arXiv subjects

Ryugo Hayano

Publications and source records attributed to Ryugo Hayano.

4 recordsLinked to original sources

arXiv2017

Comparison of the UNSCEAR isodose maps for annual external exposure in Fukushima with those obtained based on the airborne monitoring surveys

In 2016, UNSCEAR published an attachment to its Fukushima 2015 White Paper, entitled "Development of isodose maps representing annual external exposure in Japan as a function of time," in which the committee presented annual additional 1 mSv effective dose ab extra isodose lines for 1, 3, 5, 10, 30, 50 years after the accident, based on the soil deposition data of radionuclides within 100 km from FDNPP. Meanwhile, the median of the ratio, c, between the external effective dose rates and the ambient dose equivalent rates at 1 m above the ground obtained by the airborne monitoring has been established to be c~0.15. We here compare the UNSCEAR predictions with respect to estimates based on the airborne monitoring. Although both methods and data used in the two approaches are di erent, the resultant contours show relatively good agreement. However, to improve the accuracy of long-term annual effective isodose lines, feedback from continuous measurements such as airborne monitoring is important.

physics.med-ph↗

arXiv2017

Measurement of Individual Dose from External Exposure among All Citizens of Date City 5 to 51 Months after the Fukushima NPP Accident: Prediction of Lifetime Additional Dose and Evaluating the Effect of Decontamination on Individual Dose

In the first paper of this series, we showed that the ratio c of individual dose to ambient dose did not change with time in Date City, Fukushima Prefecture, after the Fukushima Daiichi Nuclear Power Plant accident. The purpose of the present paper, the second in a series, is to estimate the lifetime doses of the Date City residents, based on continuous glass badge monitoring data, extrapolated by means of the ambient-dose-rate reduction function obtained from the airborne monitoring data. As a result, we found that the mean additional lifetime dose of residents living in Date City is not expected to exceed 18 mSv. In addition, effects of decontamination on the reduction of individual doses were not evident. This method of combining individual doses and the ambient doses, as developed in this study, has made it possible to predict with reasonable certainty the lifetime doses of residents who continue to live in this radiologically contaminated area.

physics.med-ph↗

arXiv2016

Individual External Dose Monitoring of All Citizens of Date City by Passive Dosimeter 5 to 51 Months After the Fukushima NPP Accident (series): 1. Comparison of Individual Dose with Ambient Dose Rate Monitored by Aircraft Surveys

Date City in Fukushima Prefecture has conducted a population-wide individual dose monitoring program after the Fukushima Daiichi Nuclear Power Plant Accident, which provides a unique and comprehensive data set of the individual doses of citizens. The purpose of this paper, the first in the series, is to establish a method for estimating effective doses based on the available ambient dose rate survey data. We thus examined the relationship between the individual external doses and the corresponding ambient doses assessed from airborne surveys. The results show that the individual doses were about 0.15 times the ambient doses, the coefficient of 0.15 being a factor of 4 smaller than the value employed by the Japanese government, throughout the period of the airborne surveys used. The method obtained in this study could aid in the prediction of individual doses in the early phase of future radiological accidents involving large-scale contamination.

physics.med-ph↗

arXiv2013

Two-photon laser spectroscopy of antiprotonic helium and the antiproton-to-electron mass ratio

Physical laws are believed to be invariant under the combined transformations of charge, parity and time reversal (CPT symmetry). This implies that an antimatter particle has exactly the same mass and absolute value of charge as its particle counterpart. Metastable antiprotonic helium ($\bar{p}{\rm He}^+$) is a three-body atom consisting of a normal helium nucleus, an electron in its ground state and an antiproton ($\bar{p}$) occupying a Rydberg state with high principal and angular momentum quantum numbers, respectively $n$ and $\ell$, such that $n\sim\ell\sim 38$. These atoms are amenable to precision laser spectroscopy, the results of which can in principle be used to determine the antiproton-to-electron mass ratio and to constrain the equality between the antiproton and proton charges and masses. Here we report two-photon spectroscopy of antiprotonic helium, in which $\bar{p}{\rm ^3He^+}$ and $\bar{p}{\rm ^4He^+}$ isotopes are irradiated by two counter-propagating laser beams. This excites nonlinear, two-photon transitions of the antiproton of the type $(n,\ell)\rightarrow (n-2,\ell-2)$ at deep-ultraviolet wavelengths ($λ$=139.8, 193.0 and 197.0nm), which partly cancel the Doppler broadening of the laser resonance caused by the thermal motion of the atoms. The resulting narrow spectral lines allowed us to measure three transition frequencies with fractional precisions of 2.3-5 parts in $10^9$. By comparing the results with three-body quantum electrodynamics calculations, we derived an antiproton-to-electron mass ratio of 1,836.1526736(23), where the parenthetical error represents one standard deviation. This agrees with the proton-to-electron value known to a similar precision.

physics.atom-ph↗