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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]

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]

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]

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]

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]

Silicon photomultipliers (SiPMs) have become a standard photodetector to be coupled with scintillators in PET, but the SiPM saturation is limiting the performance achievable with the detectors employed, in particular the high energy resolution which is necessary for whole gamma imaging (WGI). The concept of WGI combines PET and a Compton camera by inserting a scatterer detector ring into a PET ring. Not only typical SPECT radionuclides such as 99m Tc (140 keV), but also unusual positron emitters such as 89Zr (909 keV) and 44Sc (1157 keV) can be imaging targets. For better spatial resolution in Compton imaging, the scatterer detector requires better energy resolution for a wide range of deposited energies. The use of bright scintillators such as GAGG is essential, but the SiPM saturation may prevent full use being made for such bright scintillators. We expected that inserting a thick light guide between GAGG and SiPM could spread scintillation photons to surrounding SiPMs and eliminate the saturation effect. On the other hand, the thicker the light guide becomes, the greater the number of scintillation photons that may be absorbed. Therefore, in this paper, we investigated the relationship between the light guide thickness and the energy resolution. A 22 × 22 array of GAGG crystals (0.9 × 0. 9 × 6 mm3 each) was optically coupled to the 8 x 8 multi-pixel photon-counter (MPPC) array (3 × 3 mm2 pixel, 50 × 50 μ m 2 sub-pixel) via a light guide, for which thickness was changed from 0 (i.e., without the light guide) to 8 mm. Using point sources with different energies (133Ba, 22Na and 137Cs), we compared crystal identification performance, linearity of the output signal and energy resolution. Increasing the light guide thickness gradually degraded crystal identification performance but improved linearity of the output signals. Energy resolution at 81 keV constantly deteriorated with increasing light guide thickness. Energy resolutions at 356, 511 and 662 keV were improved with increasing light guide thickness to a certain value after which they deteriorated; the thicknesses at which deterioration started were 2.0 mm, 3.0 mm and 4.0 mm, respectively, for the energy resolutions at 356, 511 and 662 keV. We found that the optimum light guide thickness for the target energy range was 2.0 mm, and for this thickness, energy resolution values were 22.0% at 81 keV, 7.6% at 356 keV, 8.3% at 511 keV and 8.2% at 662 keV. [ABSTRACT FROM AUTHOR]

This study developed a novel method for detecting hypernuclear events recorded in nuclear emulsion sheets using machine learning techniques. The artificial neural network-based object detection model was trained on surrogate images created through Monte Carlo simulations and image-style transformations using generative adversarial networks. The performance of the proposed model was evaluated using α -decay events obtained from the J-PARC E07 emulsion data. The model achieved approximately twice the detection efficiency of conventional image processing and reduced the time spent on manual visual inspection by approximately 1/17. The established method was successfully applied to the detection of hypernuclear events. This approach is a state-of-the-art tool for discovering rare events recorded in nuclear emulsion sheets without any real data for training. [ABSTRACT FROM AUTHOR]

A 230 MeV superconducting azimuthally varying field (AVF) cyclotron SC230 was developed by Sumitomo Heavy Industries Ltd., Japan. With a yoke diameter, height and weight of 2.8 m, 1.7 m and 65 t, respectively, it is currently the most compact isochronous cyclotron for proton therapy. Size reduction was achieved by a high magnetic field using cryogen-free superconducting coils. It adopts not only a superconducting magnet, but also sectors with a narrow pole gap and large spiral angle, two dees with low power consumption, and beam extraction using the precessional extraction method. It has a maximum beam current of 1 μ A. The total power consumption of its system is lower than 200 kW. After each component, including the magnet, was fabricated, the cyclotron was moved to a new test site, and a vacuum test and conditioning of some components were conducted. The beam commissioning started, and the first extracted beam was successfully observed. In this paper, the processes and results of the beam commissioning and the basic performance of the first beam are reported. [ABSTRACT FROM AUTHOR]

To produce a 230 MeV proton beam, a new 4 T superconducting isochronous azimuthally varying-field (AVF) cyclotron, which is the smallest among AVF cyclotrons for proton beam therapy, is under development. In this project, to obtain the required field, a new mapping system was developed, and magnetic-field mapping and adjustments were conducted. The mapping system measures the field of the cyclotron using six Hall probes, whose positions are changed by a linear stage and a rotary stage. The results of field mapping tests conducted indicate that the system has sufficiently repeatability and reproducibility Further, the results of subsequent successful field measurements confirm that the field-adjustment methods are able to control the field. [ABSTRACT FROM AUTHOR]

