[en] For a long time the Segmented Wire Ion Chamber (SWIC) was used for the beam profile measurement at external beam lines of the KEK 12 GeV Proton Synchrotron (KEK-PS). The Segmented Parallel-Plate Ion Chamber (SPIC) was initially developed for the replacement of SWIC. Unfortunately, at the KEK-PS, lifetime of the SWIC was not sufficiently long because of the frequent wire break. Therefore, finally, SPICs were developed for the beam profile measurements. Anode wire planes of the SWIC were replaced by printed Copper pattern planes on the flexible thin polyimide film and cathode wire plane was replaced by thin metallic mesh. It means that wires were completely removed from the SWIC and no wire was used in SPIC. The development of SPIC made the mean lifetime of the beam profile monitors of the KEK-PS sufficiently long. In addition, the production cost for one SPIC became very cheap and was almost one tenth (10%) of SWIC. Thus the number of the beam profile monitors at the external beam lines at the KEK-PS could be increased drastically. As a result, beam tuning of the external beam became much precise. For example, at the K2K experiment (KEK to Kamioka long baseline neutrino oscillation experiment), we constructed 300 m long primary proton beam line in order to bend primary protons to SuperKAMIOKANDE direction. Then 30 SPICs were successfully installed and operated in the new primary proton beam line without any technical and financial difficulties. Also for the K2K experiment, we had to measure the beam profile of muons which were generated by the two body decay of π -> μ + ν. The profile of the muons is exactly same as the profile of neutrinos. For the muon beam profile measurement, however, we had to prepare a kind of large scale SPIC whose size was 2 m x 2m. The wire-less structure of SPIC enabled us to enlarge the size of the ion chamber easily. And also, new anode electrode pattern so called ”Chidori pattern” was introduced for this large scale muon profile monitors. By using the Chidori pattern, two-dimensional information of the beam profile could be obtained by one parallel plane! This large-scale ion chamber worked stably during the K2K experiment and successfully kept the direction of the neutrino beam to SuperKAMIOKANDE within 1 mrad. The final trial of the ion chamber R&D was the introduction of the drift read out of electrons and ions. This drift read out technology was firstly used for the Bragg Curve Counter in order to measure the atomic number, z, and the total kinetic energy, E, of Intermediate Mass Fragments (IMFs) produced in the nuclear multifragmentation reactions caused by high energy primary protons hitting on the heavy nuclear target. Later, this drift read out technology was used for the residual gas ion beam profile monitors (RGIBM), which was prepared for the profile measurement of very high intensity primary proton beam extracted from the J-PARC 30GeV MR Accelerator. (author)

[en] A chemical vapor deposition (CVD) diamond detector is an attractive semiconductor detector owing to its advantages, such as large bandgap, high electron-hole mobility, low leakage current, excellent timing resolution, and outstanding radiation hardness. In particular, the low gamma sensitivity and outstanding radiation hardness of a diamond detector make it a suitable candidate for neutron measurements in harsh radiation environments, such as the Fukushima Daiichi nuclear power plant, Super KEKB, J-PARC, and LHC. In this work, the results of a study on the gamma sensitivity of diamond neutron detectors are reported. The responses of two diamond detectors of thicknesses 25 μm and 140 μm, respectively, to gamma rays were simulated and measured for high-activity ¹³⁷Cs and ⁶⁰Co gamma-ray sources. The maximum energy depositions of the 25-μm-thick diamond detector were approximately two-thirds and half of those of the 140-μm-thick diamond detector for ¹³⁷Cs and ⁶⁰Co gamma rays, respectively. The gamma-ray detection efficiencies of the two diamond detectors were measured by setting the threshold of the energy depositions to 0.058 MeV. The detection efficiencies of the 140-μm-thick diamond detector were approximately six and nine times higher than those of the 25-μm-thick one for ¹³⁷Cs and ⁶⁰Co gamma rays, respectively. (author)

