Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 51 (2018)

Preparation of the VANDLE array for beta decay studies at RIBF
S. Go,∗1 R. Grzywacz,∗2 J. Bundgaard,∗2 J. Heideman,∗2 T. King,∗2 M. Madurga,∗2 M. M. Rajabali,∗3
M. Singh,∗2 and R. Yokoyama∗2 for the VANDLE collaboration
Owing to the recent developments of RIBF beams
to produce neutron-rich nuclei, the frontier of decay
spectroscopy reached nuclei far from stability where
delayed neutron emission dominates beta decay. Theenergy measurements of neutrons provides the betadecay strength distribution above the neutron separation energy. The strength distribution reﬂects thenuclear structure and allows to predict the decay properties of even more exotic nuclei. One of the experimental techniques to determine the energy of delayed
neutrons is the neutron-time-of-ﬂight measurement.
The Versatile Array of Neutron Detectors at Low
Energy (VANDLE)1) has been constructed at the University of Tennessee. We recently reported strong betadelayed neutron emissions in 83,84 Ga decay2) from Holiﬁeld Radioactive Ion Beam Facility at Oak Ridge National Laboratory with the array. Part of the array isrecently being moved to RIKEN RIBF. The modules ofplastic scintillators with dimensions of 3 × 6 × 120 cm3 .
Both sides of the scintillator are made of Eljen EJ2003) or Bicron BC4084) coupled with PMTs and thetime for each left and right signal is averaged to get theposition independent time. The detectors cover about
20% of the solid angle around the decay station witha 1 m TOF base. The use of digital data acquisitionis essential to achieve good timing resolution. Pixie-16
digitizing modules from XIA LLC allow the digitizingof the signals from detectors sampled at 250 MS/s.

Fig. 1. Part of the VANDLE array setup at RIBF B3F.
The delayed neutron will be detected by the array andthe time-of-flight provides neutron energy.
∗1
∗2
∗3

RIKEN Nishina Center
Department of Physics and Astronomy, University of Tennessee
Tennessee Technological University- 151 -During the BRIKEN experiment6) in November 2017,
we tested our data acquisition system, in particular,
we tested the time stamping capability needed for synchronization with BigRIPS.
While the VANLDE array provides good timing resolution for neutron detection, it is also important todevelop an implantation detector to give the starttiming with good timing resolution. We developeda new, fast timing implantation detector that uses
various types of inorganic scintillators and positionsensitive photomultiplier.5) The implantation detector which was developed for the experiment at RIBF
consists of a segmented YSO scintillator coupled withposition-sensitive PMT. The performance of the detector was conﬁrmed during the BRIKEN experiment.7)
Combining the fast-timing implantation detector andthe VANDLE array will provide suﬃcient timing resolution for neutron-time-of ﬂight measurement. The
construction process for the full VANDLE array for experiments will be completed in the beginning of 2018.
References
1) W. A. Peters et al ., Nucl. Instrum. Methods A 836, 122(2016).
2) M. Madurga et al ., Phys. Rev. Lett. 117, 092502 (2016).
3) Eljen Technology, 1300 W. Broadway, Sweetwater, TX
79556, USA, www.eljentechnology.com.
4) Saint-Gobain Crystals and Detectors, Scintillation
Products, 12345 Kinsman Rd., Newbury, OH 44065,
USA, www.crystals.saint-gobain.com.
5) M. Alsudifat et al ., Physics Procedia 66, 445 (2015).
6) K. P. Rykaczewski et al ., in the report.
7) R. Grzywacz et al ., in the report.