Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 47 (2014)

Commissioning of a LaBr3 (Ce) array with EURICA at RIBF
Z. Patel,∗1,∗2 F. Browne,∗1,∗3 A. M. Bruce,∗3 N. Chiga,∗4 R. Daido,∗5 S. Nishimura,∗1 Zs. Podolyák,∗2
P. H. Regan,∗2,∗6 O. J. Roberts,∗3 H. Sakurai,∗1 P.-A. Söderström,∗1 T. Sumikama,∗4 and H. Watanabe∗7The LaBr3 (Ce) crystals are ∅ 1.5” x 2”, each coupled to a H10570MOD Hamamatsu PMT. The crystals
have removable 5 mm lead shields to prevent crosstalk
between detectors. The configuration can be seen infigure 1. The plastic scintillators measured 45 mm x150 mm x 2 mm and were placed approximately 3 5 mm from the first and last DSSDs.
The PMTs of the LaBr3 (Ce) detectors have an anode and a dynode output for timing and energy measurements respectively. The energy signal was takenfrom the last dynode of the 8-stage PMT and passed toa CAEN N568B shaping amplifier followed by a CAEN
V785 ADC. The time signal from the anode is passed toan Ortec 935 CFD and then divided between a CAENV775 short-range TDC and a CAEN V1190A longrange TDC. A stop signal from the plastic scintillator
at F11 (∼ 1 m before WAS3ABi) or from WAS3ABI isused for the long-range TDC. The stop signal for theshort-range TDC is taken from the plastic scintillators.

An array of 18 LaBr3 (Ce) detectors were introduced
to complement the HPGe EURICA (Euroball-RIKEN
Cluster Array) detectors for the Spring 2013 campaign
at RIBF. These detectors were supplied by The University of Surrey and The University of Brighton toprovide fast-timing information on the half-lives of excited states within radioactive nuclei1) .
LaBr3 (Ce) crystals are very fast scintillators withhigh effective Z and a fast decay time. This makes
them superior to other detectors for γ-ray decay timemeasurements, as they are able to measure half-lives
with a picosecond-nanosecond range while also possessing good energy resolution2,3) .

Fig. 1.: A schematic of one-half of EURICA with
LaBr3 (Ce) detectors, viewed perpendicular to thebeam line. The remaining unseen detectors are arranged at the bottom of the array.

Fig. 2.: Absolute efficiency of the LaBr3 (Ce) detectors
measured using 152 Eu and 60 Co sources.
The absolute efficiency of the LaBr3 (Ce) array isshown in figure 2. This was measured using 152 Euand 60 Co point sources placed inside the WAS3ABichamber, with the LaBr3 (Ce) detectors positioned onaverage ∼ 10 cm from the silicon strip detectors.
Analysis of data taken by the LaBr3 (Ce) detectors
is in progress: preliminary results from half-life measurements in Zr isotopes can be found in reference 4.

Radioactive isotopes were delivered by BigRIPS tothe experimental area, where they were implanted into
WAS3ABi (Wide Angle Silicon Strip Stopper Arrayfor Beta and ion implantation). The resulting γ rays
following the isotope’s decay were detected by thesurrounding HPGe and LaBr3 (Ce) detectors (Fig. 1).
Two plastic scintillators were added to WAS3ABi (oneupstream and one downstream) to provide a stop signal
for the short-range TDC of the LaBr3 (Ce) detectors,
as the silicon detector’s time resolution is too poor athundreds of nanoseconds.
∗1∗2∗3∗4∗5∗6∗7References
1) O. J. Roberts et al., Nucl. Instr. Methods A 748, 91(2014).
2) P. H. Regan et al., EPJ Web of Conferences 63, 01008(2013).
3) O. J. Roberts et al., EPJ Web of Conferences 63, 01018(2013).
4) F. Browne et al., Measurement of Lifetimes of Excited
States in 102 Zr and 104 Zr in this report.

RIKEN Nishina Center
Department of Physics, The University of Surrey
School of Computing, Engineering and Mathematics, The
University of Brighton
Department of Physics, Tohoku University
Department of Physics, Osaka University
Radioactivity Group, National Physics Laboratory
Department of Physics, Beihang University- 13 -