Session ED: Instrumentation III

BrilLanCe detector energy resolution characterization at HI$\vec{\gamma}$S

The High Intensity $\gamma$-ray source (HI$\vec{\gamma}$S) produced a variable $\gamma$-ray beam in the energy range of 2.5 to 15.5 MeV with an energy resolution of 50-100 keV. The $\gamma$-ray spectra from several BrilLanCe detectors (manufactured by Saint-Gobain Cermanics and Plastics, Inc.) were collected over this range of energy. The beam energy resolution was monitored throughout the experiment using a High Purity Germanium (HPGe) detector, running in parallel. The energy resolution of the $\gamma$-ray beam was obtained using a Gaussian fit to deconvoluted HPGe data. Gaussian fits to the BrilLanCe detector spectra were then corrected for the beam energy spread to obtain the detector resolution. A 4$^{''}$(diameter)x 6$^{''}$(long) LaCl$_{3}$Ce detector, a 3$^{''}$x 3$^{''}$ LaBr$_{3}$Ce detector and a 2$^{''}$x 2$^{''}$ LaBr$_{3}$Ce detector are characterized in the present study. The energy resolution of each detector will be reported as a function of incident $\gamma$-ray energy from 2.5 to 15.5 MeV, and the response functions will be compared to spectra obtained with HPGe and NaI detectors.   

Development of a Ge detector array for $\gamma$-ray spectroscopy of hypernuclei at J-PARC

At the J-PARC facility, several light hypernuclei will be studied via $\gamma $-ray spectroscopy at the K1.8 beam line as a Day-1 experiment (E13). $\gamma $ rays from the hypernuclei are detected by a new germanium (Ge) detector array, Hyperball-J (HBJ), for an ultra high energy deposit rate. The array consists of 32 coaxial Ge detectors surrounded by newly developed PWO counters for fast background suppression. The simulated absolute photo-peak efficiency of HBJ is 5.8\% for 1-MeV $\gamma $ ray, which allows for $\gamma$-$\gamma$ coincidence in hypernuclear spectroscopy. Firstly, since the beam intensity is higher than the last experiment at KEK, HBJ will be operated with mechanical cooling for radiation-hardness with the crystal cooled down to below 70 K. The Ge sensor-cooler unit has comparable energy resolution with that of the LN$_2$ cooling. Without a dewar, dense placement of detectors has become possible with adjustable geometry. Secondly, PWO counters will be used in place of BGO counters for the first time. Doping and cooling of PWO crystals achieved the comparable performance to BGO counters even at an order of magnitude higher rate. Finally, HBJ control system has also been being developed. All HBJ components will be remotely controlled and monitored. Results of simulation and the current status of the array will be presented.   

Pulse shape analysis for Ge semiconductor Compton camera

The Compton camera has found applications in many fields such as medical imaging, astrophysics, environmental monitoring and nuclear non-proliferation. We are developing a $\gamma $-ray Compton camera for medical use of multiple molecular imaging, which we call GREI (Gamma-Ray Emission Imaging). The GREI system consists of two double-sided orthogonal-strip high-purity germanium semiconductor detectors. Each detector can detect the interaction position and deposited energy of $\gamma $ ray, and $\gamma $-ray source distributions can be visualized based on Compton scattering kinematics. In order to improve the imaging resolution of the GREI, a pulse shape analysis techniques is under development. In general for the segmented semiconductor detector, its output pulses have variety of the shapes depending on the $\gamma $-ray interaction positions. Therefore, by analyzing the pulse shape, interaction position of $\gamma $-ray interaction can be extracted. Especially, analyzing not only pulse shape appearing in $\gamma $-ray hit segment but also transient signals in neighboring segments, 3D interaction position within the electrode can be extracted. We implemented a pulse shape analysis system for GREI and succeeded to extract 3D interaction position in sub-millimeter order. Consequently, imaging resolution is vastly improved.   

