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In TOF-PET, the method of timestamp calculation is an important factor that affects coincidence resolving time (CRT). In independent readout detectors, for one-to-one coupled detectors, the first hit (FH) timestamp is the optimal one, while in light-sharing detectors, the optimal timestamp must be calculated from multiple timestamps. The method for the latter performs energy-weighted averaging (EWA) using several photosensors with earlier timestamps, but the light distribution varies depending on the detector structure. Here, we developed an exponentiated energy-weighted averaging (EEWA) method for our previously developed light-sharing detector that limits light spreading. The crosshair light-sharing (CLS) PET detector was developed as a TOF-DOI PET detector. It uses fast LGSO crystals with dimensions of 1.45 × 1.45 × 15 mm3 arranged in a 2D crystal array with three layers of enhanced specular reflectors (ESRs) forming a loop structure within a pair of crystals. The 2D crystal array is optically connected to an 8 × 8 MPPC array. The signals of the MPPC array are individually read out and processed by using TOFPET2 ASICs. To effectively utilize multiple timestamps, the EEWA method introduces a power term to the energy, giving priority to timestamps with higher energy. Additionally, we use Lumirror to increase the light collection efficiency and we compared its performance with the ESRs. In the FH method, the CRTs of the ESR and Lumirror arrays were 250 and 232 ps, respectively. In the EWA method, the CRT deteriorated as the number of MPPCs used was increased compared to the FH method. In the EEWA method, by optimizing the number of MPPCs used and the power factor, the CRT was improved to 226 and 221 ps, respectively. In summary, we developed the EEWA method for timestamp estimation and achieved an improvement of up to 24 ps in CRT. [ABSTRACT FROM AUTHOR]

Previously, we had developed a four-layered depth-of-interaction (DOI) PET detector based on the light sharing method. Reflectors, which were inserted in every two lines of crystal segments and shifted differently for each layer, projected 3D crystal positions onto a 2D position histogram without any overlapping after applying the Anger-type calculation. The best crystal separation we ever obtained was for the four-layered 32 × 32 array of LYSO crystals sized at 1.45 × 1.45 × 5 mm3. However, assembling small crystals tended to cost a lot, and fine tuning of the front-end circuit was required to get fine crystal identification. In this paper, therefore, we proposed a more practical four-layered DOI detector. Its key concept was that the crystals in the top layer, which have the highest detection efficiency, are the biggest contributors to the PET spatial resolution. We applied two new ideas: (1) using quarter size crystals only for the first (top) layer and (2) inserting a thin light guide between the first and the second layers of the crystal array. In the developed prototype detector, we used 24 × 24 LYSO crystals of quarter size (1.4 × 1.4 × 5.0 mm3) in the first layer and the other layers were 12 × 12 arrays of crystals of 2.8 × 2.8 × 5.0 mm3. For better crystal identification of small crystals in the first layer, we optimized the optical condition between crystals by using an optical adhesive and air. Also, the thin light guide of 0.5 mm thickness was inserted between the first and the second layers for improvement of crystal identification of the first layer. With the appropriate insertion of the light guide, all crystals of the first layer were identified as well as the crystals in the other layers. Our developed four-layered DOI detector showed good potential for high spatial resolution without a large increase in the number of crystals. [ABSTRACT FROM AUTHOR]

Time-of-flight (TOF) has become a very important technology in PET, as it reduces noise to improve the PET imaging performance significantly. To obtain a high coincidence resolving time (CRT), it is effective to eliminate inter-crystal scattering (ICS). In one-to-one readout detectors, ICS events can be easily eliminated by setting an energy window for each photo sensor. Removal of ICS events improves CRT but greatly reduces sensitivity. In this work, we developed a simultaneous time-skew and time-walk correction method that suppresses the degradation of CRT even when ICS events are used for a whole-body TOF-PET scanner. A TOF detector with one-to-one readout using fast LGSO and multi pixel photo counter (MPPC) was developed to apply the proposed correction method. To maximize the sensitivity, the crystal size was 3.1 × 3.1 × 20 mm 3 and all sides were chemically polished as the surface treatment. The fast LGSO array was optically connected to an 8 × 8 MPPC array so that the crystals and MPPCs were in one-to-one coupling. In the detector calibration, we worked to improve CRT by separating individual crystal clusters into photoelectric absorption and multiple ICSs on a 2D position histogram and performing simultaneous time-skew and time-walk correction. A pair of TOF detectors was assembled and CRT was measured. When ICS events were removed as much as possible, the CRT of 230.4 ps was obtained, but about 80% of the coincidence events were removed as ICS events. On the other hand, with all events including ICS, the CRT was 320.2 ps. Using the proposed correction method, we improved the CRT to 268.5 ps without causing sensitivity loss. [ABSTRACT FROM AUTHOR]

