T. Miura

Radiation hardness of cerium-doped gadolinium silicate Gd2SiO5:Ce against high energy protons, fast and thermal neutrons

Abstract Degradation of Gd 2 SiO 5 :Ce in optical transmittance due to proton irradiation was negligibly small below 10 6 rad, smaller than 2%/cm at 10 7 rad and large at 10 8 rad. The radiation hardness of 10 7 rad against protons is by two orders of magnitude smaller than against low energy γ-rays. Long term spontaneous recovery of the proton-induced damage is not large (10–20% of the initial degradation in 84 days). Recovery upon exposure to UV light occurs to some extent. Degradation due to thermal neutrons was negligibly small for a fluence of 10 14 n/cm 2 . No degradation was observed for exposure to fast neutrons of about 10 13 n/cm 2 during one year in the extracted beam tunnel of proton synchrotron.

Radiation hardness of undoped CsI crystals against high energy protons

Abstract We compared radiation damages of undoped CsI for 12 GeV protons and for 60Co γ-rays between 104 and 108 rad. Degradation in optical transmission was similar in magnitude both for protons and γ-rays; it is as small as 1–3% per 1 cm thickness at 104 rad, while it is as large as or larger than 5% above 105 rad. The above feature is different for BGO or GSO:Ce, whose radiation hardness is roughly two orders of magnitude smaller regarding protons than regarding γ-rays. Recovery of damage is qualitatively similar both for proton and γ-ray irradiations; spontaneous recovery is only partial and the annealing effect of UV exposure is negligibly small.

AMS analysis of 36Cl induced in concrete of accelerator facilities

Accelerator mass spectrometry (AMS) was applied to the analysis of 36Cl induced in concrete samples obtained from accelerator facilities. In order to use a small amount of concrete sample and to separate chlorine as pure as possible, an improvement of separation process was developped. Chlorine was extracted from 1–5 g of concrete into 0.01 M nitric acid in a pressurized decomposition vessel. After determining chlorine using ion chromatography, a certain amount of NaCl solution was added to obtain sufficient amounts of AgCl precipitate and to dilute to a suitable isotope ratio of 36Cl to 35Cl (36Cl/35Cl) for the AMS (10-12–10-10). A careful purification procedure was applied to reduce 36S interference in AMS. Good reproducibility and small error throughout the chemical process for sample preparation was attained. Depth profiles of 36Cl/35Cl in concrete of a medium-energy cyclotron were measured by the developed method and compared with the results of γ-emitters induced by thermal neutrons. Since it was confirmed that 36Cl was produced by thermal neutron capture of 35Cl, the thermal neutron fluence irradiated during accelerator operation could be obtained using 36Cl/35Cl. In order to estimate the neutron fluences, the 36Cl/35Cl measurement by AMS is more useful than radioactivity measurements of other isotopes such as γ-emitters because AMS directly provides the isotope ratio and the half-life of 36Cl is very long.

Muon capture probability of carbon and oxygen for CO, CO2, and COS under low-pressure gas conditions

When a negatively charged muon is stopped in a substance, it is captured by an atom of the substance, and the muonic atom is formed. The muon capture process is significantly affected by the chemical environment of the atom and factors such as molecular structure (chemical effect). In this study, we performed muon irradiation for low-pressure CO, CO2, and COS molecules and measured the muonic X-rays emitted immediately after muon capture by an atom. In this paper, we quantitatively discuss the muon capture probability of each type of atom using the LMM model.

Migration of radionuclides induced in the soil below the 12 GeV proton accelerator facility at KEK

The radioactive concentrations of radionuclides were measured in the soil and groundwater below the 12 GeV proton beam-line tunnel at KEK. Various long-lived radionuclides, (7Be, 22Na, 46Sc, 54Mn, 60Co, 134Cs, 152Eu and 154Eu) were observed in the soil samples by γ-ray spectra measurements, and 3H was also detected by liquid scintillation counting. On the other hand, 3H, 22Na and 54Mn, which were leached from the soil were measured in the groundwater below the EP2 beam line. 3H and 22Na were also found in slight amounts in groundwater collected in a well dug beside the East Counter Hall. From a comparison with the radioactive concentration in soil and groundwater, the order of the leaching percentages were 3H>22Na>54Mn. This tendency was in agreement with an experimental result of the RI laboratory.

Behavior of pionic hydrogen atoms in liquid organic compounds

Negative pion transfer from pionic hydrogen to other heavier atoms was studied in some liquid organic compounds. The pion capture probability on hydrogen at a particular site in the molecules was obtained using deuterated compounds for alcohols and carboxylic acids. The transfer process to carbon atoms in different chemical states was also studied in the mixtures of C6 H12 or C6 H6+ CCl4. These methods revealed that the pionic hydrogen atoms originating from hydrogen in different chemical environments showed different behavior. The transfer process was discussed using a large mesomolecular model combined with an external transfer process.

Negative pion transfer process in a hydrogen-containing gas mixture

Annihilation γ-rays of π0 and pionic X-rays were measured in the gas mixtures of H2+Z and CH4+Z systems (Z=He, Ne, Ar and Kr). Pion capture probability of hydrogen atom was obtained from the annihilation γ-ray counts and the capture probability of Z atom was obtained from the pionic X-ray intensities. Transfer rates were determined from the data based on a combined large mesomolecular model. The transfer rates obtained were smaller than the systematics of the Russian group. Difference in the transfer rate between the gas and the liquid phases was found by a comparison of the present results with our previous ones.

Aerosol-size distribution of radon daughter218Po in the accelerator tunnel air

Aerosol-size distributions of218Po were determined for the accelerator tunnel air sampled during machine operation and for the basement air of a concrete building, where the number and the size distribution of non-radioactive aerosols are greatly different from each other. The218Po distributions depended very much on the size distributions of ambient non-radioactive aerosols, and could be well explained by an attachment model of218Po to ambient non-radioactive aerosols.

Particle size and fuming rate of radioactive aerosols generated during the heat cutting of activated metals

Abstract The particle sizes and fuming rates of radioactive nuclides and matrix elements were extensively investigated for aerosols generated by the heat cutting of activated metals. The aerosols showed either lognormal activity or mass distributions with modes at 0.3∼0.5 μm and/or 4∼6 μm. Some carrier-free radioactive nuclides were remarkably enriched in the aerosols, and showed different distribution patterns from matrix metal elements. The results are discussed on the basis of the thermal properties of the radioactive and matrix elements.

Energy shift of electronic X-rays emitted from pionic atoms

Summary The electronic K X-ray energies of pionic atoms were precisely measured on elements ranging from zinc to lead with a low-energy photon detection system. Some differences between pionic and muonic atoms were found in the atomic-number (Z) dependence of the energy shift. In the pionic atoms, the energy shift gradually decreases with an increase in atomic number, which is opposite to the trend for muonic atoms. In the low-Z region investigated elements, the energy shifts of Kβ X-rays were obviously larger than those of Kα X-rays.