II-9. Instrumentation

RIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

Silicon trackers for cluster knockout reactions in ONOKORO
K. Higuchi,∗1,∗2 J. Tanaka,∗1 T. Uesaka,∗1 R. Tusuji,∗3 J. Zenihiro,∗1,∗3 S. Kawase,∗4 S. Kurosawa,∗5
S. Takeshige,∗1,∗6 H. Baba,∗1 and Y. Hijikata∗1,∗3 for the ONOKORO Collaboration

Fig. 1. Silicon detectors mounted for the text experiment atthe HIMAC. A silicon wafer with vertical strips is placedin front of that with horizontal strips.
∗1∗2∗3∗4∗5∗6RIKEN Nishina Center
Department of Physics, Toho University
Department of Physics, Kyoto University
Department of Advanced Energy, Kyushu University
Institute for Materials Research, Tohoku University
Department of Physics, Rikkyo University- 75 -count [ - ]In August 2021 at HIMAC, we evaluated the responses of the silicon detectors to proton and α beams.
Four silicon detectors, two each for measuring the positions in the X and Y directions with 100 μm strips,
were installed in the beamline. Figure 2 shows the energy loss spectra of the proton 100 MeV beam and theα particle 230 MeV/nucleon beam in one silicon layer,respectively.
count [ - ]We developed silicon trackers for the cluster knockout
reactions toward the ONOKORO1,2) project at RIKEN,
Nishina Center. Particle tracking with a good position resolution is necessary to measure the angle of theemitted particles from the cluster knockout reactions.
The multi-channel signals from the silicon-strip detectors were pre-ampliﬁed and shaped (50 ns CR-RC circuit) using the ASIC integrated circuits APV25.3) Eachof these ASIC can treat 128 channels. The unit siliconwafers with 7.68 cm width (768 strips) require twelvechips (see Fig. 1), which actually operate 1536 channels. The half (odd) channels were connected to thestrip electrodes of the silicon detector by wire bonding, and the other (even) half were used to measure
the sync common-mode noises and subtract them fromthe odd channels. Skipping channels with no signal reduces the number of readout channel. As it does not
generate a trigger signal by itself, the basic operation
involves synchronizing with external triggers. The output of the shaping circuit was held at the timing ofan external trigger and was converted into a serial signal using an analog multiplexer. The serial signal wasdigitized using an ADC module (ADCM) and the data
was acquired by the DAQ based on the TRB3 (TDCReadout Board V3) system.

600

40040020020000200400(a)600Energy [ keV ]00200400(b)600Energy [ keV ]Fig. 2. Energy loss spectrum of (a) 100 MeV proton beam(b) 230 MeV/nucleon alpha-particle beam.

The distribution of small energy loss is known to bea Landau distribution. In (a) with proton beam, theﬁtting was performed using a Landau function convoluted by a Gaussian. It reproduced the pedestal widths(4.15 keV). In (b), the larger energy loss with the alphaparticle beam provides a rather symmetrical distribution. This result revealed that the responses of the silicon detectors, including the electric circuit, were undercontrol. Moreover, we also evaluated the detection eﬃciencies. The particles were guaranteed to pass throughthe detector by detecting them in the same events inthe front and back. In a low intensity (1 k cps) condition, 91.4% of the events had a single hit, and 8.10%
were double hits. In the double hits, 75.7% were adjacent strips. Events with more than triple hits were0.47%. Consequently, it was found that it is possible touniquely determine the hit position with 97.5% in eachsilicon layer. The high detection eﬃciency under smallenergy loss conditions encouraged us to develop the fullsilicon detector array in the future.
References
1) T. Uesaka et al., Grant-in-Aid for Specially Promoted
Research, Grant Number 21H04975.
2) T. Uesaka et al., RIBF Construction Proposal, “TOGAXSI: a new detector array for inverse-kinematics cluster and nucleon knock-out reaction experiments” (2021).
3) L. Jones, APV25-S1 User Guide V2.2 (2001).

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