}\pm 16\text{(sys.)}$ $e^2$ ${\mathrm{fm}}^4$. Conclusions: Finally, the measured lifetime disagrees with the previous Doppler-shift attenuation method measurement by more than $3\sigma$, while agreeing well with a previous value extracted from Coulomb excitation. The newly extracted $B(E2;2_1^{+}\to 0_1^{+})$ value indicates a more significant reduction in the $N=50$ isotones approaching $Z=40$.

Authors:

Henderson, J. ^[1]; Chester, A. ^[2]; Ball, G. C. ^[3]; Caballero-Folch, R. ^[3]; Domingo, T. ^[2]; Drake, T. E. ^[4]; Evitts, L. J. ^[5]; Garnsworthy, A. B. ^[3]; Hackman, G. ^[3]; Hallam, S. ^[5]; Moukaddam, M. ^[3]; Ruotsalainen, P. ^[3]; Smallcombe, J. ^[3]; Smith, J. K. ^[3]; Starosta, K. ^[2]; Svensson, C. E. ^[6]; Williams, J. ^[2]

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+ Show Author Affiliations

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:

Mon Apr 16 00:00:00 EDT 2018

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)

OSTI Identifier:

1438625

Alternate Identifier(s):

OSTI ID: 1433278

Report Number(s):

LLNL-JRNL-744244
Journal ID: ISSN 2469-9985; TRN: US1900471

Grant/Contract Number:  

AC52-07NA27344

Resource Type:

Journal Article: 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)

Country of Publication:

United States

Language:

English

Subject:

73 NUCLEAR PHYSICS AND RADIATION PHYSICS; electromagnetic transitions; lifetimes & widths; nuclear structure & decays