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Beta-decay Half Lives beyond $^{54}$Ca: A Systematic Survey of Decay Properties approaching the Neutron Dripline

W. -J. Ong, Z. Y. Xu, R. Grzywacz, A. Ravlić, I. Cox, J. M. Allmond, T. T. King, B. C. Rasco, K. P. Rykaczewski, H. Schatz, B. M. Sherrill, B. Tarasov, B. A. Brown, S. Ajayi, H. Arora, A. D. Ayangeakaa, H. C. Berg, J. M. Berkman, D. L. Bleuel, K. Bosmpotinis, M. P. Carpenter, G. Cerizza, A. Chester, J. M. Christie, H. L. Crawford, B. P. Crider, J. Davis, A. A. Doetsch, J. G. Duarte, A. Estrade, A. Fijalkowska, C. Frantzis, K. Fukushima, T. Gaballah, T. Gray, E. Good, K. Haak, S. Hanai, A. C. Hartley, J. T. Harke, K. Hermansen, C. Harris, M. Hausmann, D. E. M. Hoff, D. Hoskins, J. Huffman, R. Jain, M. Karny, N. Kitamura, K. Kolos, E. Kwan, A. Laminack, S. N. Liddick, B. Longfellow, R. S. Lubna, S. Lyons, M. Madurga, M. Mogannam, S. Neupane, A. Nowicki, T. H. Ogunbeku, G. Owens-Fryar, J. R. Palomino, M. Portillo, M. M. Rajabali, A. L. Richard, I. Richardson, E. Ronning, G. E. Rose, T. Ruland, N. D. Scielzo, D. P. Scriven, D. Seweryniak, K. Siegl, M. Singh, M. K. Smith, A. Spyrou, M. Stepaniuk, A. Sweet, V. Tripathi, A. Tsantiri, S. Uthayakumaar, W. B. Walters, S. Watters, M. Wolinska-Cichocka, R. Yokoyama

Abstract

In an experiment performed at the Facility for Rare Isotope Beams (FRIB) using the FRIB Decay Station initiator (FDSi), 15 new half lives of isotopes near $^{54}$Ca were measured. A new method of extracting lifetimes from experimental data, taking into account the unknown $β$-delayed neutron emission branches of very neutron-rich nuclei, was developed to enable systematic uncertainty analysis. The experiment observed a dramatic change in the half-life systematics for the isotopes with neutron number N =34. Beyond N =34, the decline of nuclear lifetime is much slower, leading to longer than anticipated lifetimes for near-dripline nuclei. State-of-the-art shell-model calculations can explain the experimental results for Z$>$19 nuclei, revealing the imprint of shell effects and the need for modification of single-particle neutron states. The results from a newly developed QRPA model with potential for making global predictions were also tested against the experimental results and good agreement was found.

Beta-decay Half Lives beyond $^{54}$Ca: A Systematic Survey of Decay Properties approaching the Neutron Dripline

Abstract

In an experiment performed at the Facility for Rare Isotope Beams (FRIB) using the FRIB Decay Station initiator (FDSi), 15 new half lives of isotopes near Ca were measured. A new method of extracting lifetimes from experimental data, taking into account the unknown -delayed neutron emission branches of very neutron-rich nuclei, was developed to enable systematic uncertainty analysis. The experiment observed a dramatic change in the half-life systematics for the isotopes with neutron number N =34. Beyond N =34, the decline of nuclear lifetime is much slower, leading to longer than anticipated lifetimes for near-dripline nuclei. State-of-the-art shell-model calculations can explain the experimental results for Z19 nuclei, revealing the imprint of shell effects and the need for modification of single-particle neutron states. The results from a newly developed QRPA model with potential for making global predictions were also tested against the experimental results and good agreement was found.
Paper Structure (5 figures, 1 table)

This paper contains 5 figures, 1 table.

Figures (5)

  • Figure 1: Particle identification plot showing proton number $Z$ and mass-to-charge ratio $A/Q$ for the cocktail beam delivered to the first focal plane of the FDSi. Nuclei with previously unreported half lives are located to the right of the red line. The $A/Q$ = 2.7 nucleus $^{54}$Ca is labeled.
  • Figure 2: Top: Decay curve $^{59}$Sc showing the different components of the fit. Bottom: The 2-D posterior distributions of the fit parameters for $^{59}$Sc.
  • Figure 3: Half-life systematics of neutron-rich isotopes from chlorine ($Z=17$) to titanium ($Z=22$). The experimental data are compared with FRDM+QRPA moller2019, RHB+pnRQRPA marketin2016, PCpnRQRPA, and LSSM with the sdpf-mu and ufp-ca interactions.
  • Figure 4: Schematic drawing of the dominant GT channels in the systematics of $^{49-60}$Ca.
  • Figure 5: Decay curves for $^{48-51}$Cl, $^{51-53}$Ar, $^{55}$K, $^{57,58}$Ca, $^{59-61}$Sc, and $^{62,63}$Ti. The fits include the decays of the parent nucleus (solid blue), daughter (green solid), sum of neutron daughters (purple solid), and granddaughter (orange solid). The flat background from random correlations is obtained from the time-inverse correlations (black dashed). The total fit is given by the red solid line.