In advanced ion therapy, the 15 O ion beam is a promising candidate to treat hypoxic tumors and simultaneously monitor the delivered dose to a patient using PET imaging. This study aimed at production of an 15 O beam by projectile fragmentation of a stable 16 O beam in an optimal material, followed by in-beam PET imaging using a prototype OpenPET system, which was developed in the authors’ group. The study was carried out in three steps: selection of the optimal target based on the highest production rate of 15 O fragments; experimental production of the beam using the optimal target in the Heavy Ion Medical Accelerator Chiba (HIMAC) secondary beam course; and realization of in-beam PET imaging for the produced beam. The optimal target evaluations were done using the Monte Carlo simulation code PHITS. The fluence and mean energy of the secondary particles were simulated and the optimal target was selected based on the production rate of 15 O fragments. The highest production rate of 15 O was observed for a liquid hydrogen target, 3.27% for a 53 cm thick target from the 16 O beam of 430 MeV/u. Since liquid hydrogen is not practically applicable in the HIMAC secondary beam course a hydrogen-rich polyethylene material, which was the second optimal target from the simulation results, was selected as the experimental target. Three polyethylene targets with thicknesses of 5, 11 or 14 cm were used to produce the 15 O beam without any degrader in the beam course. The highest production rate was measured as around 0.87% for the 11 cm thick polyethylene target from the 16 O beam of 430 MeV/u when the angular acceptance and momentum acceptance were set at ±13 mrad and ±2.5%, respectively. The purity of the produced beam for the three targets were around 75%, insufficient for clinical application, but it was increased to 97% by inserting a wedge shape aluminum degrader with a thickness of 1.76 cm into the beam course and that is sufficiently high. In-beam PET imaging was also performed for all produced beams using the OpenPET system. The purity improvement of the produced 15 O beams was confirmed from the PET images. [ABSTRACT FROM AUTHOR]

A new scanning system named “Vertex picker” has been developed to rapid collect alpha decay events, which are calibration sources for the range-energy relation in nuclear emulsion. A computer-controlled optical microscope scans emulsion layers exhaustively, and a high-speed and high-resolution camera takes their micrographs. A dedicated image processing picks out vertex-like shapes. Practical operations of alpha decay search were demonstrated by emulsion sheets of the KEK-PS E373 experiment. Alpha decays of nearly 28 events were detected in eye-check work on a PC monitor per hour. This yield is nearly 20 times more effective than that by the conventional eye-scan method. The speed and quality is acceptable for the coming new experiment, J-PARC E07. [ABSTRACT FROM AUTHOR]

We develop a method to diagnose two-dimensional distribution of positron-emitting radioactivity in a rotating object through γ-ray coincidence measurements with two detectors. The principle of this method is same as PET but the measurement system is much simpler. We have constructed a prototype and performed tests with point-like and plate-shaped radioactive sources. The image reconstruction with ML-EM algorithm reproduced the distribution. It can be useful for radiotracer measurements of slow transport processes of materials in a closed system and can find applications in mechanical engineering. [ABSTRACT FROM AUTHOR]

Abstract: One of the challenging applications of PET is implementing it for in-beam PET, which is an in situ monitoring method for charged particle therapy. For this purpose, we have previously proposed an open-type PET scanner, OpenPET. The original OpenPET had a physically opened field-of-view (FOV) between two detector rings through which irradiation beams pass. This dual-ring OpenPET (DROP) had a wide axial FOV including the gap. This geometry was not necessarily the most efficient for application to in-beam PET in which only a limited FOV around the irradiation field is required. Therefore, we have proposed a new single-ring OpenPET (SROP) geometry which can provide an accessible and observable open space with higher sensitivity and a reduced number of detectors than the DROP. The proposed geometry was a cylinder shape with its ends cut at a slant, in which the shape of each cut end became an ellipse. In this work, we developed and evaluated a small prototype of the SROP geometry for proof-of-concept. The SROP prototype was designed with 2 ellipse-shaped detector rings of 16 depth-of-interaction (DOI) detectors each. The DOI detectors consisted of 1024 GSOZ scintillator crystals which were arranged in 4 layers of 16×16 arrays, coupled to a 64-channel FP-PMT. Each ellipse-shaped detector ring had a major axis of 281.6mm and a minor axis of 207.5mm. For the slant mode, the rings were placed at a 45-deg slant from the axial direction and for the non-slant mode (used as a reference) they were at 90deg from the axial direction with no gap. The system sensitivity measured from a 22Na point source was 5.0% for the slant mode. The average spatial resolutions of major and minor axis directions were calculated as 3.8mm FWHM and 4.9mm FWHM, respectively for the slant mode. This difference resulted from the ellipsoidal ring geometry and the spatial resolution of the minor axis direction degraded by the parallax error. Comparison between the slant mode and the non-slant mode showed no remarkable difference in terms of the sensitivity distribution and spatial resolution performance. Therefore, we concluded that the SROP geometry has a good potential as an open geometry especially suitable for in-beam imaging. [Copyright &y& Elsevier]

The X'tal cube is a depth-of-interaction (DOI)-PET detector which is aimed at obtaining isotropic resolution by effective readout of scintillation photons from six sides of the crystal block. The X'tal cube is composed of a 3D crystal block with isotropic segments. Each face of the 3D crystal block is covered with a 4×4 array of multi-pixel photon counters (MPPCs). Previously, in order to fabricate the 3D crystal block efficiently and precisely, we applied a sub-surface laser engraving technique to a monolithic crystal block instead of gluing segmented small crystals. A dense arrangement of multiple micro-cracks carved by the laser beam works efficiently as a scattering wall for the scintillation photons. The X'tal cube with the laser-processed block showed excellent performance with respect to crystal identification and energy resolution. In this work, for characteristics comparison between the laser-processed block and the conventional segmented array block, we made the laser-processed block and two types of segmented array blocks, one with air gaps and the other with glued segmented small crystals. All crystal blocks had 3D grids of 2mm pitch. The 4×4 MPPC arrays were optically coupled to each surface of the crystal block. When performance was evaluated using a uniform irradiation of 511keV, we found that the X'tal cubes with the laser-processed block could easily achieve 2mm3 uniform crystal identification. Also, the average energy resolution of each 3D grid was 11.1±0.7%. On the other hand, the glued segmented array block had a pinched distribution and crystals could not be separated clearly. The segmented array block with air gaps had satisfactory crystal identification performance; however, the laser-processed block had higher crystal identification performance. Also, the energy resolution of the laser-processed block was better than for the segmented array blocks. In summary, we found the laser-processed X'tal cube had excellent crystal identification performance and high energy performance due to its effective dense arrangement of micro-cracks. [ABSTRACT FROM AUTHOR]

