RIKEN Accel. Prog. Rep. 48 (2015)

Ⅰ. HIGHLIGHTS OF THE YEAR

Intermediate-energy Coulomb excitation of 104Sn:
Moderate E2 strength decrease approaching 100 Sn†
P. Doornenbal,∗1 S. Takeuchi,∗1 N. Aoi,∗2 M. Matsushita,∗3,∗4 A. Obertelli,∗5 D. Steppenbeck,∗3 H. Wang,∗1,∗6L. Audirac,∗5 H. Baba,∗1 P. Bednarczyk,∗7 S. Boissinot,∗5 M. Ciemala,∗7 A. Corsi,∗5 T. Furumoto,∗8 T. Isobe,∗1A. Jungclaus,∗9 V. Lapoux,∗5 J. Lee,∗1 K. Matsui,∗10 T. Motobayashi,∗1 D. Nishimura,∗11 S. Ota,∗3E.C. Pollacco,∗5 H. Sakurai,∗1,∗10 C. Santamaria,∗5 Y. Shiga,∗4 D. Sohler,∗12 and R. Taniuchi∗10Counts / 25 keV

In recent years, several experimental findings generated a large interest regarding the E2 strength patternin the tin isotopes. While the neutron-rich isotopes
with A = 126, 128, 130 follow the anticipated trend ofsmoothly decreasing B(E2)↑ values towards the major
shell closure well described by large-scale shell-model(LSSM) calculations1,2) , the proton-rich nuclei take adifferent path. Commencing with the stable A = 114isotope a steadily growing deviation from the shellmodel expectations was observed with almost constantB(E2)↑ values for the A = 106 − 112 isotopes1–3) . A
first attempt for 104 Sn with limited statistics has recently been made4) . The result of 0.10(4) e2 b2 indicates a steep decrease of excitation strength in agreement with LSSM calculations. In a second measurement, a considerably larger value of 0.180(37) e2 b2 wasobtained5) . Here, we report on the first B(E2)↑ extraction of 104 Sn from absolute Coulomb excitation crosssections at intermediate energies.
A 124 Xe primary beam was accelerated up to an energy of 345 MeV/nucleon and impinged on a 3 mm
thick Be production target at the F0 focus of the BigRIPS fragment separator6). The Bρ − ∆E − Bρ
method was applied to select and purify secondary
beams of 104 Sn and 112 Sn in two subsequent measurements. The secondary beams were transported to thefocal point F8, where a 557 mg/cm2 thick Pb target
was inserted to induce Coulomb excitation reactions.
+To detect γ-rays from the 2+
1 → 0gs transitions, thereaction target was surrounded by the DALI2 array7).
Reaction products were identified behind the reaction
target by the ZeroDegree spectrometer1) .
A B(E2)↑ value of 0.173(28) e2 b2 was deduced for104
Sn. The run with 112 Sn, which has a known B(E2)↑800

Experiment
Simulation 1253 keV
Background Fit
Sim. + Backgrounda)

600*Pb(112Sn,112Sn )400

Counts / 25 keV

200

300

Experiment
Simulation 1258 keV
Background Fit
Sim. + Backgroundb)

200*Pb(104Sn,104Sn )

100
500

1000

1500

2000 2500 3000
Energy (keV)

Fig. 1. Doppler corrected γ-ray spectra of 112 Sn (top panel+a) and 104 Sn (bottom panel b). The observed 2+1 → 0gs
transitions are compared to simulations.

value, was used for feeding estimations. Our result
is in agreement with the 0.180(37) e2 b2 obtained inRef.5) with largely overlapping error bars, but deviates significantly from the value of 0.10(4) e2 b2 obtained in Ref.4) . The drop in excitation strength ismuch smoother than suggested in Ref.4) and cannot be
reproduced by present LSSM calculations using standard effective charges as well as proton and neutron
excitation across the N = Z = 50 shell.

†Condensed from the article in Phys. Rev. C 90, 061302(R)(2014).
∗1 RIKEN Nishina Center∗2 Research Center for Nuclear Physics, Osaka University∗3 Center for Nuclear Study, University of Tokyo∗4 Department of Physics, Rikkyo University∗5 CEA Saclay∗6 State Key Laboratory of Nuclear Physics and Technology,
Peking University∗7 Niewodniczanski Institute of Nuclear Physics, Polish
Academy of Sciences∗8 National Institute of Technology, Ichinoseki College∗9 Instituto de Estructura de la Materia, CSIC
∗10 Department of Physics, University of Tokyo∗11 Department of Physics, Tokyo University of Science∗12 Institute for Nuclear Research of the Hungarian Academyof Sciences

References
1) A. Banu et al., Phys. Rev. C 72, 061305 (2005).
2) A. Ekström et al., Phys. Rev. Lett. 101, 012502 (2008).
3) C. Vaman et al., Phys. Rev. Lett. 99, 162501 (2007).
4) G. Guastalla et al., Phys. Rev. Lett. 110, 172501 (2013).
5) V. Bader et al., Phys. Rev. C 88, 051301(R) (2013).
6) T. Kubo et al., Prog. Theor. Exp. Phys. 2012, 03C003(2012).
7) S. Takeuchi et al., Nucl. Instr. Meth. A 763, 596 (2014).

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