Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 49 (2016)

Beta-delayedneutron
neutron measurement
measurement with new
Beta-delayed
new detector
detectorNiGIRINiGIRI
V.H. Phong,＊1,＊2 S. Nishimura,＊1 J. Liu,＊3 T. Lokotko,＊3 Z. Li,＊4 and J. Lee＊3
A new scintillation detector system NiGIRI1) (Neutron, ionand gamma ray identification for Radioactive Isotope beam)
is under development to measure the energies of neutrons fordecay and reaction studies using the time-of-flighttechnique2). The design of the NiGIRI detector is based on anovel plastic scintillation material EJ-299-33, which has asuperior pulse shape discrimination (PSD) capability3). Eachscintillator bar (30x55x127 mm3) is coupled by two PMTs
(Hamamatsu H11265-200 and R8520-20-12) allowing tolocate the interaction position along the scintillator bar fromthe time difference between two PMT signals.
A feasibility study of the NiGIRI has been conducted inconjunction with the newly developed plastic scintillator
strip detector (MaCi) coupled with the multianode PMT(Hamamatsu H8500B) as a start detector. An array of 26
NiGIRI detectors were arranged in a half-barrel
configuration surrounding the start detector and attached intothe EURICA support frame with a flight path ofapproximately 50 cm. The waveform output from eachdetector was recorded by four flash ADC modules (CAENV1730B) with a sampling rate of 2 ns synchronized with theRIBF DAQ and EURICA DAQ by sharing the clock withLUPO modules. A customized DAQ for the flash ADC withthe capability of processing high data throughput has beendeveloped.
Offline digital pulse processing was performed to extract
useful information such as timing and pulse height toreconstruct the implantation and decay position in the startdetector as well as time-of-flight between the start detector
and NiGIRI detectors in the sub-nano second resolution. By
applying a charge integration method with the optimized
parameters, a clear separation between neutrons and gamma
rays was obtained as shown in Fig. 1 while the time-of-fightwas obtained by using the pulse fitting method.
The test experiment has been carried out in the parasitic
mode with the SEASTAR campaign. Figure 1 shows theexperimental setup. The RI beam after reaction target at F8
focal plane and the Zero Degree Spectrometer (ZDS) tuned
for selecting isotopes around 95Kr was implanted into theMaCi detector at the F11 focal plane while beta delayed
neutrons and gamma rays were measured by the NiGIRI and
the EURICA array.
Figure 2 shows the time-of-flight spectrum combining all
NiGIRI detectors with the decay curve reconstructed in theMaCi detector for the beta-correlated gamma and neutron
events identified with NiGIRI detectors. The delayed neutron
events were selected by gating on a 200 ms window after theRI implantation in MaCi. Possible high energy neutrons haveFig.1. A schematic view of the experimental setup employing
the NiGIRI and MaCi detectors (a). 252Cf source test: PSD
versus total integral. PSD cut (black lines) has been applied
to select neutron events (b). The time-of-flight spectrum
from all NiGIRI detectors after applying PSD cut (c) (small
tail prior to gamma ray peak appeared due to backscattering).

Fig.2. Combined neutron time-of-flight spectrum associatedwith the implantation of the RI beam in the MaCi detector.
The inserted figure shows the time correlation between decay
events and implantation events from the MaCi detector.
been detected from this spectrum.
Further analysis with the available spectroscopic
information of delayed gamma rays from EURICA isundergoing. The result from this test experiment is expected
to provide useful information for the upcoming BRIKEN
project to measure the beta-delayed neutron emission
probability.
References

1) H. Masuzwa et al., RIKEN Accel. Prog. Rep. 48 (2016).
2) Matei et al.; Proceedings of Science, PoS (NIC IX), 138 (2008).
3) S. Nyibule et al.; Nucl. Instr. Meth. A 728, 36-39 (2013).

RIKEN Nishina Center
Faculty of Physics, VNU University of Science, Hanoi.
＊3
Department of Physics, The University of Hong Kong
＊4
School of Physics, Peking University＊1＊2- 169 -