Recently, silicon photomultipliers (SiPMs) have become established as photo-sensors for PET scanners. Commercially available SiPM arrays are typically about 3–4 cm in size. In order to develop larger detectors with an Anger calculation, multiple SiPM arrays need to be combined. This configuration requires the use of a light guide and has inactive areas between SiPM arrays. If not addressed, crystal identification degrades not only for peripheral crystals but also for crystals to bridge the gap between the SiPM arrays. On the other hand, we have developed the crosshair light-sharing (CLS) PET detector, which is based on a single-ended readout scheme with roughly quadrisected crystals comparable in size to a SiPM, with depth-of-interaction (DOI) capability. The CLS PET detector based on the local centroid calculation was expected to mitigate the edge effect similar to what the one-to-one coupling detector is able to do. In this work, we developed the axially long CLS PET detector with two multipixel photon counter (MPPC) arrays. The proposed long CLS PET detector consisted of 30 × 14 gadolinium fine aluminum garnet (GFAG) arrays coupled to two 8 × 8 MPPC arrays without the light guide. From 511-keV uniform irradiation, responses of all crystal elements could be separated clearly on a 2D position histogram after applying the Anger calculation. Pulse heights of additional crystals to bridge the gap were 18% lower than those of crystals at the center of the MPPC array, but similar to that of the peripheral crystals based on non-uniformity of the MPPC array. On the other hand, energy resolutions of additional crystals to bridge the gap were almost the same to those of other crystals. The long CLS PET detector promises improvement of the packing fraction while keeping performance. [ABSTRACT FROM AUTHOR]

Abstract: Using present pulsed microwave amplifier, we can obtain RF peak power beyond one hundred MW. However, it is not easy to test such a high-power RF. To overcome this difficulty we developed a high-power microwave attenuator employing a slow wave structure. For example, the output power of RF pulse compressor for present electron linear accelerator reaches a few hundreds MW RF power, but the existing dummy loads can absorb only a few tens MW of RF power. The attenuator we developed has a kind of periodic structure and is made of metal only. We operated this attenuator using a high-power RF source, and found that it could be operated fewer than 50pps RF output at 40MW, or 100MW, . [Copyright &y& Elsevier]

Abstract: Computed radiography (CR) plates made of europium-doped Ba(Sr)FBr(I) were simultaneously exposed to filtered ultraviolet light and visible light in order to erase ghost images, i.e., latent image that is unerasable with visible light (LIunVL) and reappearing one, which are particularly observed in plates irradiated with a high dose and/or cumulatively over-irradiated. CR samples showing LIunVLs were prepared by irradiating three different types of CR plates (Agfa ADC MD10, Kodak Directview Mammo EHRM2, and Fuji ST-VI) with 50kV X-ray beams in the dose range 8.1mGy—8.0Gy. After the sixth round of simultaneous 6h exposures to filtered ultraviolet light and visible light, all the LIunVLs in the three types of CR plates were erased to the same level as in an unirradiated plate and no latent images reappeared after storage at 0°C for 14 days. With conventional exposure to visible light, LIunVLs consistently remained in all types of CR plates irradiated with higher doses of X-rays and latent images reappeared in the Agfa M10 plates after storage at 0°C. Electrons trapped in deep centers cause LIunVLs and they can be erased by simultaneous exposures to filtered ultraviolet light and visible light. To study electrons in deep centers, the absorption spectra were examined in all types of irradiated CR plates by using polychromatic ultraviolet light from a deep-ultraviolet lamp. It was found that deep centers showed a dominant peak in the absorption spectra at around 324nm for the Agfa M10 and Kodak EHRM2 plates, and at around 320nm for the Fuji ST-VI plate, in each case followed by a few small peaks. The peak heights were dose-dependent for all types of CR samples, suggesting that the number of electrons trapped in deep centers increases with the irradiation dose. [Copyright &y& Elsevier]

Abstract: Since 2007, a water-cooled high-power rotating disk target has been in operation at the in-flight radioactive-isotope beam separator (BigRIPS), RIKEN. The target should withstand a goal beam intensity of 1 particle μA (pμA) 238U-beam at 350AMeV with a spot size of 1mm in diameter, resulting in a heat deposit of 22kW in the target. A beam-spot temperature monitoring system using infrared devices in high-radiation environment was elaborately developed. The beam-spot temperature on a beryllium (Be) fixed target and on a rotating Be and tungsten (W) disk target was measured with the most intense beams presently available at our facility. The heat deposit achieved was 0.6kW, that is 1/37 of the goal value. At the present beam intensity, the result supports our estimation that a water-cooled rotating disk target of 30cm diameter can withstand an approximately tenfold beam intensity compared to a water-cooled fixed target. [Copyright &y& Elsevier]

