Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 50 (2017)

Intermediate-energy Coulomb excitation of 136 Te
∗5∗6
∗2,3
∗2,4V.
S. Chen,∗2,∗4E. Sahin,
Sahin,∗5Y. Shiga,
Shiga,∗6V.Vaquero,Vaquero,∗1∗1A.
A.Jungclaus,
Jungclaus,∗1∗1P.P.Doornenbal,
Doornenbal,∗2∗2K.
K.Wimmer,
Wimmer,∗2,∗3E.
Y.
∗2
∗2,3
∗7
∗2
∗2,∗3
∗7
D. Steppenbeck,
Steppenbeck, R.
R.Taniuchi,
Taniuchi,Z.Y.
D.
Z.Y. Xu,
Xu, and thethe NP1306-RIBF98R1NP1306-RIBF98R1 collaboration
collaboration

Based on the experience from the ﬁrst intermediateenergy Coulomb excitation experiment performed at104 1)
RIKEN with a heavy (A>100)
ion beam,beam,namelynamely104(A>100) ionSnSn,1)a ,similar
experimenta similar
experimentwas
wasrealized
realizedinin 2015
2015 toto study
the nucleus 136 Te. The main objectives have been i)
to determine a reliable value of the reduced transition
probability, B(E2), to the ﬁrst excited 2+ state basedon the measurement of diﬀerential cross sections as afunction of the scattering angle with both gold andcarbon targets, ii) to search for discrete feeding transitions from higher-lying excited states and to study theinﬂuence of the feeding on the γ-ray angular correlation, and ﬁnally to search for a second 2+ state, onewith mixed-symmetry character.
A primary beam of 238 U at 345 MeV/u with an average intensity of 15 pnA bombarded a 4-mm thickberyllium production target located at the F0 focus ofthe BigRIPS fragment separator. The ﬁssion products
around 136 Te were selected and puriﬁed by employing two wedge-shaped aluminium degraders. The secondary beam was identiﬁed event by event using theΔE-TOF-Bρ method, where the energy loss ΔE wasmeasured by an ionization chamber located at the focalplane F7, Bρ was determined from position measurements using PPACs and the TOF was measured withtwo plastic scintillators located at the focal points F3and F72) . After the selection and identiﬁcation, theFig. 1. Doppler-corrected γ-ray spectrum following Coulomb
excitation of 136 Te. The observed line corresponds to+
the 606 keV, 2+
1 → 0gs transition.
∗1∗2∗3∗4∗5∗6∗7Instituto de Estructura de la Materia, CSIC, Madrid
RIKEN Nishina Center
Department of Physics, University of Tokyo
State Key Laboratory of Nuclear Physics and Technology,Peking University
Department of Physics, University of Oslo
Department of Physics, Rikkyo University
Department of Physics, University of Hong Kong

Fig. 2. The experimental diﬀerential cross sections as function of the scattering angle for inelastic excitation of the136
2+Te on a gold (red) and on a carbon (black)1 state intarget.

secondary beams were transported to the focal point
F8 where they impinged on a 950 mg/cm2 gold targetwith energies around 165 MeV/u. To detect the γ radiation emitted in the decay of the excited states, the reaction target was surrounded by the DALI2 spectrometer. The reaction products left the target with energies
around 110 MeV/u and were identiﬁed by the ZeroDegree spectrometer using again the previously described
ΔE-TOF-Bρ method.
The Doppler-corrected γ-ray spectrum, after selection on 136 Te ions in BigRIPS and ZD, is shown inFig. 1. The ﬁt to the experimental spectrum is shownby the thick black line which is composed of a twoexponential function describing the background (bluedotted line) and individual simulated responses (reddashed line). The line visible in the spectrum corre+136
Te.
sponds to the 606 keV, 2+1 → 0gs transition in
The high statistics accumulated in this experiment isneeded to study in detail the systematic uncertainties
inherent in the determination of B(E2) values using
Coulomb excitation at relativistic energies. The diﬀerential cross sections measured for both the gold and thecarbon target are shown in Fig. 2. The latter is usedto determine the nuclear contribution to the cross section measured with the gold target. The data analysis
is ongoing and the results will be presented soon.
References
1) P. Doornenbal et al.: Phys. Rev. C. 90, 061302(R)(2014).
2) N. Fukuda et al.: Nuc. Instrum. Methods Phys. Res.
Sect B 317, 323 (2013).

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