We have developed a gas electron multiplier (GEM)-based time projection chamber (TPC) for the H-dibaryon search experiment at J-PARC. High-rate K − beam particles enter a TPC gas volume of approximately 0.2 m3, in a direction perpendicular to the electric field. A long-rectangular hollow section is located inside the TPC volume to accommodate a diamond target. We commissioned the TPC using 230-MeV protons with beam rates of up to 1 MHz. The TPC data acquisition system collected 5768 pad signals in full readout mode, with almost 100% efficiency, at a preset trigger rate of 230 Hz. We operated the TPC in an Ar/CH 4 gas mixture (90/10) without a magnetic field. The spatial resolutions on the pad plane are measured to be 400– 700 μ m , which correspond to 230– 300 μ m in a magnetic field of 1 T. We confirmed high tracking capability at beam rates of up to 1 MHz. [ABSTRACT FROM AUTHOR]

The quality and uniformity of positron emission tomography (PET) images can be improved significantly using a PET scanner, which has both time-of-flight (TOF) and depth-of-interaction (DOI) capabilities. We have already developed a DOI dual-end detector using segmented crystal bars by applying a subsurface laser engraving (SSLE) technique, and the DOI was determined by the ratio of the detected light between two readouts using the Anger calculation. In this study, we investigated the influence of the number of DOI segments on the performance of DOI identification and the coincidence timing performance of the detector. The detector consisted of a single lutetium fine silicate (LFS) crystal bar (3 × 3 × 20 mm3) with various numbers of DOI segments that were made by applying the SSLE technique and Hamamatsu silicon photomultiplier (SiPM) modules. The maximum number of DOI segments was six, and the SiPM module included one hundred forty-four 4 mm × 4 mm SiPM readouts. The coincidence resolving time (CRT) of each DOI segment was obtained from the side irradiation of the dual-end detector. All DOI segments of the detector with 2, 3, 4, 5 or 6 DOI segments were clearly identified, and average energy resolutions of 9.8 ± 0.5% and 12.5 ± 1.4% were obtained at the 511 keV photo peak for the detectors with 2 DOI and 6 DOI segments, respectively. The minimum and maximum estimated CRT of 180 ± 6 ps and 236 ± 6 ps were obtained for the detectors with 2 DOI and 6 DOI segments, respectively. Insignificant differences were observed between the CRT values of different segments of one detector. Greater CRT values were obtained for detectors with larger DOIs. The results of this study prove that there is a high potential for segmented crystal bars using the SSLE technique as a good candidate for PET scanners with TOF and DOI capabilities, which can significantly improve the quality of PET images. [ABSTRACT FROM AUTHOR]

We developed a pinhole type gamma camera, using a compact detector module of a pixelated CdTe semiconductor, which has suitable sensitivity and quantitative accuracy for low dose rate fields. In order to improve the sensitivity of the pinhole type semiconductor gamma camera, we adopted three methods: a signal processing method to set the discriminating level lower, a high sensitivity pinhole collimator and a smoothing image filter that improves the efficiency of the source identification. We tested basic performances of the developed gamma camera and carefully examined effects of the three methods. From the sensitivity test, we found that the effective sensitivity was about 21 times higher than that of the gamma camera for high dose rate fields which we had previously developed. We confirmed that the gamma camera had sufficient sensitivity and high quantitative accuracy; for example, a weak hot spot (0.9 μ Sv/h) around a tree root could be detected within 45 min in a low dose rate field test, and errors of measured dose rates with point sources were less than 7% in a dose rate accuracy test. [ABSTRACT FROM AUTHOR]

A new data acquisition system has been developed continually as a part of the development of a new beam loss monitor (BLM) system for the J-PARC main ring. This development includes a newly designed front-end isolation amp that uses photo-couplers and a VME-based new analog-to-digital converter (ADC) system. Compared to the old amp, the new amp has a 10 times higher conversion impedance for the input current to the output voltage; this value is 1 M Ω . Moreover, the bandwidth was improved to from DC to 50 kHz, which is about two orders of magnitude greater than the previously used bandwidth. The theoretical estimations made in this study roughly agree with the frequency response obtained for the new system. The new ADC system uses an on-board field-programmable gate array chip for signal processing. By replacing the firmware of this chip, changes pertaining to future accelerator upgrade plans may be introduced into the new ADC system; in addition, the ADC system can be used in other applications. The sampling speed of the system is 1 MS/s, and it exhibits a 95 dBc spurious-free dynamic range and 16.5 effective number of bits. The obtained waveform and integrated charge data are compared with two reference levels in the ADC system. If the data exceeds the reference level, the system generates an alarm to dump the beams. By using the new data acquisition system, it was proved that the new BLM system shows a wide dynamic range of 160 dB. In this study, the details of the new data acquisition system are described. [ABSTRACT FROM AUTHOR]

