Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 53

Improved value for the Gamow-Teller strength of the 100 Sn beta-decay†
D. Lubos,∗1,∗2 J. Park,∗3 T. Faestermann,∗1 R. Gernhäuser,∗1 R. Krücken,∗4 M. Lewitowicz,∗5 S. Nishimura,∗2and H. Sakurai∗6 for the EURICA collaboration
The main aim of experiment NP0702-RIBF09 was toimprove the value for the Gamow-Teller strength of the100
Sn beta-decay. This is important because 100 Sn isthe heaviest self-conjugate doubly-magic nucleus. The
data have now been evaluated and published.
With about 2500 nuclei the number of detected
100Sn nuclei was about ten times higher than in previous experiments and new isotopic species towards theproton dripline were discovered at the RIKEN Nishina
Center.1)
Decay spectroscopy has been performed with thehigh-eﬃciency detector arrays WAS3ABi and EURICA. The half-life of 100 Sn was measured more precisely than the literature values2) using two methods:a) β-decays correlated with identiﬁed mother nucleiand b) correlated β-decays were in coincidence one ofthe known γ-rays following the beta-decay was observed. Both results agreed yielding an average ofT1/2 = 1.18 ± 0.08 s. This value agrees with and has
about half the error compared to the average of theprevious values.
Similarly, the β-decay endpoint energy was determined for two data sets, the β-spectrum after a 100 Sn
implantation and by requiring, in addition, a γ-ray
from the decay. The method was tested by analyzing also the 98 Cd decay Q-value. Both 100 Sn data
sets yielded consistent results which give as average
Qβ = 3.91 ± 0.15 MeV. This value is more precise andlarger than the best previous result2) by about twice
the summed error bars. This discrepancy may be due
to unaccounted systematic uncertainties in either measurement.
The value and the uncertainty of the resulting
strength for the pure 0+ → 1+ Gamow-Teller decay
is improved to BGT = 4.4+0.9−0.7 . In Fig. 1 we compare anumber of theoretical calculations of BGT with experimental values: an extrapolation of the BGT -values of
the heavier even-even Sn isotopes (the error bar seemstoo small) and the values measured in the two previous
experiments at GSI. Of all theories the chiral eﬀective
ﬁeld theory seems to describe the data best.

†∗1
∗2
∗3
∗4
∗5
∗6Fig. 1. Comparison of experimental and predicted GTtransition strengths of 100 Sn. The theoretical values
on the left side are from: Extreme Shell Model,3)Shell Model - Monte Carlo,4) Finite Fermi Systems andQuasiparticle Random Phase Approximation,5) Large
Scale Shell Model with transitions to the four and onelowest 1+ -states,2) the range of recent work explaining
GT-quenching with calculations using Eﬀective Field
Theory combined with 2-Body Currents.6) Experimental values are: an extrapolation from heavier even Snisotopes,7) ﬁrst8) and second2) GSI experiment, thepresent result and the average of all available experimental data. For the weighted average of Qβ its error
has been inﬂated by a factor 1.8 to account for the toolarge χ2 .

References

1) I. Celikovic et al., Phys. Rev. Lett. 116, 162501 (2016).
2) C. B. Hinke et al., Nature 486, 341 (2012), and Suppl.
Info.
3) A. de Shalit, I. Talmi, Nuclear Shell Theory (Aca- demicPress, New York and London, 1963).
4) D. Dean, S. Koonin, T. Kuo, K. Langanke, P. Radha,Phys. Lett. B 367, 17 (1996).
5) A. Bobyk, W. Kaminski, Acta Phys. Pol. B 31, 953(2000).
6) P. Gysbers et al., Nature Phys. 15, 428 (2019).
7) L. Batist et al., Eur. Phys. J. A 46, 45 (2010).
8) T. Faestermann et al., Eur. Phys. J. A 15, 185 (2002).

Condensed from the article in Phys. Rev. Lett. 122, 222502(2019)
Technische Universität München
RIKEN Nishina Center
Lund University
TRIUMFGANIL, CEA/DSM-CNRS/IN2P3
University of Tokyo- 32 -