| abstract |
(57) Abstract: Provided is an ionization chamber detector in which a self-contamination dose rate by an aluminum outer electrode and an aluminum cover does not exceed a predetermined value of 10 nGy / h or less without forming a shielding film. Assuming that a predetermined value of a self-contamination dose rate is SnGy / h, a material aluminum used for an outer electrode and a cover is made of a material having a count number of β-rays emitted from the material aluminum of 80S count / 10h or less, or This material in aluminum Concentrations of 238 U and 232 Th, 39 K are 1 ppm of 238 U 1.05 units, 232 Th 1 ppm 0.30 units, 1 ppm of 39 K Is 3.0 × 10 -5 units, and the material is limited to materials of 0.25 S units or less in total of three nuclides. |