We report on the design and performance of a mixed-signal application specific integrated circuit (ASIC) dedicated to avalanche photodiodes (APDs) in order to detect hard X-ray emissions in a wide energy band onboard the International Space Station. To realize wide-band detection from 20 keV to 1 MeV, we use Ce:GAGG scintillators, each coupled to an APD, with low-noise front-end electronics capable of achieving a minimum energy detection threshold of 20 keV. The developed ASIC has the ability to read out 32-channel APD signals using 0.35 μ m CMOS technology, and an analog amplifier at the input stage is designed to suppress the capacitive noise primarily arising from the large detector capacitance of the APDs. The ASIC achieves a performance of 2099 e − + 1.5 e − /pF at root mean square (RMS) with a wide 300 fC dynamic range. Coupling a reverse-type APD with a Ce:GAGG scintillator, we obtain an energy resolution of 6.7% (FWHM) at 662 keV and a minimum detectable energy of 20 keV at room temperature (20 °C). Furthermore, we examine the radiation tolerance for space applications by using a 90 MeV proton beam, confirming that the ASIC is free of single-event effects and can operate properly without serious degradation in analog and digital processing. [ABSTRACT FROM AUTHOR]

We have constructed a conduction-cooled superconducting dipole magnet for the Hyperon spectrometer at Japan Proton Accelerator Research Complex (J-PARC). The magnet is a Helmholtz-type dipole magnet with two circular coils with a radius of 500 mm separated by 500 mm. It provides a uniform magnetic field of 1.0 T or higher in a volume of ϕ 600 mm × 600 mm, covering the drift region of a time projection chamber (TPC). Owing to the target location inside the TPC, the Hyperon spectrometer has a broad angular coverage with a nearly 2 π solid angle. We have successfully excited the magnet up to 1.3 T. At 1.0 T, we operated it stably for more than 1 week in single-magnet configuration and double-magnet configuration with a normal-conducting 0.7-T dipole magnet located 30 cm apart. The measured magnetic field distribution in the TPC volume is consistent with the calculated field map. [ABSTRACT FROM AUTHOR]

An automatic track following system has been successfully developed to follow tracks in nuclear emulsion sheets exposed with beam up to the limit to be observed for the first time. The track followed rate of the system is 99.5% with the assistance of the new techniques. The working speed for a track is less than 1 min through one thick emulsion sheet, whereas it is 15 times faster than that of semiautomatic system with human. The system working for 24 h is applied for the E07 experiment at J-PARC and makes it possible to detect ~10 2 nuclei with double strangeness (S=−2 nuclei) within one year. Regarding analyses to identify nuclear species of S=−2 nuclei, the system shows quite decent job for significant steps such as following tracks emitted to spherical directions from S=−2 nuclei, measurement of lengths of followed tracks, and so on. [ABSTRACT FROM AUTHOR]

A new timing detector has been developed to measure ∼50 MeV/c positrons with a time resolution of σ t ≃ 30 ps in the MEG II experiment. The detector are segmented into 512 scintillation counters, each of which consists of 120 × ( 40 or 50 ) × 5 mm 3 size BC-422 and two arrays of six AdvanSiD silicon photomultipliers. The single-counter resolutions are measured to be 70–80 ps. The counter layout is optimized to get the maximum number of hit counters (on average 9 for signal positrons). This multiple-counters measurement leads to a significant improvement in the time resolution down to 30 ps. Using the first one-fourth (128) counters, a pilot run was carried out using the MEG II beam of 7 × 10 7 μ + / s and the basic functionality was tested. [ABSTRACT FROM AUTHOR]

