Search

The purpose of this work is to develop a validated Geant4 simulation model of a whole-body prototype PET scanner constructed from the four-layer depth-of-interaction detectors developed at the National Institute of Radiological Sciences, National Institutes for Quantum and Radiological Science and Technology, Japan. The simulation model emulates the behaviour of the unique depth of interaction sensing capability of the scanner without needing to directly simulate optical photon transport in the scintillator and photodetector modules. The model was validated by evaluating and comparing performance metrics from the NEMA NU 2-2012 protocol on both the simulated and physical scanner, including spatial resolution, sensitivity, scatter fraction, noise equivalent count rates and image quality. The results show that the average sensitivities of the scanner in the field-of-view were 5.9 cps kBq−1 and 6.0 cps kBq−1 for experiment and simulation, respectively. The average spatial resolutions measured for point sources placed at several radial offsets were 5.2± 0.7 mm and 5.0± 0.8 mm FWHM for experiment and simulation, respectively. The peak NECR was 22.9 kcps at 7.4 kBq ml−1 for the experiment, while the NECR obtained via simulation was 23.3 kcps at the same activity. The scatter fractions were 44% and 41.3% for the experiment and simulation, respectively. Contrast recovery estimates performed in different regions of a simulated image quality phantom matched the experimental results with an average error of -8.7% and +3.4% for hot and cold lesions, respectively. The results demonstrate that the developed Geant4 model reliably reproduces the key NEMA NU 2-2012 performance metrics evaluated on the prototype PET scanner. A simplified version of the model is included as an advanced example in Geant4 version 10.5. [ABSTRACT FROM AUTHOR]

Scintillation detectors are commonly used as radiation detectors. For the detection of heavy ions a non-linearity in scintillation light output is observed which is known as ionization quenching. In this paper we investigate whether the ionization quenching for BGO scintillators depends on temperature. This would impact the validity of ionization quenching correction models in temperature unstable environments. We measured temperature dependent light output curves for several ion species at different energies at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. We find that the normalized temperature dependent light output curves show the same temperature dependence for all ion species and energies. Therefore, we conclude that the effect of ionization quenching in BGO is independent of temperature. Thus the temperature dependence of scintillation light output and the effect of ionization quenching are independent and can be separately correct by the already developed models for the scintillation light output of BGO. [ABSTRACT FROM AUTHOR]

Purpose: This study is devoted to optimizing and characterizing the response of a multipoint plastic scintillator detector (mPSD) for application to in vivo dosimetry in high dose rate (HDR) brachytherapy. Methods: An exhaustive analysis was carried out in order to obtain an optimized mPSD design that maximizes the scintillation light collection produced by the interaction of ionizing photons. More than 20 prototypes of mPSD were built and tested in order to determine the appropriate order of scintillators relative to the photodetector (distal, center, or proximal) as well as their length as a function of the scintillation light emitted. The available detecting elements are the BCF‐60, BCF‐12, and BCF‐10 scintillators (Saint Gobain Crystals, Hiram, OH, USA), separated from each other by segments of Eska GH‐4001 clear optical fibers (Mitsubishi Rayon Co., Ltd., Tokyo, Japan). The contribution of each scintillator to the total spectrum was determined by irradiations in the low energy range (<120 keV). For the best mPSD design, a numerical optimization was done in order to select the optical components [dichroic mirrors, filters, and photomultipliers tubes (PMTs)] that best match the light emission profile. Calculations were performed taking into account the measured scintillation spectrum and light yield, the manufacturer‐reported transmission and attenuation of the optical components, and the experimentally characterized PMT noise. The optimized dosimetric system was used for HDR brachytherapy measurements. The system was independently controlled from the 192Ir source via LabVIEW and read simultaneously using an NI‐DAQ board. Dose measurements as a function of distance from the source were carried out according to TG‐43U1 recommendations. The system performance was quantified in terms of signal to noise ratio (SNR) and signal to background ratio (SBR). Results: For best overall light‐yield emission, it was determined that BCF‐60 should be placed at the distal position, BCF‐12 in the center, and BCF‐10 at the proximal position with respect to the photodetector. This configuration allowed for optimized light transmission through the collecting fiber and avoided inter‐scintillator excitation and self‐absorption effects. The optimal scintillator length found was of 3, 6, and 7 mm for BCF‐10, BCF‐ 12, and BCF‐60, respectively. The optimized luminescence system allowed for signal deconvolution using a multispectral approach, extracting the dose to each element while taking into account the Cerenkov stem effect. Differences between the mPSD measurements and TG‐43U1 remain below 5% in the range of 0.5 to 6.5 cm from the source. The dosimetric system can properly differentiate the scintillation signal from the background for a wide range of dose rate conditions; the SNR was found to be above 5 for dose rates above 22 mGy/s while the minimum SBR measured was 1.8 at 6 mGy/s. Conclusion: Based on the spectral response at different conditions, an mPSD was constructed and optimized for HDR brachytherapy dosimetry. It is sensitive enough to allow multiple simultaneous measurements over a clinically useful distance range, up to 6.5 cm from the source. This study constitutes a baseline for future applications enabling real‐time dose measurements and source position reporting over a wide range of dose rate conditions. [ABSTRACT FROM AUTHOR]

