Measurement of Smith-Purcell Radiation Spectrum from a Photonic Crystal(III. Accelerator, Synchrotron Radiation, and Instrumentation)

フォトニック結晶の表面近傍を高エネルギー (150MeV) の電子ビームが等速度で通過する時に, ミリ波領域の光放射が観測される。この光は, 電子から放射されたエバネッセント波 (減衰波) が進行波に変換されたものであり, フォトニックバンドモードを共鳴的に励起した際に放出される光であることがわかった。しかしそのメカニズムに対応しない放射ピークが出現したため, この光放射起源を特定するための実験を行った。また, 2層の3次元フォトニック結晶を用いて放射強度を増幅させることに成功した。When the electron beam of high energy (150MeV) passes near the surface of a photonic crystal at uniform velocity, optical radiation in a millimeter wave region is observed. It turns out that this light is converted from the evanescent wave emitted by the electrons into propagating waves through the photonic band modes in resonance. Since the previous measurements showed that a radiation peak appeared in out of region above the mechanism, the experiments for specifying the origin of this radiation was conducted. It was observed that intensity of the radiation increased for a 3D photonic crystal of double layers

Assessment of Instructions on Protection Against Food Contaminated with Radiocesium in Japan in 2011

The Japan Ministry of Health, Labour and Welfare (MHLW) has published instructions for radiological protection against food after the Fukushima Daiichi nuclear power plant accident in 2011. Following the instructions, the export and consumption of food items identified as being contaminated were restricted for a certain period. We assessed the validity of the imposed restriction periods for two representative vegetables (spinach and cabbage) grown in Fukushima Prefecture from two perspectives: effectiveness for reducing dietary dose and economic efficiency. To assess effectiveness, we estimated the restriction period required to maintain consumers\u27 dose below the guidance dose levels. To assess economic efficiency, we estimated the restriction period that maximizes the net benefit to taxpayers. All estimated restriction periods were shorter than the actual restriction periods imposed on spinach and cabbage from Fukushima in 2011, which indicates that the food restriction effectively maintained consumers\u27 dietary dose below the guidance dose level, but in an economically inefficient manner. We also evaluated the response of the restriction period to the sample size for each weekly food safety test and the instructions for when to remove the restriction. Stringent MHLW instructions seemed to sufficiently reduce consumers\u27 health risk even when the sample size for the weekly food safety test was small, but tended to increase the economic cost to taxpayers

Observation of Smith-Purcell Radiation and Unknown Radiation from a Photonic Crystal(III. Accelerator, Synchrotron Radiation, and Instrumentation)

フォトニック結晶から放射されるスミス・パーセル放射 (SPR) と従来の理論では説明できない放射の起源を明らかにすべく, 周期構造, 端面構造, 層数の異なるサンプルについて放射を観測した。理論計算との比較から正規のスミス・パーセル放射, 未解明放射ともにフォトニックバンド上にあることがわかった。層数を増やすと未解明放射が増強することから, 内部で特定のフォトニックバンドモードが励起されて放射されていると考えられる。The normal and unknown Smith-Purcell radiation (SPR) from samples that were different in periods, edge structure, and number of layer has been studied. Comparing with theoretical calculation of photonic bands, it has been found that unknown radiation as well as SPR lies on the photonic bands. The intensity of unknown radiation is enhanced by increase of the number of sample layer. Therefore, this unknown radiation may be emissions from excited photonic band modes in the photonic crystal