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菊地暁・佐藤守弘編『学校で地域を紡ぐ --『北白川こども風土記』から--』, Special Book Review : A. Kikuchi & M. Sato eds. Weaving Regions in Schools : From Kitashirakawa Kodomo Fudoki, (2020)

第8回極域科学シンポジウム/個別セッション：[OG] 極域地圏12月5日（火）国立極地研究所 3階セミナー室The Eighth Symposium on Polar Science/Ordinary sessions: [OG] Polar GeosciencesTue. 5 Dec./3F Seminar room, National Institute of Polar Research

Neutron double-differential cross sections from carbon ion incident on carbon, nitrogen and oxygen targets have been measured for neutron energies down to 0.6 MeV in wide directions from 15∘ to 90∘ with 100- and 290-MeV/A incident energies at the Heavy Ion Medical Accelerator in Chiba (HIMAC), National Institute of Radiological Sciences. Two sizes of NE213 scintillators were used as neutron detectors in order to enable neutron energy from below one to several hundred MeV. The neutron energy was measured by the time-of-flight technique between the beam pickup detector and an NE213 scintillator. By using the experimental data, the validity of the calculation results by the PHITS code was examined.

Angular distributions of absorbed dose of Bremsstrahlung photons and secondary electrons at a wide range of emission angles from 0 to 135, were experimentally obtained using an ion chamber with a 0.6 cm(3) air volume covered with or without a build-up cap. The Bremsstrahlung photons and electrons were produced by 18-, 28- and 38-MeV electron beams bombarding tungsten, copper, aluminium and carbon targets. The absorbed doses were also calculated from simulated photon and electron energy spectra by multiplying simulated response functions of the ion chambers, simulated with the MCNPX code. Calculated-to-experimental (C/E) dose ratios obtained are from 0.70 to 1.57 for high-Z targets of W and Cu, from 15 to 135 and the C/E range from 0.6 to 1.4 at 0; however, the values of C/E for low-Z targets of Al and C are from 0.5 to 1.8 from 0 to 135. Angular distributions at the forward angles decrease with increasing angles; on the other hand, the angular distributions at the backward angles depend on the target species. The dependences of absorbed doses on electron energy and target thickness were compared between the measured and simulated results. The attenuation profiles of absorbed doses of Bremsstrahlung beams at 0, 30 and 135 were also measured.

Rapid measurement of radioactivity from 89,90Sr in aqueous solutions is performed using a technique combining a strontium rad disk and a picobeta spectrometer. Identification of 89,90sr radionuclides is accomplished in as little as 90min in a radiation-tainted solution that contains more highly radioactive cesium. It is possible to perform triage by assessing skin exposure doses in this short time. This simple technique could be used in mobile laboratories. 89,90Sr having 1 Bq radioactivities are measured in 10 kBq 137Cs in aqueous solution. The radioactivity contained in rinse water used to decontaminate the feet of workers who stepped into highly contaminated water in the basement of the turbine building of Unit 3 at the Fukushima Daiichi nuclear power station was measured. The amount of 90Sr radioactivity in rinse water using the authors'rapid measurement technique (0.29Bq mL-1)and a traditional method agree well, with 3.6% difference. Based on this agreement, this technique is confirmed to be useful for rapid measurement of 89,90Sr radioactivities.

Using a high-purity germanium detector, both indoor and outdoor radionuclides that had deposited 1.5 d after the radioactive fallout events in the city of Fukushima were experimentally measured. Eleven artificial (131I, 132I, 134Cs, 136Cs, 137Cs, 129Te, 129mTe, 131mTe, 132Te, 140La and 99mTc) and 5 natural radionuclides were identified. Total air kerma rates were mainly due to 132I, 134Cs and 136Cs from 4 to 6uGy/h at a 7.5-cm height from the ground. Radioactive contamination on the ground was contributed by 132I and 132Te, from 330 to 420 Bq/cm2. In a worst-case scenario, the maximum skin dose rates were estimated to be from 520 to 670 uGy/h. Effective dose rates were evaluated to be 10 to 15 uSv/h and reached 17.9 uSv/h at 4 a.m.on 16 March. In the effective dose rates, 132I, 134Cs and 132Te were the main contributors. Our measurements are useful for estimating dose levels in the public in the city of Fukushima during the days after radioactive fallout contamination.

