RIKEN Accel. Prog. Rep. 48 (2015)

Ⅰ. HIGHLIGHTS OF THE YEAR

Measurement of isochronism using α-source for the Rare RI Ring
Y. Abe,∗1,∗2 Y. Yamaguchi,∗1 M. Wakasugi,∗1 T. Uesaka,∗1 A. Ozawa,∗2F. Suzaki,∗1,∗3 D. Nagae,∗2 H. Miura,∗3 and T. Yamaguchi∗3Figure 2 shows the results of measurement and simulation by MOCADI.3) To evaluate the optimum gradientvalue, we ﬁtted the results with a parabolic function.
The obtained mean value of 0.207(2) is in very goodagreement with the simulation result of 0.205. Thisshows that our isochronous ﬁeld calculation was correct and an isochronous ﬁeld is formed using trim coils.
The ﬁnal observed width had 0.61 ns standard deviation. However, the width was limited by the timing
resolution of the detectors. Therefore, the achieved
isochronism of the ring was less than 1.3 × 10−4 .
3.5

standard deviation [ns]

The Rare RI Ring was constructed at the RIBF
to measure the masses of nuclei pertinent to the rprocess.1) We performed an oﬄine machine study using
α-source (241 Am). The α-source was placed in the ringon the central orbit at the R-MD1 area after the ﬁrst
sector as shown in Fig. 1. First, we tried transporting the α particle in the ring and succeeded. Next, toconﬁrm the isochronous ﬁeld of the ring, we measured
TOF after one revolution using two detectors. One wasa carbon foil detector like a circulation detector of thisring,2) and the other was a plastic scintillator. The
carbon foil detector consisted of thin carbon foil (60µg/cm2 thickness) and three wired plates. A schematic
view of these detectors is shown in Fig. 1. The carbon
foil detector was placed in front of the source, whereas
the plastic scintillator was placed behind the source todetect the α particle after one revolution. A delayed
signal from the carbon foil detector was used as a stop
signal of TOF, and a signal from the plastic scintillator
was used as a start signal.

Simulation
Measurement

3.0

Fitting

2.5
2.0
1.5

mean = 0.207(2)

1.0
0.5
0.0
0.16

0.17

0.18

0.19

0.20 0.21

0.22

0.23

0.24

0.25

(∂B/∂r)/B0
α-ray
R-MD1(W+Au) wire
(φ 40 µm)

C-foil(60 µg/cm2)

Fig. 2. Results of measurement (closed circles) and comparison with simulation (dashed line). The solid line is
the result of ﬁtting with a parabolic function.

241Am

α-rayeMCP

Plastic
scintillator

Fig. 1. Setup of α-source and detectors. The carbon foil
detector was placed in front of the α-source, whereas
the plastic scintillator was placed behind.

The obtained TOF was 4643.5(6) ns which corresponds to an α particle with 0.87 MeV/nucleon. This
energy is equivalent to the value calculated from energy loss by the cover of the source and the carbon
foil. In addtion we measured TOF while changing theradial gradient of the magnetic ﬁeld using 10 trim coils.
∗1
∗2
∗3

It is seen from our results in Fig. 2 that the standard
deviation was saturated. This saturation was causedby the limitation of timing resolution of the detectors.
Currently, we are testing an injection system to store
the α particle from the source for several revolutions. If
we can measure the TOF after several revolutions, wewould be able to conﬁrm the isochronism with higher
order even though the timing resolution of the detectors is limited. Furthermore we will perform a machine
study using a heavy-ion beam in the next ﬁscal year.
References
1) Y. Yamaguchi et al.: RIKEN Accel. Prog. Rep. 46 xiv(2013)
2) Y. Abe et al.: JPS Conf. Proc. 1, 013059 (2014)3) N. Iwasa et al.: Nucl. Instrum. Methods B 126, 284(1997)RIKEN Nishina Center
Institute of Physics, University of Tsukuba
Department of Physics, Saitama University- 24 -

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