Abstract: The light output responses for protons and carbon nuclei in the KamLAND liquid scintillator were precisely measured using a monochromatic neutron beam. The observed response for proton recoils is well described by Birks formula with the higher-order correction, for the recoil energy from 424keV to 10.5MeV. The response for carbon recoils is also well described by modifying the Birks formula with the nuclear energy loss terms, for the measured recoil energy from 171keV to 2.2MeV. The obtained light output responses were used to estimate the background energy spectrum of the reaction in the KamLAND. The systematic uncertainty of the energy scale in the expected background spectrum was further improved with the measured light output responses. [ABSTRACT FROM AUTHOR]

Abstract: A conventional PET scanner has a 15–25cm axial field-of-view (FOV) and images a whole body using about six bed positions. An OpenPET geometry can extend the axial FOV with a limited number of detectors. The entire whole-body PET scanner must be able to process a large amount of data effectively. In this work, we study feasibility of the fully 3D entire whole-body PET scanner using the GATE simulation. The OpenPET has 12 block detector rings with the ring diameter of 840mm and each block detector ring consists of 48 depth-of-interaction (DOI) detectors. The OpenPET has the axial length of 895.95mm with five parts of 58.95mm open gaps. The OpenPET has higher single data loss than a conventional PET scanner at grouping circuits. NECR of the OpenPET decreases by single data loss. But single data loss is mitigated by separating the axially arranged detector into two parts. Also, multiple coincidences are found to be important for the entire whole-body PET scanner. The entire whole-body PET scanner with the OpenPET geometry promises to provide a large axial FOV with the open space and to have sufficient performance values. But single data loss at the grouping circuits and multiple coincidences are limited to the peak noise equivalent count rate (NECR) for the entire whole-body PET scanner. [ABSTRACT FROM AUTHOR]

Abstract: The temperature dependence of light yield and decay constants of a cerium-doped yttrium aluminum perovskite [YAP(Ce)] scintillator excited by -ray irradiation is studied between 290 and 460K. The scintillation is found to be composed of three decay components with different temperature dependencies. A fast scintillation component with a decay time of is almost independent of temperature; the decay time of the main component decreases from 32 to 26ns with increase in temperature from 290 to 400K but increases above 400K, and a slow component with a decay time larger than 240ns becomes clearly visible at temperatures below 360K. The total light yield increases slightly as the temperature increases up to 330K and decreases above 330K. These results are essentially interpreted using a two-shallow-trap model proposed by Wojtowicz et al., but an additional mechanism would be required at higher temperatures. [Copyright &y& Elsevier]

Abstract: CANDLES is a project to search for neutrinoless double beta decay of 48Ca with scintillators. An effective active shield is achieved by placing the crystals in a liquid scintillator. Energy resolution is improved by converting the ultra-violet light of the scintillator into the visible region with a wavelength shifter dissolved in the liquid scintillator. The newly developed technique, “two phase system of liquid scintillator”, is presented. It will be used to exploit the unique features of the CANDLES system. Experiments to determine liquid scintillator composition will be described. Performance of CANDLES will be demonstrated with prototype detectors. Obtained results indicate that the proposed two phase technique is effective for CANDLES system which will utilize several tons of scintillators. [Copyright &y& Elsevier]

Abstract: A water-cooled high-power rotating disk target is employed at the in-flight radioactive-isotope (RI) beam separator (BigRIPS), RIKEN. For a 238U primary beam with energy of 350AMeV and an intensity of 1 particle μA bombarding a beryllium or carbon target disk with a 1g/cm2 thickness, a total heat loss of 28GW/m2 on the target surface is estimated for a beam-spot size of 1mm in diameter. For the development of a suitable target assembly, a test bench was constructed and has been used for the present RI beam separator (RIPS). A beam spot temperature monitor using an infrared thermo-viewer with telescope lens was developed. The measured temperature for some high-power beam experiments corresponded to results of computer simulations. A radiation hardness test of the magnetic fluid used for a vacuum-tight rotating actuator was performed by irradiating with intense γ-ray converted from an electron beam. No significant change of viscosity was observed up to the total dose of 0.7–1.8MGy. Based on these studies, a practical target system for the BigRIPS separator was designed. To facilitate the maintenance of the target system in a high-radiation environment, a remote-handling maintenance cart system is considered. [Copyright &y& Elsevier]

Abstract: Bi films that we fabricated with vacuum-evaporation deposition show a crystal structure very similar to that of bulk Bi. However they have granular structure on sub-micron scales, and the electrical resistance increases at low temperatures, which is opposite to bulk Bi. A TES microcalorimeter with a Bi absorber shows an energy resolution significantly degraded compared to the baseline resolution. A thermal model of the calorimeter based on the present experimental results indicates that a position dependence of the pulse height and rise time degrades the energy resolution. The position dependence is further considered to be due to mismatch between the rise time of pulse which is mostly determined by the thermal conductance between Bi and TES and the thermal diffusion time in the Bi absorber. [Copyright &y& Elsevier]