New method of digital waveform analysis of signals from segmented Ge detectors

We study digitized waveforms ($f(t_i)$) from a segmented Ge detector in CNS GRAPE [1], by means of $n$-th ``moments'', $\sum_{i} t^n f(t_i) / \sum_i f(t_i)$ . Nine sets of digitized data of the signal from 3 $\times$ 3 cathodes were recorded by using ADC with 105 MHz sampling [2]. The purpose of the present study is deducing essential information from about 1K-byte waveform data with a simple algorithm to determine the interaction position of $\gamma$-ray. The moments from $n=0$ to $3$ are examined. The characteristics of the moments will be discussed as a function of the hit position. In the preliminary analysis, it shows that the root-mean-square ($n$=2) and the skewness ($n$=3) vary in wide ranges with changing the hit position. \\[4pt] [1] S.Shimoura, Nucl. Inst. and Meth. A 525 (2004) 188.\\[0pt] [2] T.Fukuchi et al., CNS Annual Report 2006 (2006) 77.   

Pulse shape discrimination with new single crystal organic scintillators

Pulse shape discrimination in organic single crystal and liquid scintillators provides a means of identifying fission energy neutrons with high specificity. We present the results of a broad survey of over one hundred single crystal organic scintillators produced from low-temperature solution growth technique. Each crystal was evaluated for light yield and pulse shape discrimination performance. The pulse shape dependence on excitations via a Compton electron from a gamma and a recoil proton from a fast neutron was measured using full waveform digitization. Several groups of compounds were compared in relation to molecular and crystallographic structures, crystal perfection, and the effect of impurities. New prospective materials offering neutron/gamma discrimination comparable or superior to stilbene will be presented. We also report on the growth of large single crystal lithium salicylate and other promising Li compounds which have sensitivity to lower energy neutrons via neutron capture on $^{6}Li$ and are separable from other excitations via pulse shape discrimination.   

Neutron Detection Efficiency of The Crystal Ball and TAPS

Photodisintegration of the deuteron - $d(\gamma,p)n$ and $\pi^0$ production off the deuteron - $d(\gamma,p,\pi^0)n$ channels are investigated to measure the neutron detection efficiency of the combined Crystal Ball and Two Arm Photon Spectroscopy,TAPS, detector system currently employed by the A2 collaboration in the Tagged Photon hall at MAMI accelerator in Mainz,Germany. For this purpose, liquid Deuterium target data with 885 and 1557 MeV beam energy will be compared.Preliminary neutron efficiency results are produced.The resulting efficiencies will be compared to results obtained from a Geant 4 simulation of the complete detector setup in order to validate the neutron response provided therein.The ultimate conclusion of this project will be vital for cross section measurement of channels such as double $\pi^0$ and $\pi^0\eta$ production on the neutron.   

Radiation damage study of a Geiger-mode avalanche photo-diode (MPPC) using a pion beam at TRIUMF

Silicon solid state Geiger-mode avalanche photo-diodes (MPPC) are now available from a several manufacturers. They offer several advantages compared to a conventional PMT -- small size, weight, and even cost. However such solid state devices are also much more susceptible to radiation damage. Previous studies of a Hamamatsu S10362 400 pixel detector have shown significant radiation damage after exposure to 100M protons ($\sim$50 MeV). We have studied the signal deterioration and dark current during irradiation by a 130 MeV/c pion beam at TRIUMF. The results for a total exposure of 5000M pions will be presented.   

Solid-State Photomultiplier with Integrated Front End Electronics

The instrumentation cost of physics experiments has been reduced per channel, by the use of solid-state detectors, but these cost-effective techniques have not been translated to scintillation-based detectors. When considering photodetectors, the cost per channel is determined by the use of high-voltage, analog-to-digital converters, BNC cables, and any other ancillary devices. The overhead associated with device operation limits the number of channels for the detector system, while potentially limiting the scope of physics that can be explored. The PRIMEX experiment at JLab, which is being designed to measure the radiative widths of the $\eta $ and $\eta$' pseudo-scalar mesons for a more comprehensive understanding of QCD at low energies, is an example where CMOS solid-state photomultipliers (SSPMs) can be implemented. The ubiquitous nature of CMOS allows for on-chip signal processing to provide front-end electronics within the detector package. We present the results of the device development for the PRIMEX calorimeter, discussing the characteristics of SSPMs, the potential cost savings, and experimental results of on-chip signal processing.   

