Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 49 (2016)

Production of low-energy 4.17 MeV/nucleon 9 C beam withpolyethylene degrader at RIPS
E. Milman,∗1,∗3 T. Teranishi,∗2 S. Sakaguchi,∗1,∗2 K. Abe,∗4 Y. Akiyama,∗1,∗2 D. Beaumel,∗1,∗5S. Chebotaryov,∗1,∗3 T. Fukuta,∗1,∗2 A. Galindo-Uribarri,∗6 S. Hayakawa,∗4 S. Hwang,∗7 Y. Ichikawa,∗1N. Imai,∗4 D. Kahl,∗4 R. Kaku,∗1,∗2 T. Kaneko,∗1,∗8 D. Kim,∗1,∗9 W. Kim,∗3 N. Kitamura,∗4 Y. Norimatsu,∗1,∗2E. Romero-Romero,∗6 D. Sakae,∗1,∗2 Y. Sakaguchi,∗4 M. Sasano,∗1 K. Tateishi,∗1 T. Uesaka,∗1 K. Yamada,∗1,∗8and H. Yamaguchi∗4Theoretically, four low-lying 10 N levels are expected
as broad and overlapping resonances1,2) . The levelstructure of 10 N is very important to understand resonances in 10 Li because 10 N and 10 Li are the mirror
nuclei expected to have a similar structure. The information of 10 Li levels can be used to constrain the9Li+n potential, which is required for constructing thethree-body model of the borromean nucleus 11 Li.
We proposed to measure the excitation function ofthe (differential) cross section and vector analyzing
power (Ay ) for the 9 C+p reaction to determine thesebroad resonances3) . The thick-target method in inverse kinematics4) will be used for the measurement.
In this method, the excitation functions for the crosssection and Ay will be scanned with a single beam energy utilizing the energy loss of the beam particle inthe target. The range of center-of-mass energy is set to
1−5 MeV to cover the theoretically expected groundstate of 10 N and several excited states.
In September 2015, a test 9 C+p resonant scatteringexperiment was conducted at RIPS, where the production of a low-energy 9 C beam was tested and theexcitation function was measured with an unpolarized
polyethylene ((CH2 )n ) target. A 9 C beam was produced using a 70-MeV/nucleon 12 C primary beam withan intensity of 400 particle-nA and a 4-mm Be primarytarget at RIPS. The configuration of RIPS is describedin Ref. [5]. A wedge-type degrader with d/R at 0.8,
where d is the central thickness of the degrader and R
is the range of 9 C with a central momentum, was used
at F1 to degrade the 9 C beam energy. In order to realize a high transmission efficiency of 9 C from F1 to F2, aconventional aluminum F1 degrader was replaced witha new (CH2 )n degrader, because the multiple scattering effect, which is serious at d/R ∼0.8, can be highly
reduced with a low-Z material.
The central thickness of the (CH2 )n degrader was set
to 316 mg/cm2 so that the energy loss of the 9 C beam
was equal to the energy loss in the standard Al de∗1∗2∗3∗4∗5∗6∗7∗8∗9RIKEN Nishina Center
Department of Physics, Kyushu University
Department of Physics, Kyungpook National University
CNS, The University of Tokyo
IPN Orsay
Oak Ridge National Laboratory
JAEA
Department of Physics, Toho University
Department of Physics, Ewha Womans University- 160 -grader with 444 mg/cm2 thickness. The wedge angle ofthe degrader was set to 5 mrad based on the LISE++code6) calculation.The intensity of the 9 C beam wasmeasured at F2 for the two cases using the standard
Al degrader and the (CH2 )n degrader at F1. The latter was 1.8 times higher than the former, which shows
improvement of transmission using the low-Z material
for the F1 degrader.
The 9 C beam energy was determined using the timeof- flight (ToF) measured between a 0.5-mm-thick plastic scintillator installed at F2 and one of two positionsensitive Parallel Plate Avalanche Counters (PPAC)at the F3 focal plane. The energy of the 9 C beam wasprecisely controlled by a rotatable thin polyethylene
degrader installed at the F2 focal plane. The correction for the energy loss in the PPACs was calculated
based on the SRIM code7) . The beam energy determined in this analysis was 4.17 MeV/nucleon with anenergy spread of σ = 0.73 MeV/nucleon.
The identification of the secondary beam particles
was conducted based on the RF and ToF information.
Thus the measured purity and intensity of the 9 C beam
were 15% and 2.4 × 104 pps at F3, respectively. Thesepurity and intensity values are sufficiently high for theplanned resonant scattering experiment.
In conclusion, a 4.17-MeV/nucleon 9 C beam wassuccessfully produced with a thick F1 degrader atRIPS. In the experiment, the transmission of the degraded beam was improved by suppressing multiple
scattering effects in the thick F1 degrader using a lowZ material.
References
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Proc. 1525, 552 (2013).
4) K.P. Artemov et al., Sov. J. Nucl. Phys. 52, 408 (1990).
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6) O. B. Tarasov, D. Bazin, Nucl. Instr. Meth. B 266, 4657
(2008).
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