We developed an add-on PET which was a PET insert based on 4-layered depth-of-interaction (DOI) detectors integrated with a birdcage RF-coil. The PET detectors were placed close to subjects to achieve high sensitivity. The DOI capability suppress degradation of spatial resolution at the edge of the field of view (FOV). Previously, we developed an first prototype which had a short axial FOV. In order to extend the axial FOV, we developed new scalable add-on PET prototype. The constructed RF-coil of the new prototype was combined with 2 PET detector units Each detector unit with two PET detectors was shielded with a carbon fiber shielding box. Each PET detector consisted of a 14 × 14 × 4-layer array of lutetium fine silicate crystals (1.9 mm × 1.9 mm × 4.0 mm), an 8 × 8 multi-pixel photon counter (MPPC, S12641PA-050) array and a readout circuit board with an ASIC. The RF coil was tuned for a 3T clinical MRI (MAGNETOM Verio, Siemens). We evaluated performance the scalable add-on PET prototype in simultaneous PET/MRI measurements. We obtained spatial resolutions of 2.0 mm at the center of the FOV and better than 3.3 mm in the whole FOV. The energy resolution of 12.4 % was obtained at 511 keV. In addition, we observed no degradation of PET performance caused by the MRI measurement. The signal-to-noise ratio (SNR) of the MRI image was 186.2 in simultaneous measurements with the PET. The maximum Δ B 0 and maximum difference of the secondary magnetic field due to the eddy current effect were smaller than 0.2 ppm and ± 1. 0 μ T, respectively. It meant that the influence of the PET detectors on the static magnetic field and secondary magnetic field did not cause problems. [ABSTRACT FROM AUTHOR]

We tested a plastic-scintillator (PS) bar for the forward time-of-flight (TOF) detector of the J-PARC E50 spectrometer using a 740-MeV/ c positron beam. The bar is composed of Saint-Gobain Crystals (BC-420), with a 30 mm × 40 mm cross section and 1800-mm length. Each side of the bar is connected to a metal-packaged photomultiplier tube (PMT), Hamamatsu H11934-200 with an ultra-bialkali (UBA) photoelectric surface. The PMTs have an advanced feature of a small spread of the electron transit time (0. 27 ns) and high quantum efficiency (≈ 43 %). The intrinsic resolutions for the timing measurement using the two PMTs connected to both the ends are found to be 0.053 and 0.059 ns in the standard deviation for the 40- and 30-mm-thick penetrations at the center, respectively. The results show that metal-packaged PMTs enable TOF measurements using an ordinary hodoscope consisting of 1.8-m-long PS bars with an excellent time resolution (∼ 0. 06 ns in the standard deviation). [ABSTRACT FROM AUTHOR]

The development of a Timing Counter detector designed for the MEGII upgrade of the MEG experiment, which strives to improve the sensitivity on the μ + → e + γ decay of an order of magnitude, is presented. It is based on two sets of counters (sectors) arranged on a semi-cylindrical structure; each sector consists of 256 counters. Each counter consists of tile of fast scintillator with a dual-side read-out based on SiPM arrays in series connection. The high granularity has two advantages: optimized size for achieving high resolution (75 ps) for the single counter, and a signal e + crosses several counters, so that resolution improves by averaging multiple time measurements. A prototype has been built and tested both in BTF and PSI facilities in order to prove the multi-hit scheme in MEG-like beam conditions. A 35 ps resolution with eight hits has been obtained with a e + beam at 100 kHz. The first sector will be tested in the MEG II pre-engineering run planned at the end of 2015. [ABSTRACT FROM AUTHOR]

We have developed a novel low-cost gamma-ray imaging Compton camera γI that has a high detection efficiency. Our motivation for the development of this detector was to measure the arrival directions of gamma rays produced by radioactive nuclides that were released by the Fukushima Daiichi nuclear power plant accident in 2011. The detector comprises two arrays of inorganic scintillation detectors, which act as a scatterer and an absorber. Each array has eight scintillation detectors, each comprising a large CsI (Tl) scintillator cube of side 3.5 cm, which is inexpensive and has a good energy resolution. Energies deposited by the Compton scattered electrons and subsequent photoelectric absorption, measured by each scintillation counter, are used for image reconstruction. The angular resolution was found to be 3.5° after using an image-sharpening technique. With this angular resolution, we can resolve a 1 m 2 radiation hot spot that is located at a distance of 10 m from the detector with a wide field of view of 1 sr. Moreover, the detection efficiency 0.68 cps/MBq at 1 m for 662 keV (7.6 cps/μSv/h) is sufficient for measuring low-level contamination (i.e., less than 1 μSv/h) corresponding to typical values in large areas of eastern Japan. In addition to the laboratory tests, the imaging capability of our detector was verified in various regions with dose rates less than 1 μSv/h (e.g., Fukushima city). [ABSTRACT FROM AUTHOR]