Abstract: A depth of interaction (DOI) detector is being developed for the brain PET scanner, jPET-D4. We introduce a light output correction procedure to compensate for variations among the crystal elements in the DOI detector. Under uniform irradiation with 511keV gamma rays, we estimate the light output of each crystal element by identifying each crystal element, and generate a look-up table (LUT) for light output correction. We evaluate the energy resolution of all crystal elements. The energy resolution of 16% is achieved after light output correction for all crystal elements. The DOI detector can correct light output variations that are related to the DOI. We analyze the crystal position dependence of the energy spectra due to inter-crystal scattering among the multiple crystal elements in the DOI detector. It is highly possible that gamma rays interacting with central crystal elements in the crystal array are absorbed by surrounding crystal elements and the Compton part of the energy spectrum is decreased. Inter-crystal scattering has less impact on the energy resolution of the DOI detector. [Copyright &y& Elsevier]

Abstract: Since diagnostic X-rays have been proven to be a cause of cancer, some precautions are essential to reduce the dose delivered to patients. In this paper, an idea to reduce the dose by a new type of X-ray computed tomography (CT) using silicon strip detectors is discussed. Thin tungsten plates placed between edge-on silicon strip detectors are the key element to reduce the background of scattered X-rays and improve the image contrast with low dose. The initial results of a feasibility study are also reported. [Copyright &y& Elsevier]

Abstract: We have designed and developed the flight model silicon micro-strip detector (FM-SSD) for Large Area Space Telescope (GLAST). The concepts and details of the sensor design are described and the results of production testing of the SSDs are reported. A total of 11,500 FM-SSDs were produced in the 2-yr time span from the start of 2001 to the end of 2003. The fabrication was done on the 6-in process line at Hamamatsu Photonics Company. The properties of each SSD were determined by measuring a set of specific parameters. The leakage current and dead channel rate establish a new performance standard for SSD mass production, indicating that the SSD design and fabrication technologies have been well optimized and are well matured. [Copyright &y& Elsevier]

We have evaluated the performance of a prototype 16-channel avalanche photodiode (APD) array developed primarily for scintillating-fiber (SCIFI) tracking detectors. The APD array was coupled to a 2.5m long SCIFI array, and the detection efficiency was measured for minimum ionizing particles passing through the SCIFI array. The APD array was cooled to °C to improve the ratio. We have found that the APD array can read out each individual SCIFI with sufficiently high efficiency. [Copyright &y& Elsevier]

Two kinds of rotating wheel targets for high-power heavy ion reaction have been developed. One is a thick disk target with water-cooling being developed for the in-flight RI beam separator (BigRIPS). An in-beam test was performed using 40Ar beam at 24 AMeV, 1.9 particle μA, with the beam spot size 3 mm in diameter, resulting 0.25 GW/m2 beam power stopped at the surface of carbon disk 2 mm in thickness and 260 mm in diameter. It performed stably without melting. A simulation study has been developed and its possibility for the use of BigRIPS is discussed. The second is a thin target foil mounted on a wheel disk which rotates in He cooling gas of 13.32–133.2 Pa. Its main use is in fusion reactions to search for super-heavy elements by using the gas-filled recoil separator (GARIS). A typical foil is Pb or Bi of 200–300 μg/cm2 in thickness evaporated onto a carbon backing foil of 30 μg/cm2 thickness, and covered by evaporated carbon of 10 μg/cm2 thickness. It can withstand long use under high-intensity 64Ni beam at 311 MeV, and 0.5 particle μA. [Copyright &y& Elsevier]

We introduce two methods to reduce the surface radiation damage of silicon strip detectors. The microscopic reason of surface radiation damage is mainly due to the generation of radiation induced interface traps. The interface traps formation occurs as a result of a series of processes initiated by the creation of electron–hole pairs in SiO2 layer and the subsequent transport of the holes to the SiO2/Si interface. To prevent the transport of holes to the SiO2/Si interface, we tried two different methods. The leakage current after irradiation decreased by 26% and 67% using these methods. [Copyright &y& Elsevier]

The first experimental demonstration of simultaneous measurements of temporally and spatially resolved ion-confining potentials φc and end-loss-ion fluxes IELA has been carried out during a single plasma discharge alone by the use of newly designed ion-energy-spectrometer arrays installed in both end regions of the GAMMA 10 tandem mirror. This position-sensitive ion-detector structure is proposed to obtain precise ion-energy spectra without any perturbations from simultaneously incident energetic electrons into the arrays. The relation between φc and IELA is physically interpreted in terms of Pastukhov’s potential confinement theory. In particular, the importance of axisymmetric φc formation is found for the plasma confinement. [Copyright &y& Elsevier]

The analysis of gamma-ray spectra to identify lines and their intensities usually requires expert knowledge and time-consuming calculations with complex fitting functions. A neural network algorithm can be applied to a gamma-ray spectral analysis owing to its excellent pattern recognition characteristics. However, a gamma-ray spectrum typically having 4096 channels is too large as a typical input data size for a neural network. We show that by applying a suitable peak search procedure, gamma-ray data can be reduced to peak energy data, which can be easily managed as input by neural networks. The method was applied to the analysis of gamma-ray spectra composed of mixed radioisotopes and the spectra of uranium ores. Radioisotope identification was successfully achieved. [Copyright &y& Elsevier]

