Ⅱ-3. Nuclear Data

RIKEN Accel. Prog. Rep. 52 (2019)

Measurement of neutron production
from 7 MeV/nucleon α incidence on a Bi target
K. Sugihara,∗1,∗2 E. Lee,∗1,∗2 N. Shigyo,∗1,∗2 K. Tanaka,∗1 A. Akashio,∗1 and T. Sanami∗1,∗3°

RF signal and the neutron detector. The TDC resolution was about 0.012 ns/ch. The peak at 3650 ch was
the prompt γ-ray from the α incident reactions. Lowenergy neutrons from the preceding beam bunch wereoverlapped in the TOF spectrum. These events wereexcluded because their small signals were lower than thethreshold level of the electronics. The neutron eventswere extracted by using the diﬀerence in the decay partof the signal between neutrons and γ-rays.1)
The measured neutron TTY and the calculation results by INCL2) and JQMD3) models in PHITS4) code
are shown in Fig. 3. The results of INCL show better
agreement with the experimental results than those ofJQMD.
The measured data will be applied to the shielding
design of the new beam line.

Counts1021010500 1000 1500 2000 2500 3000 3500
TDC [ch]Fig. 2. TOF spectrum at 0◦ .

10 610°710 810°910 10°°exp
INCLJQMD

10 5
TTY [n/sr/MeV/source]

RIKEN has a plan of installing a new beam line forproducing 211 At by α particle incidence on a 209 Bi target. It is assumed that an α beam should have an energyof 7.16 MeV/nucleon to reduce undesired byproducts.
Validation of Monte Carlo simulation codes on radiation shielding is required for the design of a beam line.
The neutron energy spectrum of the 209 Bi(α, 2n)211 At
reaction has not been measured. Experimental data ofdouble-diﬀerential neutron thick target yields (TTY) aredesired as a neutron source term in the radiation shielding design. We measured the neutron energy spectra by
the time-of-ﬂight (TOF) method.
The experiment was carried out at the E7B course of
AVF cyclotron. The experimental arrangement is illustrated in Fig. 1.
The 7.16 MeV/nucleon α beam irradiated a 209 Bi target. The repetition rate of the beam was about 16 MHz.
The integrated beam current was obtained from thecounts of a neutron survey meter set near the targetchamber. The thickness of the target was 2 mm, which
was longer than the range of the α particle.
Neutrons from the target were measured with EJ301
liquid organic scintillators that were 2 inch in diameterand thickness. A 2 mm thick plastic scintillator wasset as a veto detector. The neutron kinetic energy wasdetermined by the TOF method in which the start andstop signals came from the neutron scintillator and theRF signal of the AVF cyclotron, respectively. The ﬂight
path lengths from the target to the detectors were from
1 to 1.2 m as shown in Fig. 1. The background neutrons
were estimated from the measurement data with an ironshadow bar of 60 cm thickness between the target andeach neutron detector.
Figure 2 shows the TOF spectrum at 0◦ . The horizontal axis represents the time diﬀerence between the°10 1110 1210 132468 10 12 14
Neutron Energy [MeV]Fig. 3. Neutron TTY and the calculation results by INCL
and JQMD implemented in PHITS.
Fig. 1. Experimental arrangement.
∗1∗2∗3References

RIKEN Nishina Center
Department of Applied Quantum Physics and Nuclear Engineering, Kyushu UniversityKEK- 80 -1) T. Nakamoto et al., J. Nucl. Sci. Technol. 32, 827 (1995).
2) A. Boudard et al., Phys. Rev. C 87, 014606 (2013).
3) K. Niita et al., Phys. Rev. C 52, 2620 (1995).
4) T. Sato et al., J. Nucl. Sci. Technol. 55 (2018).