The liquid xenon (LXe) γ-ray detector for the MEG II experiment is based on a highly granular scintillation readout with Multi-Pixel Photon Counters (MPPCs). Here we report on the development of a large-area MPPC sensitive to LXe scintillation light in deep-UV range for the MEG II LXe detector. A prototype model of the deep-UV MPPC with an active area of 12 × 12 mm 2 was successfully tested in LXe, showing an excellent performance such as a high photon detection efficiency for the LXe scintillation light (about 20% at Δ V = 2.5 V ), a high internal gain (about 10 6 at Δ V = 2.5 V ) and an excellent single photoelectron resolution. The sensor chip of the MPPC is segmented into four sectors, which are then connected in series in order to reduce the overall sensor capacitance. The signal fall time of about 135 ns for the non-segmented sensor was significantly reduced down to 25 ns with the series-connected sensor segments. The preliminary results on the performance of the deep-UV MPPC are presented. [ABSTRACT FROM AUTHOR]

The Belle II detector, a follow up of the very successful Belle experiment, is under construction at the SuperKEKB electron–positron collider at KEK in Japan. For the PID system in the forward region of the spectrometer, a proximity-focusing ring-imaging Cherenkov counter with an aerogel radiator is being developed. For the position sensitive photon sensor, a 144-channel Hybrid Avalanche Photo-Detector has been developed with Hamamatsu Photonics K.K. In this report, we describe the specification of the Hybrid Avalanche Photo-Detector and the status of the mass production. [ABSTRACT FROM AUTHOR]

A time-stamping system for nuclear physics experiments has been introduced at the RIKEN Radioactive Isotope Beam Factory. Individual trigger signals can be applied for separate data acquisition (DAQ) systems. After the measurements are complete, separately taken data are merged based on the time-stamp information. In a typical experiment, coincidence trigger signals are formed from multiple detectors to take desired events only. The time-stamping system allows the use of minimum bias triggers. Since coincidence conditions are given by software, a variety of physics events can be flexibly identified. The live time for a DAQ system is important when attempting to determine reaction cross-sections. However, the combined live time for separate DAQ systems is not clearly known because it depends not only on the DAQ dead time but also on the coincidence conditions. Using the proposed time-stamping system, all trigger timings can be acquired, so that the combined live time can be easily determined. The combined live time is also estimated using Monte Carlo simulations, and the results are compared with the directly measured values in order to assess the accuracy of the simulation. [ABSTRACT FROM AUTHOR]

The Belle II spectrometer, a follow up of the very successful Belle experiment, is under construction at the SuperKEKB electron–positron collider at KEK in Japan. For the PID system in the forward region of the spectrometer, a proximity focusing ring-imaging Cherenkov (RICH) counter with an aerogel radiator is being developed. The counter will provide a 4σ separation of pions and kaons up to momenta of 4 GeV/ c . For the position sensitive photon sensor, a 144-channel Hybrid Avalanche Photo-Detector (HAPD) has been developed with Hamamatsu Photonics K.K. The readout electronics is based on the custom developed ASIC. The design of the components is currently being finalized and part of their mass production have already started. Herein, we report the final design of the counter and a prototype test conducted with test beams at DESY. [ABSTRACT FROM AUTHOR]

A proximity focusing RICH will be installed in the forward direction of the Belle II spectrometer, inside a super conducting solenoid coil with the magnetic field of 1.5 T. Photons emitted in the sequence of two different aerogel radiator layers will be registered by the Hybrid Avalanche Photo Diodes. By detecting more than 11 photons per incident 4 GeV/ c pion, with 15 mrad single photon Cherenkov angle resolution, the designed detector should enable an efficient separation of kaons from pions in the wide range of particle momenta from 0.5 GeV/ c up to 4 GeV/ c . The particle separation will be based on a two-dimensional extended maximum-likelihood analysis. The position dependence of the efficiencies for identification of pions and kaons shows a very homogeneous response over the detector area. The performance on the edge of the detector is improved by employing planar mirrors to reflect the Cherenkov photons on the detector plane. The results show that by using a designed detector configuration the kaon pion separation efficiency of more than 95% can be achieved at a very low pion misidentification probability of 1%. In the low momentum region (0.5 GeV/ c –0.8 GeV/ c ) the variation of detected number of photons due to matching of aerogel refractive index and the gaps between the sensitive areas on the detector plane results in a slightly decreased separation efficiency. [ABSTRACT FROM AUTHOR]