Solid-State Avalanche Photodetector for Operation at 4 K

Physics experiments that are conducted at low temperatures and within high magnetic fields require improved optical detectors that operate under these conditions to provide the critical data for new discoveries. One experiment that will push the limits of existing photodetectors is the HIFROST target at the HI$\gamma $S facility at TUNL, where a photodetector is required to readout scintillation material with embedded polarized protons. The readout of the scintillation material with a photodetector is used to reject coherent Compton scattering from $^{12}$C in comparison to scattering of free polarized protons. To ensure proper readout of the scintillation material, a photodetector will be operated at 4 K, and to maintain the polarization of the target, the region will be under a 5T magnet field. We have verified an avalanche photodiode structure that can provide a quantum efficiency of $\sim $20{\%} at 5 K for 532-nm optical photons, even with an onset of carrier freeze out. The solid-state device is fabricated using a commercially available CMOS process, providing a low-cost means for fabrication. The electrical and optical properties of the photodetector are presented.   

J-PARC E17 experiment

Precision x-ray spectroscopy of the 3d-2p X-ray of kaonic helium 3 atoms (J-PARC E17) will be performed as one of the Day-1 experiments at the J-PARC, a new proton synchrotron facility in Japan. By using eight Silicon Drift Detectors (SDDs) which has a high energy resolution of 150 eV (FWHM) and a large sensitive area of 100 mm$^2$, the 2p level shift will be measured with precision of a few eV. Experimental apparatus consist of three parts, x-ray detectors, the cryostat and liquid $^3He$ target, and drift chambers. In this talk, an overview of the detectors and the preparation status will be presented.   

Observing coherent neutrino/nuclear scatters with a dual-phase argon detector

Coherent neutrino/nuclear scatters are a prediction of the Standard Model of particle physics, though they have not yet been observed in the laboratory. We are planning an argon-based dual-phase detector to observe these scatters, and our research program involves three detectors: a single-phase detector to study the systematics of the signal volume, a small dual-phase detector to measure the nuclear quenching factor at 8 keVee, and a large dual-phase detector to search for the neutrino interactions themselves. We will present recent results of the systematic effects of the single-phase detector, including a measurement of gas content via electron drift speed. We will also present a progress update on construction of the small dual-phase detector, as well as a possible design for the large dual-phase detector.   

Development of polarized HD target for LEPS experiment (1)

We develop the method to obtain the polarized proton and deuteron target using the cryogenic technique. In 2008, we firstly completed the cryogenic system to polarize proton in the HD sample and produced firstly the polarized HD sample. The HD sample was cooled down to 15 mK in the period of 2 months with a magnetic field of 17 T, and the polarization and the relaxation time for H and D were measured at 300 mK and at 1 T. We measured the first experimental data at various temperatures and magnetic fields. The H polarization degree is 41.4$\pm$ 3.1\%, and the D polarized degree is 13.1$\pm$ 1.9\%. The polarization degrees measured are lower than those expected, but the reason of the low polarization is considered to be due to non-linear relation between the NMR signal height and the polarization degree. The H relaxation time is 2550$\pm$ 380 hours, and the D relaxation time is 1740$\pm$ 170 hours. The relaxation time is found to be acceptable to produce a new polarized HD target for replacement in continuous experiments.   

Development of polarized HD target for LEPS experiment(2)

We develop the polarized HD target in order to perform the ``complete'' experiments with a polarized photon beam and a polarized target. The first goal of the HD target project is a search for a strange quark content in the nucleon via the $\phi$ meson photoproduction reaction. This experiment is scheduled at the LEPS facility of SPring-8 in 2010. At RCNP, we have already succeeded in producing the polarized HD target and measuring the polarization and relaxation time by using NMR method. The measured relaxation time was not long enough. Since the relaxation time of the HD target depends on its purity, we are developing the purification systems for the HD gas. The next step is transport system for the HD target to SPring-8 by keeping the polarization. We are developing transportation cryostats so as not a sizable depolarization of the HD target. Design and development of the polarized HD target will be reported.