Boron Neutron Capture Therapy (BNCT) is a promising cancer therapy, which has recently been in practical use in Japan especially using an accelerator. In BNCT real-time measurement of local boron dose is required. In the present study, a novel design of a SPECT system for BNCT (BNCT-SPECT) has been carried out to realize estimation of the local boron dose, i.e., treatment effect of BNCT. Necessary performance which BNCT community requires includes accuracy of 5% and spatial resolution of 5 mm, which are regarded to be difficult to realize. A possible design was investigated to meet the requirements. The design results we achieved are as follows: As for the elemental detection device, GAGG (3.5 × 3.5 × 30 mm3) was selected, and for the collimator, the collimator hole diameter was 3.5 mm, the collimator hole pitch was 4 mm and the collimator length was 26 cm. For the obtained performance with the design, the accuracy was 4.4% and the spatial resolution was 5.1 mm. Currently prior to production of the real system, a prototype of BNCT-SPECT is being developed to acquire real projection data to confirm the performance and examine our own image reconstruction method with the obtained projection data. • Boron Neutron Capture Therapy (BNCT) is a promising radiation therapy for cancer. •A novel SPECT system for BNCT (BNCT-SPECT) is required to monitor local boron dose in real-time. •Design of BNCT-SPECT was completed to meet the requirements of measuring accuracy of 5% and spatial resolution of 5 mm. •The obtained design performance is 4.4% of the accuracy and 5.1 mm of the spatial resolution. [ABSTRACT FROM AUTHOR]

Abstract: We report on the measurements performed with relativistic ions from Be to Fe, at the Fragment Separator (FRS) of the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, to test the performance of charge-sensitive detectors that were designed to separate – via multiple dE/dx measurements – fully stripped nuclei of cosmic origin in the experiment CALET. The latter is a space mission by the Japanese Space Agency (JAXA) scheduled to be launched to the International Space Station (ISS) in 2013. The CALET instrument is managed by an international collaboration and it is scheduled to take data for 5 years on the Exposure Facility (JEM-EF) of the Japanese module KIBO on the ISS. The aim of the test was to accurately measure the response of the scintillator to different nuclear species and parametrize the saturation of the scintillation light in order to assess the impact of this effect on the charge resolution of the instrument. [Copyright &y& Elsevier]

Abstract: Japan Atomic Energy Agency has developed the neutron scintillator jointly with Chichibu Fuji Co., Ltd. In this study, we evaluated the new ZnS(Ag):Al/6Li scintillator developed for neutron imaging. It was confirmed that the brightness increased by about double while maintaining equal performance for the spatial resolution as compared with a conventional scintillator. High frame-rate imaging using a high-speed video camera system and this new scintillator made it possible to image beyond 10000 frames per second while still having enough brightness. This technique allowed us to obtain a high-frame-rate visualization of oil flow in a running car engine. Furthermore, we devised a technique to increase the light intensity of reception for a camera by adding brightness enhancement films on the output surface of the scintillator. It was confirmed that the spatial resolution degraded more than double, but the brightness increased by about three times. [Copyright &y& Elsevier]

Indoor radon and thoron concentrations were dominated with their exhalation rate from building materials. Thus, the evaluation of exhalation rate with highly precise is important. This paper presented a new technique to measure the dependence radon/thoron exhalation rate, from building materials used in Japan, on absolute humidity. The measurement technique consisted of a solid state alpha detector equipped a ventilation-type chamber and humidity control system in a flow through method. The exhalation rate of dried samples (Indian red granite and Japanese gray granite) was measured at various absolute humidity levels in the range of 1-20 g cm. It was found that exhalation rate increased exponential with increasing of absolute humidity for both samples. Furthermore, the dependence of radon emanation coefficient on building material's temperature was also studied using an accumulation chamber equipped with scintillation cell alpha detector. The emanation coefficient of dry sample increased proportionally with increasing the material's temperature with a correlation factor of 0.88. [ABSTRACT FROM AUTHOR]

Abstract: We measured the double differential neutron yield at 0°, 30°, 60° and 90° from 12C5+ induced reactions on thick targets of Ti and Ag at 12 MeV/amu at the Cyclotron at National Institute of Radiological Sciences, Inage, Japan, with 5″ × 5″ proton recoil scintillation detectors BC-501. The measured neutron spectra were unfolded using pulse height unfolding algorithm and energy and angular distribution obtained. Energy distribution of neutron ambient dose equivalent, H*(10) and absorbed dose, D at different angles was determined from double differential neutron spectra using ICRP recommended fluence to dose conversion coefficients. [ABSTRACT FROM AUTHOR]

