Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 49 (2016)

Status of the (p, 2p) silicon tracker for upcoming fission experimentswith the SAMURAI spectrometer
S. Reichert,∗1,∗2 M. Sako,∗2 M. Sasano,∗2 D. Mücher,∗3 H. Baba,∗2 C. Berner,∗1 M. Böhmer,∗1 N. Chiga,∗2R. Gernhäuser,∗1 W. F. Henning,∗4 T. Kobayashi,∗5 Y. Kubota,∗2,∗6 R. Lang,∗1 L. Maier,∗1 V. Panin,∗2L. Stuhl,∗2 E. Takada,∗7 T. Uesaka,∗2 L. Werner, ∗1 and J. Yasuda∗2,∗8∗1∗2∗3∗4∗5∗6∗7∗8Department of Physics, Technical University Munich
RIKEN Nishina Center
Department of Physics, University of Guelph
ANL
Department of Physics, Tohoku University
Center for Nuclear Studies, University of TokyoNIRSKyushu University- 167 -b)# of counts# of counts(pedestal run).

ADC value

For studying the fission induced by the (p, 2p) reaction with RI beams of heavy unstable nuclei1) , a (p, 2p)
setup with high missing mass resolution will be installed2,3) . Therefore a collaboration between RIKEN
and TUM is developing two major new detector components: A time-of-flight (TOF) detector assembly todetermine the energy of light charged particles, and asilicon tracker array presented here. Typical energiesof the detected protons range 80 to 200 MeV, resulting
in a low energy loss of 60 to 150 keV.
The silicon tracker is a two-arm setup with three layers of 100 µm thick, single-sided strip detectors witha pitch of 100 µm3) . The strips of the first two layers are oriented vertically to determine the first-orderpolar angles, while the third layer strips are oriented
horizontally. With an additional beam tracking bydrift chambers in front of the target, we derive highresolution reconstruction for both polar and azimuthal
angles. Results of Geant4 simulations with 3-mm-thick
CH2 show an expected angular resolution of σ ∼ 3mrad.
The silicon wafers were designed by M. Sako andpurchased by RIKEN. They were sent to TUM inNovember 2015. The PCB design and the electronics for readout are from TUM. Preliminary tests of theindividual detector PCBs were conducted in Munich
before the PCBs were subsequently shipped to Japan
where integration into the BABIRL DAQ system wasperformed.
For one detector, maximum trigger rates of 15 kHz in
raw data mode and 50 kHz in zero suppressed, pedestal
corrected mode (normal mode) were achieved. Theserates are currently limited by the data transfer to theBABIRL-DAQ computer and have to be scaled downby the number of detectors for the full setup to 1 kHz.
Using a coincidence trigger signal from beam tracking
detectors and the abovementioned TOF detectors, weexpect only rates below 100 Hz in a typical experimental scenario at HIMAC and RIBF.
The small energy loss in the silicon renders the detector noise level a critical issue. The noise level canbe evaluated in raw data mode with random triggers

Bonded pad ofthe APV with

9450

9500

ADC valuec)

Unbonded padof the APV with

9450

9500

ADC valuea)

APV channels

Fig. 1. Pedestal run of the first layer with 768 strips. Herethey are divided into 12 groups representing the 12
APV25s with 128 channels each (64 bonded).

Figure 1(a) shows the ADC values for all the APVchannels used for the detector in the first layer where
every second channel is bonded. Typical noise levels
for bonded channels are in the range of σ = 10 ADC
units, see Fig. 1(b), while the unbonded, reference
channels in Fig. 1(c) show a more narrow distributionof σ = 5 ADC units. With a calibration of 0.5 to 0.6
keV per ADC unit, we expect a signal to noise ratioof 10:1 in the experiment. Recently performed runsof cosmic ray measurements (energy loss of 35 keV)validate this expectation, and the protons were clear
above the set 5 σ thresholds.
This new setup was tested at the end ofFebruary 2016 at HIMAC with the reactions of16O(p, 2p)15 N and 132 Xe(p, 2p) fission each with E =290 MeV/nucleon and 105 pps in inverse kinematic.
In particular, for the first reaction we will be able todemonstrate the missing mass spectroscopy based on
our setup by reconstructing kinetic curves for the firstexcited state at 6.3 MeV with an uncertainty better
than σ = 1 MeV.
References
1) D. Mücher, M. Sasano et al.: Proposal RIBF NP-PAC12 Fission Barrier Studies of Neutron-Rich Nuclei via
the (p,2p) Reaction (2013).
2) D. Mücher, S. Reichert et al.: RIKEN Accel. Prog. Rep.
48 (2015).
3) S. Reichert, M. Sako et al.: RIKEN Accel. Prog. Rep.
48 (2015).