PROBLEM TO BE SOLVED: To highly accurately measure a distribution of dose of radiation beams.SOLUTION: A holder 108 holds a plurality of parallel plate ionization chambers 104 in a stacked state. The holder 108 has a spacer 120 for forming a space between the parallel plate ionization chambers 104. The parallel plate ionization chamber 104 has an ionization chamber case 201 internally forming an ionization chamber cavity 202 and an ionization chamber electrode 203 formed on an inner surface of the ionization chamber case 201 in contact with the ionization chamber cavity 202. The ionization chamber electrode 203 has a signal electrode 203a to which a signal is inputted, and a high-voltage electrode 203b to which a high potential is inputted, and the plurality of parallel plate ionization chambers and the holder are disposed in water 103.COPYRIGHT: (C)2012,JPO&INPIT【課題】放射線ビームの線量分布測定を高精度に行うことを目的とする。【解決手段】平行平板電離箱104の複数を積層状に保持するホルダー108を備え、ホルダー108は、平行平板電離箱104のそれぞれの間に空間を形成するスペーサ120を有し、平行平板電離箱104は、その内部に電離箱空洞202を形成する電離箱ケース201と、電離箱空洞202に接する電離箱ケース201の内面に形成された電離箱電極203とを有し、電離箱電極203は、信号が入力される信号電極203aと高圧電位が入力される高圧電極203bを有し、これらの複数の平行平板電離箱とホルダーは水103中に配置される。【選択図】図1
