Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 47 (2014)

Development of a γ-ray calorimeter for the measurement of highly
excited states
Y. Togano,∗1,∗2 M. Shikata,∗1 Y. Kondo,∗1,∗2 and T. Nakamura∗1,∗2
The γ-ray calorimeter CATANA (CAlorimeter for
γ-ray Transitions in Atomic Nuclei at high isospin
Asymmetry) has been developed to measure highly
excited states such as the pygmy dipole resonanceand/or the giant dipole resonance. CATANA will
be used with the SAMURAI facility at RIBF.1) The
excitation energy spectrum will be reconstructed bycombining the invariant mass of the reaction products measured by SAMURAI and γ-ray energies fromCATANA. CATANA is focused on achieving a highdetection eﬃciency because the probability of multiple
γ-ray emissions is high in the decay of the highly excited states. Our goal is to achieve 55% photo peakeﬃciency for a 1 MeV γ ray from a beam with velocity
β = 0.6.
The cross-sectional view of the CATANA array isshown in Fig.1. The array consists of 200 CsI crystals,
whose thickness ranges from 9 cm to 15 cm. The colors indicate the diﬀerent crystal shapes. The array iscomposed of six crystal shapes to minimize the empty
space between the crystals. The crystals at the forward angle are thicker to cope with the Doppler shiftof the γ energy. The array covers angles from 10◦ to120◦ along the beam axis. The angular coverage perone crystal along the beam axis is about 9 degrees, andperpendicular to the beam axis, it is 18 degrees. The
space inside the array is of ellipsoidal shape, whose major radius is 25 cm and minor radius is 20 cm. R11265(Hamamatsu) PMTs will be used for two types of forward detectors, shown as yellow and saﬀron yellow inFig. 1, and R580 (Hamamatsu) PMTs will be used
for other detector shapes. Signal from a PMT will

be processed in the spectroscopic ampliﬁer 4494 from
Clear Pulse Corporation. The pulse height informationfrom the ampliﬁer is digitized by a Mesytec MADC32
ADC. The timing information is processed in the 4494
ampliﬁer using a build-in constant fraction discriminator, and digitized by a CAEN V1190A TDC. The logic
trigger signal is generated as an “or” signal from thetiming information.
The detection eﬃciency and the energy resolution ofthe CATANA array was estimated by using a MonteCarlo simulation based on the code GEANT4. Thethickness of the crystal housing and the space between
the housing and crystal were assumed to be 1 mm in
the simulation. The eﬃciency was calculated as 56%
and 36% for 1 MeV and 10 MeV γ rays, respectively,from a beam with velocity of β = 0.6.
The prototype CsI crystal was tested at the Tokyo
Institute of Technology. Fig. 2 shows the prototypeCsI(Tl) crystal. The thickness of the crystal is 9 cm,and the shape of the prototype crystal corresponds tothe blue one in Fig.1. The R11265 PMT is attached at
the top side of the crystal. The crystal is wrapped by
the ESR ﬁlm (3M) of 65 µm and Teﬂon tape as reﬂectors. An energy resolution of 8.5% was achieved for the662 keV γ ray with the prototype crystal. Based on themeasured resolution, the energy resolution (FWHM) of
13% and 9% for 1 MeV and 10 MeV γ rays, respectively, from a beam at β = 0.6 is expected with theentire CATANA array.
The fabrication of 200 crystals will commence inspring 2014, and the entire system will be completedby spring 2015.

Fig. 2. Photograph of the prototype CsI(Tl) crystal.
Fig. 1. Cross-sectional view of the CATANA array. Colorsof crystals correspond to their shapes.

References∗11) T. Kobayashi et al.: Nucl. Instr. Meth. B 317, 294(2013).

∗2

Department of Physics, Tokyo Institute of Technology
RIKEN Nishina Center- 179 -