[en] A Crookes tube is the oldest fundamental X-ray device, used by Roentgen in early studies on radiation. It is a type of discharge tube, usually used with an induction coil as a power supply. By applying a voltage of several tens of kV between the cathode and the anode in the tube, the cations in the evacuated tube are accelerated and impact the cathode, which displace secondary electrons. These electrons emitted by the cold cathode are accelerated to collide with a glass tube to create a bremsstrahlung X-ray. During demonstrations and experiments using a Crookes tube, teachers and participating students may be exposed to X-ray radiation. The use of radiation in teaching environments should adhere strictly to the guidelines of laboratory procedures to prevent undesirable exposure and to not exceed the safety limits regarding effective dose for teachers or students. Crookes tubes have been used as fundamental equipment for science education in junior-high schools in Japan. In addition, a following course of study was published in 2017 by MEXT, which requires understanding the nature of radiation related to cathode-rays. Regarding this issue, some studies on radiation safety involving the teaching of natural sciences using the Crookes tubes have been performed. An assessment conducted on some Crookes tubes showed that X-rays emitted by Crookes tubes produce very low energy (approximately 20 keV). However, the 1 cm dose equivalent was remarkably high (up to 143 mSv/h at 5 cm). This caused a maximum dose (H_p(10)) of 0.15 mSv per experiment for students, which is higher than the recommended value of 0.05 mSv per experiment in ICRP publication 36. Another study indicated that there was a distribution of leakage dose caused by scattered photons in all directions from the Crookes tube, but the investigation of X-ray energy was not performed. Radiation protection and safety guidelines have not been evaluated sufficiently to date. Estimations of the X-rays radiated from the Crookes tubes under various systematic conditions are required to establish these guidelines. The measurement of the X-ray energy spectrum from the Crookes tube and the dose estimate are considered difficult to perform because the X-ray energy is very low. There are lots of X-rays emitted from the Crookes tube using the induction coil in a short time. Therefore, the X-ray signal piles up. Consequently, it is difficult to evaluate X-rays using general measuring instruments. In this study, we measure X-rays using BaF₂ scintillator for time axis evaluation. (author)

[en] Scintillators are used in various field such as medical imaging like Positron Emission Tomography (PET) and radiation detector to detect gamma rays, and gamma-ray stopping power is one of the important factors to use as scintillator of PET. The stopping power or detection efficiency for gamma rays is proportional to (Z_eff)^a, where Z_eff is effective atomic number and a=4-5. Hf-based materials, like SrHfO₃ doped with Ce, are attractive materials with high effective atomic numbers. However, it is difficult to grow the crystal of such materials from the conventional melt growth techniques using crucibles, because Hf-based materials have higher melting points than softening or melting point (m. p.) of crucibles (i.e. Ir: m.p.:2447℃). Although Skull-melting technique realize to grow such materials, this technique is not optimized for material search due to long growth period and usage of much raw materials. For material search in higher melting points than the melting point of Ir, we propose a novel growth technique “Core Heating (CH) method”; the raw material powder is melted by melt Ir or other metal heated with electric arc in the furnace. As a feasibility test of the novel technique, we fabricated the conventional material, (Y_0.99 Ce_0.01)₃Al₅O₁₂ (Ce:YAG, m.p.:∼1970℃), which can be grown by the conventional melt growth technique like micro-pulling down (μ-PD) method. In this paper, we compared scintillation properties for Ce:YAG prepared by this novel technique and μ-PD method. Ce:YAG samples were grown by the CH method and μ-PD method. In the former technique, Ir was placed to contact with sintered Ce:YAG pellet, and we irradiated electric arc to Ir to obtain Ir-melt. The Ce:YAG pellet was heated by the Ir-melt. After Ce:YAG pellet melted, we gradually weakened the output of electric arc, and turned off. Melted pellet was cooled down slowly by the residual heat of Ir, and transparent crystals were grown. After both samples were cut and polish, we evaluated several optical and scintillation properties such as transmittance, luminescent properties, decay time and light output. To compare the light outputs, pulse height spectra of the Ce:YAG crystals grown by the both methods were measured excited by 662-keV gamma-rays from a ¹³⁷Cs source. The light output of Ce:YAG crystal grown by the CH method was similar to Ce:YAG crystal grown by the μ-PD method. Therefore, we have found CH method is useful as a material search method for scintillation materials with high melting points. (author)

