Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 49 (2016)

Development of a slowed-down beam of 82 Ge at RIBF
T. Sumikama,∗1 D. S. Ahn,∗1 N. Fukuda,∗1 N. Inabe,∗1 T. Kubo,∗1 Y. Shimizu,∗1 H. Suzuki,∗1 H. Takeda,∗1N. Aoi,∗2 D. Beaumel,∗3 K. Hasegawa,∗4 E. Ideguchi,∗2 N. Imai,∗5 T. Kobayashi,∗4 M. Matsushita,∗5S. Michimasa,∗5 H. Otsu,∗1 S. Shimoura,∗5 and T. Teranishi∗6
after beam-line detectors at F8 was measured by using the time of ﬂight between F8 and F9, as shown inFig. 3. The 82 Ge beam with the energy of 13 MeV/u atthe central trajectory was successfully produced. Thetransmission eﬃciency from F2 to F8 was 2%. There
was a reduction of 1/10 mainly due to out of focus at
F7.

RI beams with around 15 MeV/u are necessary forthe study of the nuclear shell structure using the nucleon transfer reaction. The RI-beam energy at RIBF
is typically 250 MeV/u after the ﬁrst stage of the BigRIPS1) . The RI beam is slowed down using energy degraders. However, the control of the energy spread andthe beam size becomes diﬃcult due to the increase in
the beam emittance after the use of energy degraders.
Two methods were proposed to eﬃciently produce aslowed-down beam at RIBF. One is the slowed-down
method with the momentum-compression scheme2) ,and the second method is the use of an RF deﬂector,
called OEDO (Optimized Energy Degrading Optics for
RI beams).3) This paper reports on the ﬁrst test experiment to produce a slowed-down beam of 82 Ge with theenergy of 13 MeV/u using the momentum-compressionscheme.
The RI beam of 82 Ge was produced by the projectile fragmentation of the 238 U beam with the energyof 345 MeV/u. The primary target of beryllium witha thickness of 7 mm was used. A wedge degrader wasplaced at the momentum-dispersive focus F1 to purify
the RI beam, as shown in Fig. 1. The thickness for thecentral trajectory was 5 mm. A second wedge-shaped
degrader with a thickness of 2.0 mm was placed at
the momentum-dispersive focus F5. The wedge angle
was designed to compress the momentum spread. Theion-optics mode obtained after using this degrader waschanged to achieve the momentum achromat. The momentum spread of 6% was compressed to 3%, as shownin Fig. 2. Three energy degraders were also placedat the achromatic foci, F2, F3, and F7. The energy

F0Wedge
DegraderF3BigRIPS

F4SecondStage

F6F7F10∗2∗3∗4∗5∗6δ F5F7 (%)

30

025-2

1520

105-4-20δ F3F5 (%)

204Fig. 2. Results of the momentum compression at the second stage of BigRIPS. δF 3F 5 and δF 5F 7 are (p − p0 )/p0before and after using the momentum-compressive degrader, where p is the momentum and p0 is the momentum at the central trajectory.

20E F8F9 (MeV/u)

10F11158610452-2-10δ F5F7 (%)

1230Fig. 3. Energy after all beam-line detectors at F8 as a function of δ57 . The particle with −0.6 < δ57 < 1.5% wastransported to the ZeroDegree spectrometer.

F8ZeroDegree

Fig. 1. Schematic view of the combination of degraders inthe BigRIPS and ZeroDegree separators. The wedgeshaped degrader was placed at the momentum dispersive foci, F1 and F5, of BigRIPS.
∗135-4Degrader (Flat plate)
F940

20-3F5F1F2FirstStage454References
1) T. Kubo et al.: Prog. Theor. Exp. Phys. (2012) 03C003.
2) T. Sumikama et al.: Energy focusing and RI-beam purification using two energy degraders at fragment separator BigRIPS, RNB8 conference, Grand Rapids, Michigan, May 26 − 30, 2009.
3) M. Matsushita et al.: New energy-degrading scheme
for low-energy reaction measurements of rare isotope
beams, EMIS conference, Grand Rapids, Michigan, May
11 − 15, 2015.

RIKEN Nishina Center
RCNP, Osaka University
INPO, CNRS/IN2PS
Department of Physics, Tohoku University
CNS, University of Tokyo
Department of Physics, Kyushu University- 71 -