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To compare the response to high energy neutrons and protons of the space bubble detectors in use aboard the International Space Station (ISS), three series of experiments were conducted with high energy protons and neutrons. The first series of experiments was conducted with high-energy neutrons in the energy range expected for neutrons encountered during space flight (0.6–800 MeV) at the Los Alamos Neutron Science Center (LANSCE) using the spallation neutron source. The second series was conducted with high energy protons from 30 to 70 MeV using the cyclotron at the National Institute of Radiological Science NIRS in Japan, and the third series of experiments was performed with high energy protons from 60 to 230 MeV at the ProCure proton therapy facility, Oklahoma, USA. The bubble detectors were exposed to different fluences in different experiments and the number of bubbles was counted using a bubble detector reader. The proton response of the bubble detector (sensitivity), as a function of energy, was determined and compared to the neutron sensitivity. In addition, to adjust the neutron sensitivity of the bubble detector determined in an AmBe field, a calibration factor was obtained for space applications.

The fast neutron fields generated by accelerator-based neutron sources (ABNS) are generally results contamination of thermal neutrons and gamma rays. Therefore, discrimination techniques of these radiation effects are required for biological effect experiment in fast neutrons. Additionally, since interactions of neutrons strongly depend on its energy and detector materials, evaluations of neutron fields using absorbed dose of tissue equivalent due to neutron interactions are difficult. Therefore, it is necessary to define parameters for characterizations of fast neutrons and gamma rays in the neutron fields. We propose that radiation chemical yields of hydroxyl radicals (OH*) measured by coumarin-3-carboxylic acid (3CCA) aqueous solutions are used for the parameters. Moreover, the discrimination technique of these radiations for fluorescence intensities of 7OH-3CCA in the 3CCA aqueous solutions was developed. This work demonstrated utilities of the discrimination technique, and OH* generated by these radiations., 14th Tihany Symposium on Radiation Chemistry

We proposed a depth-intensity curve discrimination (DCD) method for assessing absorbed dose contributions of hydroxyl radicals (HO·) due to thermal neutrons, fast neutrons, and gamma rays in accelerator-based mixedradiation fields, that are relevant to boron neutron capture therapy (BNCT). The HO· yields of thermal neutrons, fast neutrons, and gamma-rays measured by coumarin-3-carboxylic acid solutions were discriminately evaluated using depth-intensity curves of their radiations and maximum likelihood-expectation maximization algorithm. The discrimination accuracies of the three types of radiation were 2.8%, 4.2%, and 1.0%, respectively. We demonstrated that the DCD method is appropriate to determine absorbed dose contributions of HO· in complex accelerator-based neutron fields for BNCT.

The Japanese lunar explorer SELENE was launched from Tanegashima Space Center on September 14, 2007. It consists of a main orbiter KAGUYA at 100 km altitude and two daughter satellites (relay satellite OKINA and VRAD satellite OUNA) with 14 scientific instruments. The high precision gamma-ray spectrometer (GRS) on KAGUYA measures 200 keV–12 MeV gamma rays to determine the elemental composition of the lunar surface. The GRS is composed of a large Ge crystal as a main detector and massive bismuth germinate (BGO) crystals and a plastic scintillator as anticoincidence detectors. The Ge detector is cooled by a Stirling cryocooler below 90 K during the observation. After successful launch of the spacecraft and initial checkouts, the GRS started the nominal observation on December 21, 2007, and the temperatures and counting rates of the GRS were confirmed to be stable. Energy spectra of gamma rays with a good energy resolution are being obtained over the lunar surface, which will allow us to make global maps of the elemental abundances of the Moon soon.

The origin of galactic cosmic rays (GCRs) nuclei is still unknown. Precise observation of ultra heavy GCRs would be an important step in resolving their origin including the remaining problems in cosmic ray astrophysics. A program to observe UH nuclei in GCRs is proposed which involves the use of a high performance solid-state track detector on board a long-duration balloon. The program focuses measuring the elemental and isotopic compositions of UH nuclei up to the actinides. The observation of nuclear composition covers a wide range of scientific themes including studies of nucleosynthesis in cosmic ray sources, chemical evolution of galactic material, the characteristic time of cosmic rays, and heating and acceleration mechanisms of cosmic ray particles.

The origin of Galactic Cosmic Rays (GCRs) nuclei is still unknown. The precise observation of ultra heavy nuclei (Z is greater than or equal to 30) in GCRs is important to resolve the problems remained in cosmic ray astrophysics. Observation program of these nuclei in GCRs is proposed with the use of high performance Solid-State Track Detector (SSTD) on board long-duration balloon or International Space Station (ISS). The program focuses to measure the isotopic abundance above iron-peak elements and the composition of the rare ultra heavy nuclei up to actinide elements with relativistic energy. The observation of their nuclear composition covers a wide range of scientific themes including studies of nucleosynthesis of cosmic ray sources, chemical evolution of galactic material, the characteristic time associated with cosmic rays, such as heating and acceleration mechanism of cosmic ray particles. In order to achieve the objectives, long-duration balloon and/or ISS capable of carrying very large scientific payloads for long extended period is thought as best suited. The possible approach is based on a large telescope array consisting of modularized SSTD stacks., 資料番号: AA0063706014

A possible mechanism for the formation of the source composition of cosmic rays is proposed by taking into account the condensation process occurring in the interstellar space. This process may have produced the overabundance of heavy and ultra heavy nuclei in the source composition as compared with the chemical composition of the sun. Since the chemical composition of galactic cosmic ray source is similar to that of meteorite as classified as C2, that of galactic cosmic rays was compared with that of silicon carbide of presolar grains. It is found that both the iron isotope ratios and chemical composition of ultra heavy cosmic rays are similar to those in presolar grains. The chemical composition of presolar grains and meteorites may give a clue to search for the birth place of cosmic rays in the interstellar space., 資料番号: AA0047898029

International Workshop on Advances in Cosmic Ray Science

International Workshop on Advances in Cosmic Ray Science

30th International Cosmic Ray Conference

30th International Cosmic Ray Conference