Abstract: A novel custom-developed scintillator for laser fusion diagnostics is reported. With the aim of diagnosing scattered neutrons from the imploded high-density fusion plasma, a fast response lithium-6 glass scintillator has been developed. Praseodymium, instead of the more widely-used cerium was chosen as the dopant. Sufficiently fast luminescence lifetime for scattered neutron diagnostics (<20ns) was experimentally observed, and the feasibility was successfully shown in laser-fusion experiments at the GEKKO XII facility of the Institute of Laser Engineering, Osaka University. [ABSTRACT FROM AUTHOR]

Abstract: In order to visualize water generated in an operating polymer electrolyte fuel cell (PEFC), a neutron radiography (NR) apparatus, composed of a scintillator, optical mirrors and a CCD camera, was installed at a sample position of the focusing and polarized neutron small-angle scattering (SANS) spectrometer (SANS-J-II) at research reactor JRR-3 at Japan Atomic Energy Agency, Tokai, Japan. By combining SANS and NR, we aim to cover a wide length scale from nanometer to millimeter. The new method succeeded in detecting a spatial distribution of the water generated in individual cell elements; NR detected the water in a gas diffusion layer and a flow field, whereas SANS quantitatively determines the water content in a membrane electrode assembly (MEA). [Copyright &y& Elsevier]

Abstract: We report on the development of a front-end ASIC for high spatial resolution PET detectors with time-of-flight capability based on LYSO scintillator arrays coupled with position-sensitive avalanche photodiode (APD) arrays. The ASIC is designed based on the open-IP LSI project led by JAXA and realized in TSMC CMOS technology. It consists of an 8-channel charge-sensitive amplifier, band-pass filters, differentiators, pulse-height and timing discriminators, and two-channel time-to-amplitude converters. As a result, energy resolution of 9.7% (FWHM) is obtained at 511keV, with a time resolution below 970ps . We will also report on the current status of developing a second-version ASIC designed to have 32-channel analog circuits with improved time resolution. [Copyright &y& Elsevier]

For fine segmented scintillator calorimeter, we need semiconductor-based photon sensor. Progress for MPPC which is developed in Japan is presented. One of the results which is relevant to photon detection efficiency indicates promising future of MPPC. However, further development is required for the dynamic range and operating voltage value. [ABSTRACT FROM AUTHOR]

Abstract: The T2K experiment will study neutrino oscillation properties by directing a high intensity neutrino beam produced at J-PARC in Tokai, Japan, towards the large super-Kamiokande detector located 295km away, in Kamioka, Japan. The experiment includes a sophisticated near detector complex, 280m downstream of the neutrino production target. A key element of the near detectors is the ND280 tracker consisting of two active scintillator-bar target systems surrounded by three large time projection chambers (TPCs) for charged particle tracking. The tracker will provide high statistics samples for studying charged current neutrino interaction rates and kinematics prior to oscillation, so as to better understand backgrounds in the far detector. The tracker is surrounded by the UA1/Nomad dipole magnet and the TPCs will measure the charge, momentum, particle type (through ionization energy loss in the gas) of particles passing through them. Novel features of these TPCs include the rectangular box design, constructed from composite panels, the use of bulk micromegas detectors for gas amplification, electronics readout based on a new ASIC, and a photoelectron calibration system. This paper describes the design and construction of the TPCs, the readout electronics, the gas handling system and shows the performance of a completed TPC as deduced from measurements with particle beams, cosmic rays, and the calibration system. [ABSTRACT FROM AUTHOR]

Abstract: A new photon-counting 2D detector and time-of-flight (TOF) data-acquisition (DAQ) electronics were developed as a system for iBIX diffractometer in J-PARC. The detector system is composed of two ceramic ZnS/10B2O3 scintillator sheets, 256×2 wavelength-shifting (WLS) fibers, eight 64 ch multi-anode photomultipliers (PMT), a high-speed 512-channel amplifier and discriminator, and a 512-channel encoder module with FPGA for time and position determination. The scintillator sheets have high detection efficiency, 30% and 45% at 1.8Å for 0.2 and 0.3mm in thickness, respectively. The WLS fibers (0.5-mm square type) are arranged along X and Y directions with gaps of 0.02mm; therefore the size of one pixel is 0.52mm. The PMT have 17% of quantum efficiency for the light from WLS fibers. The detective region (133×133mm2) has more than 66% in the front face of the detector. The amplifier and discriminator module has 300MHz of frequency band, fixed gain (60), and 20–300mV of discriminator level. The encoder module has many coincidence modes including various pattern-matching methods and a centroid-computation method. The pulse-pair resolution is 4–5μs. For the DAQ module, we can use both of histogram and event modes for measurement. The recording rate is 5×105 events/s for the event mode. Maximum number of the time-channel bins is 4096 for the histogram mode. [Copyright &y& Elsevier]

Reports on the Telescope Array (TA) in Utah that will combine fluorescence and scintillation detection methods to resolve the discrepancy in the observed rates of ultrahigh-energy cosmic rays. Features of the TA fluorescence detectors; Functions of TA; Amount invested by Japan in the research.