This paper presents recent progress in the development and mass production of large-area hydrophobic silica aerogels for use as radiators in the aerogel-based ring-imaging Cherenkov (A-RICH) counter, which will be installed in the forward end cap of the Belle II detector. The proximity-focusing A-RICH system is especially designed to identify charged kaons and pions. The refractive index of the installed aerogel Cherenkov radiators is approximately 1.05, and we aim for a separation capability exceeding 4 σ at momenta up to 4 GeV/ c . Large-area aerogel tiles (over 18×18×2 cm 3 ) were first fabricated in test productions by pin drying in addition to conventional methods. We proposed to fill the large end-cap region (area 3.5 m 2 ) with 124 water-jet-trimmed fan-shaped dual-layer-focusing aerogel combinations of different refractive indices (1.045 and 1.055). Guided by the test production results, we decided to manufacture aerogels by the conventional method and are currently proceeding with mass production. In an electron beam test undertaken at the DESY, we confirmed that the K / π separation capability of a prototype A-RICH counter exceeded 4 σ at 4 GeV/ c . [ABSTRACT FROM AUTHOR]

Abstract: We are developing a PET-MRI system which consists of PET detectors integrated with the head coil of the MRI in order to realize high spatial resolution and high sensitivity in simultaneous measurements. In the PET-MRI system, the PET detectors which consist of a scintillator block, photo-detectors and front-end circuits with four-layer depth-of-interaction (DOI) encoding capability are placed close to the measured object. Therefore, the proposed system can achieve high sensitivity without degradation of spatial resolution at the edge of the field-of-view due to parallax error thanks to the four-layer DOI capability. In this paper, we fabricated a prototype system which consists of a prototype four-layer DOI-PET detector, a dummy PET detector and a prototype birdcage type head coil. Then we used the prototype system to evaluate the performance of the four-layer DOI-PET detector and the reciprocal influence between the PET detectors and MRI images. The prototype DOI-PET detector consists of six monolithic multi-pixel photon counter (MPPC) arrays (S11064-050P), a readout circuit board, two scintillator blocks and a copper shielding box. Each scintillator block consists of four layers of Lu1.8Gd0.2SiO5:Ce (LGSO) scintillators and reflectors are inserted between the scintillation crystals. The dummy detector has all these components except the two scintillator blocks. The head coil is dedicated to a 3.0T MRI (MAGNETOM Verio, Siemens) and the two detectors are mounted in gaps between head coil elements. Energy resolution and crystal identification performance of the prototype four-layer DOI-PET detector were evaluated with and without MRI measurements by the gradient echo and spin echo methods. We identified crystal elements in all four layers from a 2D flood histogram and energy resolution of 15–18% was obtained for single crystal elements in simultaneous measurements. The difference between the average energy resolutions and photo-peak positions with and without MRI measurements was lower than 0.3 percentage points and 1.7% for all layers. The results indicated that these performances were sufficient as PET detectors for the proposed PET-MRI system and there was no influence from the MRI measurements on the PET imaging in the simultaneous measurements. The signal-to-noise ratio of the MRI image and static magnetic field of the MRI were also evaluated with and without measurements of the PET detectors. The maximum decrease of the static magnetic field due to the LGSO scintillators was approximately 1ppm. The signal-to-noise ratio decreased from 242.80 without the PET detector to 44.948 in simultaneous measurements. [Copyright &y& Elsevier]

Abstract: A new type of a trigger-scintillation counter array designed for the MTV experiment at TRIUMF-ISAC has been developed, which uses aluminum-metallized film tape for wrapping to achieve the required assembling precision of ±0.5mm. The MTV experiment uses a cylindrical drift chamber (CDC) as the main electron-tracking detector. The barrel-type trigger counter is placed inside the CDC to generate a trigger signal using 1mm thick, 300mm long thin plastic scintillation counters. Detection efficiency and light attenuation compared with conventional wrapping materials are studied. [Copyright &y& Elsevier]

The performance of a small prototype of a cylindrical drift chamber (CDC) used in the COMET Phase-I experiment was studied by using an electron beam. The prototype chamber was constructed with alternating all-stereo wire configuration and operated with the He − iC 4 H 10 (90/10) gas mixture without a magnetic field. The drift space–time relation, drift velocity, d E /d x resolution, hit efficiency, and spatial resolution as a function of distance from the wire were investigated. The average spatial resolution of 150 μ m with the hit efficiency of 99% was obtained at applied voltages higher than 1800 V. We have demonstrated that the design and gas mixture of the prototype match the operation of the COMET CDC. [ABSTRACT FROM AUTHOR]