Alpha-decay events in a nuclear emulsion are standard calibration sources for the relation between the track length and the kinetic energy in each emulsion sheet. We developed an efficient classifier that sorts such alpha-decay events from various vertex-like objects in an emulsion using a convolutional neural network (CNN). We trained the CNN using 15885 images of vertex-like objects, including 906 alpha-decay events, and tested it using a dataset of 46948 images including 255 alpha-decay events. The precision and recall scores of the classification using the previous method without a CNN for the same dataset were 0.081 ± 0.006 and 0.788 ± 0.056, respectively. In contrast, our trained models achieved an average precision score of 0.760 ± 0.006 for the test dataset, after extensively tuning the hyperparameters of the CNN. Moreover, for the model obtained, the discrimination threshold of the classification can be adjusted arbitrarily according to the trade-off between the precision and recall scores. Furthermore, the developed classifier obtained a precision of 0.571 ± 0.017 when the recall score was assigned a value of 0.788. Finally, the developed CNN method reduced the need for additional human visual inspection, required after classification, by a factor of approximately 1/7, compared to the former method without a CNN, proving the feasibility of the proposed classifier. [ABSTRACT FROM AUTHOR]

Abstract: Conventionally, positron emission tomograph (PET) scanners use scintillators which have a high effective atomic number. Recently, novel scintillators like LaBr3 have been developed which have excellent timing and energy resolutions. LaBr3 has a high performance for PET scanner use, but its effective atomic number is lower than that of lutetium oxyorthosilicate (LSO). As an alternative, we have developed a scatter reduction method using depth-of-interaction (DOI) information and energy information to increase the sensitivity. The sensitivity of the PET scanner with LaBr3 can be improved using the DOI-dependent extended-energy window (DEEW) method. In this work, our method is applied to the whole-body LSO/LaBr3 PET scanner using the GATE simulation toolkit. Simulation results show the number of true coincidences can be increased while minimizing the scatter and random coincidences by using the DEEW method. Noise equivalent count rate (NECR) can be improved by 20–70% for the whole-body DOI-PET scanner. Sensitivity of the PET scanner with a scintillator of low-effective atomic number can be improved by the DEEW method. [Copyright &y& Elsevier]

We have developed a four-layer depth of interaction (DOI) detector with single-side photon readout, in which segmented crystals with the patterned reflector insertion are separately identified by the Anger-type calculation. Optical conditions between segmented crystals, where there is no reflector, affect crystal identification ability. Our objective of this work was to improve crystal identification performance of the four-layer DOI detector that uses crystals segmented with a recently developed laser processing technique to include laser processed boundaries (LPBs). The detector consisted of 2 × 2 × 4 mm 3 LYSO crystals and a 4 × 4 array multianode photomultiplier tube (PMT) with 4.5 mm anode pitch. The 2D position map of the detector was calculated by the Anger calculation method. At first, influence of optical condition on crystal identification was evaluated for a one-layer detector consisting of a 2 × 2 crystal array with three different optical conditions between the crystals: crystals stuck together using room temperature vulcanized (RTV) rubber, crystals with air coupling and segmented crystals with LPBs. The crystal array with LPBs gave the shortest distance between crystal responses in the 2D position map compared with the crystal array coupled with RTV rubber or air due to the great amount of cross-talk between segmented crystals with LPBs. These results were used to find optical conditions offering the optimum distance between crystal responses in the 2D position map for the four-layer DOI detector. Crystal identification performance for the four-layer DOI detector consisting of an 8 × 8 array of crystals segmented with LPBs was examined and it was not acceptable for the crystals in the first layer. The crystal identification was improved for the first layer by changing the optical conditions between all 2 × 2 crystal arrays of the first layer to RTV coupling. More improvement was observed by combining different optical conditions between all crystals of the first layer and some crystals of the second and the third layers of the segmented array. [ABSTRACT FROM AUTHOR]

High sensitivity and high spatial resolution dedicated brain PET scanners are in high demand for early diagnosis of neurodegenerative diseases and studies of brain functions. To meet the demand, we have proposed the helmet-chin PET geometry which has a helmet detector and a chin detector. Our first prototype scanner used 54 4-layer depth-of-interaction (DOI) detectors. The helmet detector of the scanner had three detector rings with different radii arranged on a surface of a hemisphere (with a radius of 126.5 mm) and a top cover detector. Therefore, in this study, for our next development, we propose a spherical arrangement, in which the central axis of each detector points toward the center of the hemisphere, and we optimize the size of the detector crystal block to be arranged on the helmet detector. We simulate the spherical arrangement with the optimized crystal block size and compare its imaging performance with the multi-ring arrangement, which has a similar detector arrangement to that of our first prototype. We conduct Monte Carlo simulation to model the scanners having the 4-layer DOI detectors which consist of LYSO crystals. A dead space of 2 mm is assumed on each side of the crystal blocks such as for wrapping. The size of the crystal block is varied from 4×4 mm 2 to 54×54 mm 2 while fixing the thickness of the crystal block to 20 mm. We find that the crystal block sized at 42×42 mm 2 has the highest sensitivity for a hemispherical phantom. The comparison of the two arrangements with the optimized crystal blocks show that, for the same number of crystal blocks, the spherical arrangement has 17% higher sensitivity for the hemispherical phantom than the multi-ring arrangement. We conclude that the helmet-chin PET with the spherical arrangement constructed from the crystal block sized at 42×42×20 mm 3 has better imaging performance especially at the upper part of the brain compared to the multi-ring arrangement while keeping similar spatial resolution throughout the FOV. [ABSTRACT FROM AUTHOR]