Angular distributions of absorbed dose of Bremsstrahlung photons and secondary electrons at a wide range of emission angles from 0 to 135, were experimentally obtained using an ion chamber with a 0.6 cm3 air volume covered with or without a build-up cap. The Bremsstrahlung photons and electrons were produced by 18-, 28- and 38-MeV electron beams bombarding tungsten, copper, aluminium and carbon targets. The absorbed doses were also calculated from simulated photon and electron energy spectra by multiplying simulated response functions of the ion chambers, simulated with the MCNPX code. Calculated-to-experimental (C/E) dose ratios obtained are from 0.70 to 1.57 for high-Z targets of W and Cu, from 15 to 135 and the C/E range from 0.6 to 1.4at 0: however, the values of C/E for low-Z targets of Al and C are from 0.5 to 1.8 from 0 to 135 . Angular distributions at the forward angles decrease with increasing angles; on the other hand, the angular distributions at the backward angles depend on the target species. The dependences of absorbed doses on electron energy and target thickness were compared between the measured and simulated results. The attenuation profiles of absorbed doses of Bremsstrahlung beams at 0, 30 and 135 were also measured.

We developed a real-time and non-destructive method of beam profile measurement on a target under large beam current irradiation, and without any complex radiation detectors or electrical circuits. We measured the beam profiles on a target by observing the target temperature using an infrared-radiation thermometer camera. The target temperatures were increased and decreased quickly by starting and stopping the beam irradiation within 1 s in response speed. Our method could trace beam movements rapidly. The beam size and positiun were calibrated by measuring O-ring heat on the target. Our method has the potential to measure beam profiles at beam current over 1 mA for proton and deuteron with the energy around 3Mev and allows accelerator operators to adjust the beam location during beam irradiation experiments without decreaseing the beam current.

The double-differential cross sections (DDXs) for the inclusive reactions producing heavy nuclei with Z ¼ 2–9 (fragments) from carbon, aluminum, and silicon targets induced by 50 and 70 MeV protons are systematically measured at several angles (308, 608, 908, and 1358) using a specially developed Bragg curve counter and the energy-time-of-flight method. The DDXs of a silicon target for the proton-induced reaction producing fragments heavier than lithium were measured for the first time. The present results are compared with past experimental data, the LA150 evaluated data by the Los Alamos group and several intranuclear cascade models (Bertini and ISOBAR), and the JAEA-version quantum molecular dynamics model (JQMD) coupled with the Generalized Evaporation Model (GEM), which are implemented in the Particle and Heavy Ion Transport code System (PHITS). The present results agree well with the past experimental data and LA150 data for a -particle production. For the fragments heavier than lithium, the present results show forward-peak angular distributions rather than isotropic ones stored in LA150. Calculations with the ISOBAR and GEM models well reproduced our experimental results except for light fragments especially in the high-energy region.

The frequency distributions of the lineal energy, y, of 160 MeV proton, 150 MeV/u helium, and 490 MeV/u silicon ion beams were measured using a wall-less tissue equivalent proportional counter (TEPC) with a site size of 0.72 um. The measured frequency distributions of y as well as the dose-mean values, , agree with the corresponding data calculated using the microdosimetric function of the particle and heavy ion transport code system PHITS. The values of increase in the range of LET below ~10 keV um–1 because of discrete energy deposition by delta rays, while the relation is reversed above ~10 keV um–1 as the amount of energy escaping via delta rays increases. These results indicate that care should be taken with the difference between and LET when estimating the ionization density that usually relates to relative biological effectiveness (RBE) of energetic heavy ions.

Cosmic-ray neutron energy spectra from thermal to 15 MeV were measured with the multi-moderator spectrometer known as the Bonner Ball Neutron Detector (BBND) at aviation altitude (9-11 km). Four flights were carried out around the Nagoya Airport in Japan. The measured data were unfolded using the maximum entropy deconvolution code MAXED, and the derived spectra agreed with calculated results using the PHITS-based Analytical Radiation Model in the Atmosphere (PARMA). The results of the in-flight measurement verified the accuracy of model calculation in regard to the neutrons within a certain energy range.