The MEGII Timing Counter will measure the positron time of arrival with a resolution of ~ 30 ps relying on two arrays of scintillator pixels read out by 6144 Silicon Photomultipliers (SiPMs) from AdvanSiD. They are characterised, measuring their breakdown voltage, to assure that the gains of the SiPMs of each pixel are as uniform as possible, to maximise the pixel resolution. Gain measurements have also been performed. [ABSTRACT FROM AUTHOR]

The COMET Phase-I experiment plans to search for muon to electron conversion. In order to get a good signal-to-noise ratio and time resolution, all the front-end readout boards are installed near the detector region where the radiation level is high. The radiation effects, in particular from neutrons, onto FPGA hardware will be a severe problem. We developed high reliable firmware with auto-recovery schemes for three different series of FPGAs, and evaluated them with a neutron beam. In these tests, soft error rates were measured and good performances of the schemes were demonstrated. [ABSTRACT FROM AUTHOR]

At the Belle II experiment, Aerogel RICH is used as the particle identification device that covers the forward end-cap part of the Belle II detector. We develop the readout system of Hybrid Avalanche Photo Detectors that are used as the photon sensors of the Aerogel RICH. We present overview of the readout system, and report the status of the mass production toward the Belle II experiment. [ABSTRACT FROM AUTHOR]

A hybrid photo-detector (HAPD) has been developed for the aerogel RICH (ARICH) of the Belle II experiment. In the present contribution we report the performance tests in magnetic fields, results of the neutron and gamma irradiation studies, and of aging tests. We also review the production status and plans. [ABSTRACT FROM AUTHOR]

CsI(Tl) scintillation detectors based on a silicon photomultiplier (SiPM) were tested for low-energy proton detection. Pulse shape analysis of the SiPM signals with a transimpedance amplifier was conducted to investigate the saturation effect due to the recovery time of a pixel and to evaluate particle identification capability. To recover energy linearity, a saturation correction method based on a non-paralyzable dead time model was proposed. The setup using the SiPM with a 25 μ m pixel pitch well separated protons and deuterons at energies from 3 to 12 MeV. Additionally, a readout circuit without an amplifier was tested to investigate another type of saturation due to the voltage drop effect. [ABSTRACT FROM AUTHOR]

A method for controlling the energy of slowed-down RI beams with the goal energy of 20 MeV/u was developed at the RIKEN RI Beam Factory. The 93Zr beam energy was successfully tuned to 20.2 MeV/u in a single step by adjusting its momentum selected by the first dipole magnet after a primary target. A method for particle identification was developed for the secondary reaction fragments at 50 MeV/u. The dispersive mode was applied to the ZeroDegree spectrometer to measure the momentum at the final focus F11. The reaction fragments were stopped in the multi-sampling ionization chamber (MUSIC) placed at F11, which measured the Δ E − E of the beam particles. In addition, the range R in MUSIC was determined with a resolution of 1.4 mm (σ) by using the energy ratio obtained from multi-sampled energy deposits. The atomic number was determined from the E − R correlation with a resolution of 0.15 (σ). To distinguish the charge state of the RI beam after the secondary reaction target, the range with the correction for the β dependence was combined with the mass-to-charge ratio determined from the time-of-flight and magnetic-rigidity measurements. A 5.6 σ separation was obtained between 92Zr 40 + and 90Zr 39 + using these two values. [ABSTRACT FROM AUTHOR]

Nuclear emulsion is a film-type charged particle track detector that uses the technology of silver halide photosensitive material. Because nuclear emulsion is compact and does not require an electric power source, it is suitable as a detector for cosmic-ray imaging (also called cosmic-ray muon radiography or muography) that requires outdoor observation. However, problems with the long-term stability and temperature tolerance of nuclear emulsion limit the observation periods, seasons and locations where it might be used. To enable long-term observation and outdoor use throughout the year, we investigated factors that affect the long-term characteristics of nuclear emulsion. The results of our experiments clearly showed that gelatin, additive chemicals, and packing material affect the long-term stability. Based on these results, we have developed a nuclear emulsion with excellent long-term stability. To confirm the properties of this newly developed nuclear emulsion, we examined the temperature dependence, and created an Arrhenius plot of the reaction rate. The prediction based on Arrhenius law showed that the Grain Density stayed at 25/ 100 μ m or more for more than one year at 10 °C and 20 °C, and for 260 days at 30 °C; and the Fog Density stayed at 5/ 1000 μ m 3 or less for more than one year at 10 °C and 20 °C, and for 270 days at 30 °C. This represents a new nuclear emulsion that is not limited by the observation period, season, and location. In fact, the developed stable nuclear emulsion is being used for cosmic-ray imaging observations in the pyramid of Khufu and is expected to be used for future cosmic-ray imaging observations and other elementary particle research. [ABSTRACT FROM AUTHOR]