Abstract: Conventional PET scanners can image the whole body using many bed positions. On the other hand, an entire-body PET scanner with an extended axial FOV, which can trace whole-body uptake images at the same time and improve sensitivity dynamically, has been desired. The entire-body PET scanner would have to process a large amount of data effectively. As a result, the entire-body PET scanner has high dead time at a multiplex detector grouping process. Also, the entire-body PET scanner has many oblique line-of-responses. In this work, we study an efficient data acquisition for the entire-body PET scanner using the Monte Carlo simulation. The simulated entire-body PET scanner based on depth-of-interaction detectors has a 2016-mm axial field-of-view (FOV) and an 80-cm ring diameter. Since the entire-body PET scanner has higher single data loss than a conventional PET scanner at grouping circuits, the NECR of the entire-body PET scanner decreases. But, single data loss is mitigated by separating the axially arranged detector into multiple parts. Our choice of 3 groups of axially-arranged detectors has shown to increase the peak NECR by 41%. An appropriate choice of maximum ring difference (MRD) will also maintain the same high performance of sensitivity and high peak NECR while at the same time reduces the data size. The extremely-oblique line of response for large axial FOV does not contribute much to the performance of the scanner. The total sensitivity with full MRD increased only 15% than that with about half MRD. The peak NECR was saturated at about half MRD. The entire-body PET scanner promises to provide a large axial FOV and to have sufficient performance values without using the full data. [Copyright &y& Elsevier]

Several MRI-based attenuation correction methods have been reported for PET/MRI; these methods are expected to make efficient use of high-quality anatomical MRIs and reduce the radiation dose for PET/MRI scanning. The accuracy of the attenuation map (μ-map) from an MRI depends on the accuracy of tissue segmentation and the attenuation coefficients to be assigned (μ-values). In this study, we proposed an MRI-based μ-value estimation method with a non-rotational radiation source to construct a suitable μ-map for PET/MRI. The proposed method uses an accurately segmented tissue map, the partial path length of each tissue, and detected intensities of attenuated radiation from a fixed-position (rather than a rotating) radiation source to obtain the μ-map. We estimated the partial path length from a virtual blank scan of fixed-point radiation with the same scanner geometry using the known tissue map from MRI. The μ-values of every tissue were estimated by inverting a linear relationship involving the partial path lengths and measured radioactivity intensity. Validation of the proposed method was performed by calculating a fixed- point data set based upon real a real transmission scan. The root-mean-square error between the μ-values derived from a conventional transmission scan and those obtained with our proposed method were 2.4±1.4%, 17.4±9.1% and 6.6±4.3% for brain, bone and soft tissue other than brain, respectively. Although the error estimates for bone and soft tissue are not insignificant, the method we propose is able to estimate the brain μ-value accurately and it is this factor that most strongly affects the quantitative value of PET images because of the large volumetric ratio of the brain. [ABSTRACT FROM AUTHOR]

Waseda University and Tokyo Tech are developing a 50 kg-class small satellite, tentatively named INnovative Space Probe for Imaging R-process Emission (I N S P I R E), which is scheduled for launch in 2027. The primary detector of the satellite is a BOX-type Compton Camera (CC-Box) that enables to observe low energy gamma rays (30 keV − 200 keV) in pinhole mode and high energy gamma rays (150 keV − 3 MeV) in Compton mode. The CC-Box consists of a pixelized Ce:GAGG scintillator array using a depth-of-interaction (DOI) structure, which is optically coupled to an MPPC array. The Ce:GAGG arrays are also positioned on the side of detector to enhance its sensitivity. Herein, we describe the detailed design of the CC-Box, its data processing flow, and its weight and power specifications. We then assess the anticipated performance of the detector in terms of continuum and line sensitivities, together with a simulation of the Crab nebula observation. Finally, a brief review of the experimental results is performed using hands-on devices already implemented in nuclear medicine and atmospheric observations, such as gamma-ray imaging of thunderclouds. [ABSTRACT FROM AUTHOR]

Silicon photomultipliers (SiPMs) provide many advantages for PET detectors, such as their high internal gain, high photon detection efficiency and insensitivity to magnetic fields. The number of detectable scintillation photons of SiPMs, however, is limited by the number of microcells. Therefore, pulse height of PET detectors using SiPMs is saturated when large numbers of scintillation photons enter the SiPM pixels. On the other hand, we previously presented a depth-of-interaction (DOI) encoding method that is based on the light sharing method. Since our encoding method detects scintillation photons with multiple readout pixels, the saturation effect can be suppressed. We constructed two prototype four-layer DOI detectors using a SiPM array and evaluated their performances. The two prototype detectors consisted of four layers of a 6×6 array of Lu2(1−x)Y2x SiO5 (LYSO) crystals and a SiPM (multi-pixel photon detector, MPPC, Hamamatsu Photonics K.K.) array of 4×4 pixels. The size of each LYSO crystal element was 1.46mm×1.46mm×4.5mm and all surfaces of the crystal elements were chemically etched. We used two types of MPPCs. The first one had 3600 microcells and high photon detection efficiency (PDE). The other one had 14,400 microcells and lower PDE. In the evaluation experiment, all the crystals of the detector using the MPPC which had the high PDE were clearly identified. The respective energy and timing resolutions of lower than 15% and 1.0ns were achieved for each crystal element. No saturation of output signals was observed in the 511keV energy region due to suppression of the saturation effect by detecting scintillation photons with several MPPC pixels by the light sharing method. [ABSTRACT FROM AUTHOR]

