Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 50 (2017)

Development of energy-control method for slowed-down 93 Zr beam

∗1∗2∗3∗4∗5∗6RIKEN Nishina Center
Department of Physics, Tokyo Institute of Technology
Faculty of Engineering Sciences, Kyushu University
Center for Nuclear Study, University of Tokyo
Department of Physics, Niigata University
Department of Physics, Rikkyo University- 165 -700
without target
after tuning

600
500

without target
before tuning

400
300
with carbon target
after tuning

200
10000102030

40506070
Energy (MeV/u)

Fig. 1. Energy distributions of the 93 Zr beam before (blue)
and after (red) the Bρ tuning of dipoles in the BigRIPS
separator. The goal energy at the center of the carbon
target was 50 MeV/u, and 50.1 MeV/u was achieved.
Counts

The spallation reaction of the long-lived ﬁssion product (LLFP) in nuclear waste might be a key reaction
for nuclear transmutation. The spallation cross sections for the LLFPs were measured on proton anddeuteron targets via the inverse kinematics method
using the RI beam with an energy of 185 MeV/u atRIBF.1) For the cross-section measurement at ∼100
MeV/u,2,3) the aluminum energy degrader was used
to slow down the RI beam. At a lower energy suchas 50 or 20 MeV/u, the inaccuracy of the energy-loss
calculation becomes relatively larger. A new control
method of the RI-beam energy was developed for quick
and precise tuning.
The RI beam of 93 Zr was produced using a 238 U primary beam with 345 MeV/u impinging on a 7-mm Betarget. The aluminum energy degraders were placedat foci F1 and F5, which were the momentum dispersive focal planes of the ﬁrst and second stages of theBigRIPS separator. The thicknesses of the F1 andF5 degraders were 4 mm and 0.5 mm, respectively.
The F1 slit was ±1 mm. A 90-mg/cm2 carbon target
was prepared supposing the spallation-reaction measurement. The goal energy at the center of the carbon
target was 50 MeV/u, and the energy without the carbon target was expected to be 60 MeV/u using theenergy-loss calculation in the target. The energy without the carbon target was measured to be 51.1 MeV/u
by using the time of ﬂight in the ZeroDegree spectrometer, as shown in Fig. 1. The magnetic rigidity
Bρ01 of the ﬁrst dipole was increased by 1.24% basedon the calculated relation between Bρ01 and the energy in the ZeroDegree spectrometer. The magnetic
rigidities of other dipoles were readjusted. The energy
became 60.4 MeV/u, which was almost same as thegoal energy of 60 MeV/u. Hence, Bρ01 was changed
again by −0.37% because the average of the energies
with and without the carbon target, 53 MeV/u, wasslightly large. The ﬁnal energy average, 50.1 MeV/u,
was remarkably close to the goal energy: it was obtained by averaging the peak energies of the two energy
distributions as indicated by the red line in Fig. 1.
For the 20 MeV/u setting, the thickness of the F1degrader was changed to 5 mm. Two energies withand without a CH2 target with a 17-mg/cm2 thickness

CountsT. Sumikama,∗1 D. S. Ahn,∗1 N. Fukuda,∗1 Y. Shimizu,∗1 H. Suzuki,∗1 H. Takeda,∗1 H. Wang,∗1 N. Chiga,∗1H. Otsu,∗1 H. Sakurai,∗1 S. Kawase,∗2 Y. Togano,∗3 A. Saito,∗3 K. Yoshida,∗1 N. Inabe,∗1 S. Kubono,∗1K. Nakano,∗2 J. Suwa,∗2 Y. Watanabe,∗2 S. Takeuchi,∗3 T. Tomai,∗3 A. Hirayama,∗3 M. Matsushita,∗4S. Michimasa,∗4 S. Shimoura,∗4 M. Takechi,∗5 K. Chikaato,∗5 and J. Amano∗6900
800
700600without target
after tuning

without target
before tuningwith CH2 target
after tuningwith CH2 target
before tuning

500
400
300
200
100
00

1020304050
60
70Energy (MeV/u)

Fig. 2. Energy distributions before (blue) and after (red)the Bρ tuning of dipoles for the 20 MeV/u setting of
the 93 Zr beam.

were measured for an initial condition to obtain theaverage, which was 27.0 MeV/u, as shown in Fig. 2.
An average energy of 20.2 MeV/u was successfully obtained after Bρ01 was changed by −0.56%. The energy
after the CH2 target was 16.9 MeV/u and its width
was 0.82 MeV/u (FWHM), which corresponds to 2.4%
(FWHM) in momentum. The position and angle distributions on a secondary target were also optimized
in a later experiment.4)
This work was funded by ImPACT Program ofCouncil for Science, Technology, and Innovation (Cabinet Oﬃce, Government of Japan).
References
1) H. Wang et al., Phys. Lett. B 754, 104 (2016).
2) H. Wang et al., RIKEN Accel. Prog. Rep. 49, 8 (2016).
3) S. Kawase et al., RIKEN Accel. Prog. Rep. 49, 87(2016).
4) T. Sumikama et al., RIKEN Accel. Prog. Rep. 50 (submitted).