AXEL is a high-pressure xenon gas time projection chamber for neutrinoless double-beta decay (0 ν 2 β) search. The AXEL has a unique readout system called ELCC which has a cellular structure and photosensors to detect electroluminescence light produced by ionization electrons. We demonstrated the performance of the ELCC with a small prototype detector (AXEL-HP10L). The obtained energy resolution corresponds to 0. 82 − 1. 74 % (FWHM) at the 0 ν 2 β Q-value. We are constructing a new prototype (AXEL-HP180L) in order to study the energy resolution at the Q-value of 0 ν 2 β with a new design of ELCC with unit structure, newly developed electronics board, field-shaping electrodes, and Cockcroft–Walton-type high voltage power supply. For a future 1-ton scale large AXEL detector, we are developing new background-reduction techniques; topology identification with machine learning, positive-ion detection, and active-shield options. [ABSTRACT FROM AUTHOR]

The current status of laboratory for Dark Matter search at the Kamioka mine and specialized facility for production of NaI(Tl) detectors is described. Techniques developed for purification and growth of ultra-low background NaI(Tl) crystals are reported. Achieved activity levels of the 210Pb, 40K, 238U, 232Th isotopes in the latest NaI(Tl) Dark Matter detector prototypes and the DAMA/LIBRA detectors are compared. [ABSTRACT FROM AUTHOR]

Radiation damage on front-end readout and trigger electronics is an important issue in the COMET Phase-I experiment at J-PARC, which plans to search for the neutrinoless transition of a muon to an electron. To produce an intense muon beam, a high-power proton beam impinges on a graphite target, resulting in a high-radiation environment. We require radiation tolerance to a total dose of 1. 0 kGy and 1 MeV equivalent neutron fluence of 1. 0 × 10 12 n eq cm − 2 including a safety factor of 5 over the duration of the physics measurement. The use of commercially-available electronics components which have high radiation tolerance, if such components can be secured, is desirable in such an environment. The radiation hardness of commercial electronic components has been evaluated in gamma-ray and neutron irradiation tests. As results of these tests, voltage regulators, ADCs, DACs, and several other components were found to have enough tolerance to both gamma-ray and neutron irradiation at the level we require. [ABSTRACT FROM AUTHOR]

Research on the distribution and dynamics of photoassimilates in plants, especially those in fruits, is important for increasing food production. Positron emission tomography (PET) and carbon-11 (11C) can be used for obtaining 3-D images of photoassimilates. For plant experiments, however, it is important to adjust the system to the plant's growth environment. A small OpenPET prototype can visualize an open space between two detector rings, and thus facilitate adjustment of the environment around a target plant during fruit PET imaging. In this work, we improve the OpenPET for plant studies and discuss its applications in the analysis of the dynamics and distributions of photoassimilates in plants with fruits. 11C-labeled photoassimilate translocation into the fruit of a strawberry plant is imaged using 11C-labeled CO 2 and the OpenPET. The OpenPET has been found to be promising for researching the physiological functions of the photoassimilates in plants with fruits. [ABSTRACT FROM AUTHOR]

We have developed a new laser-based time calibration system for highly segmented scintillator counters like the MEG II pixelated Timing Counter (pTC), consisting of 512 centimetre-scale scintillator counters read out by silicon photomultipliers (SiPMs). It is difficult to apply previous laser-based calibration methods for conventional metre-scale Time-Of-Flight detectors to the MEG II pTC from the implementation and the accuracy points of view. This paper presents a new laser-based time calibration system which can overcome such difficulties. A laser pulse is split into each scintillator counter via several optical components so that we can directly measure the time offset of each counter relative to the laser-emitted time. We carefully tested all the components and procedures prior to the actual operation. The laser system was installed into the pTC and thoroughly tested under the real experimental condition. The system showed good stability and being sensitive to any change of timing larger than ∼ 10 ps. Moreover, it showed an uncertainty of 48 ps in the determination of the time offsets, which meets our requirements. The new method provides an example of the implementation of a precise timing alignment for the new type of detectors enabled by the advance of SiPM technology. [ABSTRACT FROM AUTHOR]