We have been developing silicon-on-insulator (SOI) pixel detectors with a pinned depleted diode (PDD) structure, named "XRPIX", for X-ray astronomy. The PDD structure is formed in a thick p-type substrate, to which high negative voltage is applied to make it fully depleted. A pinned p-well is introduced at the backside of the insulator layer to reduce a dark current generation at the Si-SiO 2 interface and to fix the back-gate voltage of the SOI transistors. An n-well is further introduced between the p-well and the substrate to make a potential barrier between them and suppress a leakage current. An optimization study on the n-well dopant concentration is necessary because a higher dopant concentration could result in a higher potential barrier but also in a larger sense-node capacitance leading to a lower spectroscopic performance, and vice versa. Based on a device simulation, we fabricated five candidate chips having different n-well dopant concentrations. We successfully found out the best n-well design, which suppressed a large leakage current and showed satisfactory X-ray spectroscopic performance. Too low and too high n-well dopant concentration chips showed a large leakage current and degraded X-ray spectroscopic performance, respectively. We also found that the dependency of X-ray spectroscopic performance on the n-well dopant concentration can be largely explained by the difference in sense-node capacitance. [ABSTRACT FROM AUTHOR]

Abstract: Heat generation density of electric elements increases close to the limit of forced air-cooling. New cooling technology is required and a self-vibration heat pipe is proposed for the electric elements cooling. The self-vibration heat pipe, which has a meandering capillary channel, can operate for vertical and horizontal heat removal without gravity effects. However, the behaviors of the working fluid in the pipe have not been well studied. The purpose of this study is to clarify the working fluid phenomena in the heat pipe. The working fluid in the pipe was visualized by neutron radiography system at JRR-3 in Japan Atomic Energy Agency. The liquid columns in the meandering channel of the heat pipe were recorded by a high-speed camera. The obtained images were segmented and the meandering capillary channel was uncoiled by image processing methods to show the temporal vibration of the liquid columns in the stretched channel. Periods of the column oscillation were about 0.5–1.5s. The oscillation of the columns was analyzed by a mass-spring model. The periods of the oscillation were obtained and compared with the experiment results. It was shown that the analytical values agreed fairly with the experimental ones. [Copyright &y& Elsevier]

Abstract: In order to clarify the effects of water on performances of a Polymer Electrolyte Fuel Cell (PEFC), measurements of water distribution in a Japan Automobile Research Institute (JARI) standard PEFC were carried out by means of neutron radiography. Furthermore, the cell voltage and the pressure drop between inlet and outlet of the air were simultaneously measured. The effects of channel geometry, i.e. single-serpentine and three-serpentine, and relative humidity of air were investigated. The experimental conditions were current density of 200mA/cm2, hydrogen utilization of 9.5% and oxygen utilization of 40%. The membrane electrode assembly (MEA) area was 5×5cm2. The pictures were taken every 15s with an exposure time of 12s. The spatial resolution was 108μm. From the measurements, the relation between cell voltage, pressure drop and movement of the water plug in the channel was confirmed. The PEFC performances were recovered as the water plug evacuated. Condensed water in the channel decreased with the relative humidity of air. However, it may affect the MEA permanence. Therefore, the most appropriate operating conditions should be decided for taking into account both the cell performances and the permanencies. [Copyright &y& Elsevier]

Abstract: We are developing a small animal PET scanner, “jPET-RD” to achieve high sensitivity as well as high spatial resolution by using four-layer depth-of-interaction (DOI) detectors. The jPET-RD is designed with two detector rings. Each detector ring is composed of six DOI detectors arranged hexagonally. The diameter of the field-of-view (FOV) is 8.8cm, which is smaller than typical small animal PET scanners on the market now. Each detector module consists of a crystal block and a 256-channel flat panel position-sensitive photomultiplier tube. The crystal block, consisting of 32×32×4 crystal (4096 crystals, each 1.46mm×1.46mm×4.5mm) and a reflector, is mounted on the 256ch FP-PMT. In this study, we evaluated the spatial resolution of reconstructed images with the evaluation system of two four-layer DOI detectors which consist of 32×32×4 LYSO (Lu: 98%, Y: 2%) crystals coupled on the 256ch FP-PMT by using RTV rubber. The spatial resolution of 1.5mm was obtained at the center of the FOV by the filtered back projection. The spatial resolution, better than 2mm in the whole FOV, was also achieved with DOI while the spatial resolution without DOI was degraded to 3.3mm. [Copyright &y& Elsevier]

Abstract: Based on 10 years experience of carbon therapy at HIMAC, new facility project is in progress at NIRS. In this paper, the design of the synchrotron and its transport system dedicated for carbon therapy based on the machine study at HIMAC and the results of the studies are presented. © 2001 Elsevier Science. All rights reserved [Copyright &y& Elsevier]

Abstract: A new method for slow beam-extraction from a synchrotron ring is proposed, based on controlling a quadrupole field with a fast response (FQ), assisted by a transverse RF-field (RF-knockout). This method works as follows: (1) particles of a circulating beam are diffused by RF-knockout to just inside the boundary of a separatrix produced under a resonant condition, (2) exciting the FQ shrinks the separatrix to a certain size, and the particles outside the separatrix can be extracted, (3) the fast Q-field is turned off, and (4) the above process is repeated until all of the circulating beam is completely extracted. This method can extract prescribed particles at required timings quickly and precisely, because it is controlled with only the fast Q-field. A proof-of-principle experiment was carried out at the Heavy Ion Medical Accelerator in Chiba (HIMAC) synchrotron. As a result, it was verified that the beam was extracted only with exciting the FQ, but not with turning the RF-knockout on. [Copyright &y& Elsevier]