Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 47 (2014)

Study of the superallowed β-decay of 100 Sn
D. Lubos,∗1,∗2 M. Lewitowicz,∗3 R. Gernhäuser,∗1 R. Krücken,∗4 S. Nishimura,∗2 H. Sakurai,∗5 H. Baba,∗2
B. Blank,∗6 A. Blazhev,∗7 P. Boutachkov,∗8 F. Browne,∗9,∗2 I. Celikovic,∗3 P. Doornenbal,∗2 T. Faestermann,∗1Y. Fang,∗10,∗2 G. de France,∗3 N. Goel,∗8 M. Gorska,∗8 S. Ilieva,∗11 T. Isobe,∗2 A. Jungclaus,∗12 G. D. Kim,∗13Y.-K. Kim,∗13 I. Kojouharov,∗8 M. Kowalska,∗14 N. Kurz,∗8 Z. Li,∗15 G. Lorusso,∗2 K. Moschner,∗7I. Nishizuka,∗16,∗2 J. Park,∗4 Z. Patel,∗17,∗2 M. M. Rajabali,∗4 S. Rice,∗17,∗2 H. Schaffner,∗8 L. Sinclair,∗18,∗2P.-A. Söderström,∗2 K. Steiger,∗1 T. Sumikama,∗16 H. Watanabe,∗19 Z. Wang,∗4 J. Wu,∗12,∗2 and Z. Y. Xu∗5,∗2Proton Number Z

An experiment for studying the superallowed
Gamow-Teller decay of the doubly magic nucleus 100 Sn
was performed in June 2013 at the high-resolution separator BigRIPS of the RIBF at the RIKEN Nishina
Center. The β-decay of a g9/2 -proton in 100 Sn toa g7/2 -neutron in 100 In shows the smallest log(ft) =+0.13
value in the nuclear chart. The Gamow2.62−0.11+2.6, as deduced from theTeller strength BGT = 9.1−3.01)
last experiment at GSI . This value is consistent
with the results of BGT calculations as derived fromLSSM calculations. However, the uncertainties in theextracted BGT are still dominated by statistics. In
particular, the contribution of the β-decay end-point
energy Eβ,max amounts to 85% of the BGT uncertainty.
In the present experiment, a 4 mm Be target was bombarded with a 124 Xe beam of 345 MeV/u at intensities
up to 36.4 pnA to produce 100 Sn by fragmentation. Intotal, 2525 100 Sn ions (Fig. 1) were identified during 8.5
days of beamtime. This exceeds the number obtainedin the previous experiment at GSI1) by nearly a factorof 10, and the uncertainties in BGT are expected to
be improved by more than a factor of 2. Furthermore,
a number of nuclides towards the proton dripline havebeen newly identified (see Čeliković et al.2) ) and significantly higher statistics for N=Z and N=Z-1 isotopes
have been obtained.
In order to observe β- and γ-decays, 100 Sn and mostof the neighboring nuclei (see Fig. 1) were implanted
into the WAS3ABi detector, which is a closed stackconsisting of three highly segmented silicon detectorsof 1 mm thickness each surrounded by 84 Ge- and18 LaBr-detectors of the 4π-γ-spectrometer EURICA.
This WAS3ABi detector array is expanded by a stackof 10 silicon detectors of the same thickness in order51

Sn1001045049103481024746

1045
44

1.95

22.05

2.1

2.15

2.2
A/Q ratio

1Fig. 1. figure
PID plot in the region of 100 Sn. The total number of identified 100 Sn nuclei is 2525 (red encircled region).

to measure the total energy of the decay positrons accurately. Since Eβ,max = 3.29 ± 0.20 MeV is rathersmall1) , the decay positrons are stopped in the silicon
stack, enabling a high-precision measurement in order to determine Eβ,max . We find correlated β-decays
by considering decay events occurring within a time
window tc and active detector volume around the implantation. Thus, we can determine the half-lives ofβ-decays. From β-delayed γ-decays, using the largest
data sample on 100 Sn, we will be able to distinguishbetween two scenarios for the β-delayed γ-cascades toconfirm a dominantly populated 1+ state in 100 In afterβ-decay. Furthermore, we are looking for a 6+ isomericstate in 100 Sn, as predicted by Grawe et al.3) based on
LSSM calculations.
After a preliminary energy calibration of the WAS3ABidetectors, one of the most challenging tasks is to determine systematic uncertainties in the β-decay endpoint energy Eβ,max and β-half-life T1/2 . A small(systematic) error in these quantities affects the BGT ,resulting in a large relative uncertainty. Since 100 Sn
has a long half-life, the background contribution on
this measurement is also studied in detail to minimize
these systematic uncertainties.
First results indicate a good agreement withknown values1) of both quantities T1/2 (100 Sn) andEβ,max (100 Sn).

Physik Department E12, Technische Universität München
RIKEN Nishina Center∗3 GANIL∗4 TRIUMF∗5 Department of Physics, University of Tokyo∗6 CENBG∗7 Institut für Kernphysik, Universität zu Köln∗8 GSI Darmstadt∗9 School of Comp., Eng. and Maths., Brighton University∗10 Department of Physics, Osaka University∗11 Institut für Kernphysik, TU Darmstadt∗12 IES CSIS
∗13 Institute for Basic Science∗14 CERN∗15 School of Physics, Peking University∗16 Department of Physics, Tohoku University∗17 Department of Physics, Surrey University∗18 Department of Physics, University of York
∗19 Department of Physics, Beihang University∗1∗2References1) C. Hinke et al., Nature, 486, 341 (2012)2) I. Čeliković et al., RIKEN Acc. Prog. Rep., this volume3) H. Grawe et al., Eur. Phys. J. A 27, s01, 257 (2006)-7-