[en] The detection efficiencies of six organic liquid scintillators were determined from experiments performed at High Energy Accelerator Research Organization (KEK), to study the photo-neutron produced from 16.95 MeV photons interacting with an Au target. The high energy part of efficiencies was obtained from ScinfulQMD calculation. The low energy part of efficiencies was obtained from ²⁵²Cf measurements. These two parts were connected with considering an absolute sensitivity of detectors to make efficiencies covering entire energy region. The efficiencies were tested through ²⁵²Cf fission neutron measurements. After the test, the efficiencies were applied in the data analysis of double-differential cross-section measurements of the ¹⁹⁷Au(γ,xn)^* reaction. (author)

[en] Energy-resolved X-ray computed tomography (ER-CT), which uses the energy information of X-rays passed through a phantom, is useful for detailed material identification in CT measurement. We have been studied ER-CT using a transXend detector that measurement X-rays as electric current and obtained energy information by analysis. Recently, ER-CT measurement is performed by a two-dimensional transXend detector consisting of a commercially available two-dimensional detector and a filter changing device. This method, however, requires many CT scans as the number of filters employed, brings problem of increased dose exposure. In order to solve this problem, we developed a CT measurement method to perform transmission measurements with changing filters in a small angle of phantom rotation and make them as a data set for ER-CT at a certain angle of the phantom. In this paper, we show by calculation that this method can be applied for a human-size phantom with a diameter of 300 mm. (author)

[en] For computed tomography measurement with low dose exposure, we developed a novel current-sensitive X-ray measurement device, called a VIEC. The VIEC employed a charge-sensitive preamplifier, which had low noise characteristics, and measured operating time between two successive resets of feed-back capacitance of the charge-sensitive preamplifier. The measured electric current by the VIEC showed a good linear relationship with the one measured by a commercial dose rate meter. (author)

[en] To investigate the shielding effects of full-face mask respirators and the suitable positioning of lens dosemeters, irradiation experiments of ⁹⁰Sr+⁹⁰Y beta particles were performed using an anthropomorphic head phantom into the eyes of which small thermoluminescence dosemeters (TLDs) were loaded, and the lens doses measured by these TLDs were compared with the doses measured by commercially available personal dosemeters attached around the eyes of the phantom. The three tested masks reduced the beta lens dose to 9-14% as compared to the lens doses in the absence of a mask. As for the suitable positioning of lens dosemeters, the H_p(0.07) evaluated by the H_p(0.07) dosemeter attached at the center of the forehead gave an over-response to the lens dose by a factor of 2.5-8.4 regardless of the presence of masks. The H_p(3) evaluated by the H_p(3) dosemeters, even though placed at extreme positions near the outside corners of the eyes, provided better lens dose estimates with a response of 0.38-1.7, which suggests the potential for improved results when H_p(3) dosemeters are placed at the center of the forehead. (author)

[en] It is commonly believed that when electron beams with energy of more than MeV scale are irradiated to water, a Cerenkov-ring is formed and observed in the forward direction of the beam. We tried to observe the Cerenkov-ring in water during irradiation of high-energy electrons or X-ray beams. We irradiated 1-cm-diameter electron beams to water with energy of 6 to 12 MeV from a linear accelerator (LINAC), and then we imaged the produced light with a translucent plate in water at the forward position. We also irradiated 0.5 x 0.5-cm 6-MV and 10-MV X-rays to water, and imaging was conducted with the same set-up. For all electron energies, the formed images did not have any ring shape but only a round shape with highest intensity at the center of the circles. Monte Carlo simulation also showed that no ring formed and that the distributions were similar to those of the experimental results. For X-ray irradiation, high intensity spots were observed at the center of the image, and no ring shape was observed. Our results indicate that electrons or X-ray beams do not produce any Cerenkov-ring in the forward direction with the beam energies we used for the experiments. This is because the scattered electrons produced Cerenkov-light not only in the forward direction but also in many directions, which made it impossible to observe the ring shape, in addition to the effect of the water’s luminescence having lower energy than the Cerenkov-light threshold. (author)

[en] The workshop was hosted by Radiation Science Center at Applied Research Laboratory (ARL), KEK under the cooperation of the Society of Radiation Science, the affiliate of Japan Society of Applied Physics. In this workshop, there were more than 70 participants, and 23 presentations were given. As the fruits of this workshop, this report is published. All papers submitted for publication received the peer review process by the independent reviewers. Finally, 10 original papers were published in the proceedings. This issue is the collection of the paper presented at the title meeting. The 10 of the presented papers are indexed individually. (J.P.N.)