RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-9. Instrumentation

Slowed-down RI beams of 93 Zr and 107 Pd at 50 MeV/u produced forspallation reaction
∗1
∗1
∗1
∗1
∗1
∗1
T.
D.
N.
Y.
H.
H. Takeda,
Takeda,∗1and K.
K. Yoshida
Yoshida,∗1∗1
T. Sumikama,
Sumikama,∗1
D. S.
S. Ahn,Ahn,∗1
N. Fukuda,
Fukuda,∗1
Y. Shimizu,
Shimizu,∗1
H. Suzuki,
Suzuki,∗1H.
andfor ImPACT-RIBF collaboration∗1

RIKEN Nishina Center- 166 -3 x PPACs
Plastic Sci. (100µm)
2 x PPACs
Plastic Sci. (200µm) Target(cooled H2/D2 gas)

Primary beam 238U (345 MeV/u)
Be Target

2 x PPACs
Plastic Sci. (200µm)

F5F0F9F1F2F4F3F6F7F8F10F112 x PPACs
Plastic Sci. (200µm)
Ionization Chamber

2 x PPACs
Plastic Sci. (200µm)

Degraders

ZeroDegree

BigRIPS

Fig. 1. Conﬁguration of target, degrader, and detectors inthe BigRIPS and ZeroDegree spectrometer.
387
4040
Upstream

Downstream
30
CuJoker slitW
Horizontal slit

102

50

X: 8.6 mm
Y: 6.3 mm(FWHM)

40302010100− 10504030Angle (X): 9.2 mrad
Angle (Y): 13.7 mrad
(FWHM)− 30

10201001− 101− 20− 20− 30− 40− 50−50 −40 −30 −20 −10Angle in Y direction (mrad)Fig. 2. Schematic top view of two sets of slits at F1. The
position and angle were restricted by the narrow slit
widths for both sets of slits. The widths of the upstream and downstream slits were ±2 mm and ±10 mm,respectively.
Y (mm)The spallation-reaction cross sections of long-lived
ﬁssion products (LLFPs) on proton and deuteron weremeasured at ∼100 and 200 MeV/u at RIKEN RIBFto search for a method to transmute LLFPs in nuclear
waste1–3) . In the present study, RI beams of 93 Zr and107
Pd were provided for the measurement at an energyof 50 MeV/u. The control method of the RI beam energy was established in a previous experiment4) . This
report gives an outline of RI beam production and new
developments, and approaches.
Figure 1 shows a schematic view of the experimental
setup. The RI beams of 93 Zr and 107 Pd were producedand separated in the BigRIPS separator using a 238 U
primary beam and a 7-mm Be target. The thicknessof the aluminum degraders at F1 and F5 were 5 mm
and 0.5 mm, respectively. The maximum intensity ofthe primary beam was used to make the emittance of
the RI beams small. Under the standard operation,
the acceptance of the momentum and position distributions can be changed by the slits at the momentum
dispersive and achromatic foci, respectively, but theangle distribution is retained. Two new methods weredeveloped to control the angle distributions in the horizontal (X) and vertical (Y) directions. For the X direction, a narrow second slit (Joker slit) at F1 was used
as shown in Fig. 2. The RI beams with a large angle
were stopped in the Joker slit by the use of narrow slitwidths. For the Y direction, the focus position of Y
at F2 was changed from the F2 slit position. Because
the defocus beam on the slit has a correlation between
the angle and position, RI beams with a large angle
were stopped in the F2 Y slits with a narrow width of±2 mm. The position and distribution for 107 Pd areshown in Fig. 3.
Fragments measured in the ZeroDegree spectrometer are produced not only in a secondary target but
also in the detectors at F7 and F8. Although the contribution from the detectors is subtracted by using thedata without the secondary target, a thinner detector
combination can increase the sensitivity of the measurement. The ionization chamber (140 mg/cm2 ) atF7 for the atomic number Z determination of the RI
beam was removed, because Z was determined fromthe energy loss in the F5 degrader instead5) .
The momentum dispersive mode in the ZeroDegree
spectrometer was used to avoid the charge-state changein F9 detectors that was necessary for the achromaticmode. A wide plastic scintillator and ionization chamber at F11 were developed6) . An analysis of the parti-10−1− 4001020304050X (mm)− 50−50 −40 −30 −20 −1001020304050Angle in X direction (mrad)Fig. 3. Position (left) and angle (right) distributions on thesecondary target at F8 for 107 Pd with 50 MeV/u.

cle identiﬁcation in the ZeroDegree spectrometer is inprogress.
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(2017).
5) S. Ota et al., RIKEN Accel. Prog. Rep. 49, 15 (2016).
6) N. Chiga et al., RIKEN Accel. Prog. Rep. 50 (2017).