K. Iijima

Transformation of a system consisting of plane isotropic source and unit sphere detector into a system consisting of point isotropic source and plane detector in Monte Carlo radiation transport calculation

In a nuclear power plant accident, radioactive nuclides may be released which are distributed uniformly on the ground. If estimation of dose rate from such a source by a Monte Carlo calculation is attempted, some difficulty is encountered because the calculation efficiency is very low. To solve this low efficiency problem, we show that a plane isotropic source can be transformed into a point isotropic source by changing the detector shape from a unit sphere to a plane. We verified the validity of this transformation by the numerical comparison of unscattered photon fluence. As an example of this transformation, the ambient dose rate D i was calculated from the uniform radioactive nuclide distribution on the ground using the EGS5 Monte Carlo code. We also measured the radioactivity and ambient dose rate (M) on the KEK campus within a month after the releases from the Fukushima No. 1 Nuclear Power Plant accident. Using radioactivity data and D i, we calculated the ambient dose rate (C). The calculated and measured ambient dose rates agreed reasonably well; their ratio (C/M) was 0.62 to 1.28.

Ionization yields for heavy ions in gases as a function of energy

For the experimental determination of an average energy to produce an ion pair in gases, W, by heavy ions from accelerators an apparatus which consisted of an energy degrader, an ionization chamber, and a TOF system was designed and constructed, where two types of pulse operation modes in an ionization chamber were employed. Using this system the values of W were measured for He and C ions in pure argon and air as a function of energy of ions. For C ions the energy dependence of W was clearly observed, while W for He ions was approximately constant in a wide range of the energy. The values of W for He and for C ions obtained at the highest energies well agree with the values for alpha particles in each gas.

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.

W-values for heavy ions in gases

The determination of W, an average energy to produce an ion pair, for heavy ions in gases at atmospheric pressures has been made using heavy-ion beams from an accelerator. The values of W were measured for He²⁺ and C⁶⁺ (< 6 MeV/n) in propane-base tissue-equivalent gases of the pressures of 500 to 760 Torr as a function of the energy of ions. For C⁶⁺, the energy dependence of W was clearly observed, while W for He²⁺ was approximately constant over a wide range of the energy. The differential values of W (w) were also measured for C⁶⁺ (< 6 MeV/n and 100 MeV/n) and Ar¹⁸⁺ (100 MeV/n) and are almost equal to the value of W for He²⁺.

Energy dependence of W-values for heavy charged particles in gases

For determination of W, an average energy to produce an ion pair, in gases at atmospheric pressures for heavy ions, an apparatus consisting of a particle-energy degrader, an ionization chamber and a time-of-flight energy spectrometer was constructed, where two types of pulse operation modes in an ionization chamber were employed. Using heavy-ion beams from an accelerator, the values of W were measured for He2+, C6+, and N7+ ions in air and tissue-equivalent gas of the pressures of 500 to 760 Torr as a function of the energy of ions. For C6+ and N7 ions, the energy dependence of W was clearly observed in both gases, while W for He2+ ions was approximately constant over a wide rage of the energy. The differential W-values were also measured in two gases. In air, the differential W-values for C6+ and N7 ions are almost equal to the value of W for high energy electrons.

Average energy to produce an ion pair for heavy charged particles in gases measured as a function of particle energy

In order to determine W, an average energy to produce an ion pair, in gases at atmospheric pressures for heavy ions, an apparatus consisting of a particle-energy degrader, an ionization chamber and a time-of-flight energy spectrometer was constructed, where two types of pulse operation modes in an ionization chamber were employed. Using heavy-ion beams from an accelerator, the values of W were measured for He/sup 2+/, C/sup 6+/, and N/sup 7+/ ions in air and tissue-equivalent gas of the pressures of 500 to 760 torr as a function of the energy of ions. For C/sup 6+/ and N/sup 7+/ ions, the energy dependence of W was clearly observed in both gases, while W for He/sup 2+/ ions was approximately constant over a wide rage of the energy. The differential W-values were also measured in two gases. In air, the differential W-values for C/sup 6+/ and N/sup 7+/ ions are almost equal to the value of W for high energy electrons.

Average energy to produce an ion pair in gases for high energy heavy ions

The differential W-values, w, an average energy required to produce an ion pair, were measured for C6+, Ne10+ and Ar18+ with energies more than 100MeV/n from a heavy-ion accelerator in argon, air, and propane-base tissue-equivalent gas of the pressures more than 0.1MPa. The values of w are almost equal to those of W for He2+ in each gas, which are approximately constant over a wide range of the energy.