To improve radiation safety in high-energy accelerator facilities, the authors have been developing the new radiation dose monitor device DARWIN: Dose monitoring system Applicable to various Radiations with WIde energy raNges. DARWIN is composed of (a) a phoswitch-type scintillation detector, which consists of liquid organic scintillator BC501A coupled with ZnS(Ag) scintillation sheets doped with 6Li, and (b) a data acquisition (DAQ) system for digital analysis of the waveform of the scintillator signals. The DAQ system was recently updated in order to apply DARWIN in monitoring dose rates in radiation fields having time structure, introducing an originally developed module based on a field-programmable gate array. To examine the performance of DARWIN placed in radiation fields composed of varieties of particles over wide energy ranges, the authors mounted DARWIN on a jet aircraft and measured neutron, photon, muon, electron, and positron dose rates at high altitudes. The measured dose rates excellently agreed with the corresponding data calculated by EXPACS over a wide altitude range. This agreement indicates the applicability of DARWIN to dose monitoring in complex radiation fields such as those in high-energy accelerator facilities and aircrafts.

Previously published data of secondary neutron spectra from thick targets of C, Al, Cu and Pb bombarded with heavy ions from He to Xe are revised by using a new set of neutron-detection efficiency values for a liquid organic scintillator calculated with SCINFUL-QMD. Additional data have been measured for bombardment of C target by 400-MeV/nucleon C ions and 800-MeV/nucleon Si ions. The set of spectra are compared with the calculation results using a Monte-Carlo heavy-ion transport code, PHITS. It was found that PHITS is able to reproduce the secondary neutron spectra in a wide neutron-energy regime.

Absorbed doses from main charged-particle beams and charged-particle fragments have been measured with high accuracy for particle therapy, but there are few reports for doses from neutron components produced as fragments. This study describes the measurements on neutron doses produced by carbon beams; microdosimetric distributions of secondary neutrons produced by 290 MeV/nucleon carbon beams have been measured by using a tissue equivalent proportional counter at the Heavy Ion Medical Accelerator in Chiba, Japan at the National Institute of Radiological Sciences. The microdosimetric distributions of the secondary neutron were measured on the distal and lateral faces of a body-simulated acrylic phantom (300 mm heightx300 mm width x253 mm thickness). To confirm the dose measurements, the neutron energy spectra produced by incident carbon beams in the acrylic phantom were simulated by the particle and heavy ion transport code system. The absorbed doses obtained by multiplying the simulated neutron energy spectra with the kerma factor calculated by MCNPX agree with the corresponding experimental data fairly well. Downstream of the Bragg peak, the ratio of the neutron dose to the carbon dose at the Bragg peak was found to be a maximum of 1.4x10−4 and the ratio of neutron dose was a maximum of 3.0x10−7 at a lateral face of the acrylic phantom. The ratios of neutrons to charged particle fragments were 11% to 89% in the absorbed doses at the lateral and the distal faces of the acrylic phantom. We can conclude that the treatment dose will not induce serious secondary neutron effects at distances greater than 90 mm from the Bragg peak in carbon particle therapy.

A phoswich detector was developed to measure neutron energy spectra from a few MeV to a few hundreds MeV in aircrafts and space crafts. Radiation fields, which both crafts are exposured, consist of neutrons, gamma rays, protons, etc. The phoswich detector can measure neutrons separately from gamma rays and protons. The capability of particle discrimination was tested at HIMAC and was found to be excellent. Detector response functions to neutrons were simulated with the MCNPX code using the measured light outputs of charged particles and were measured with quasi-mono-energetic neutrons produced by the p-Li reaction at the NIRS cyclotron. Test flight measurements at high altitudes, 6.5 and 8.5 km, were performed above the middle part of Japan (cut-off rigidity, 12 GV).

Energy-differential cross sections of fragment (heavier than a-particle) production of carbon and aluminum were obtained with a specially designed Bragg curve spectrometer (BCS) and energy-time-of-flight method (E-TOF) for 70 MeV protons at 30-degree laboratory angle. The consistency of these two methods was confirmed by comparing Z=2 results each other. The energy differential cross sections of fragments for Z=3 and m=6, 7 are obtained by BCS and E-TOF, respectively. These results are compared with other experimental data, LA-150 evaluated nuclear data and QMD calculation results. The disagreements between present data and both results of evaluation and calculation show systematic trends.