NAA and low-background Υ- spectrometry for the analysis of U and Th in high purity silica used in electronic devices

It has been established that soft error of high precision electronic circuits can be induced by alpha particle emitted from the naturally occurring radioactive impurities such as U and Th. Silica has used in electronic industries as the base materials and impurities must be controlled strictly. Recently, electronic circuits have become lower dimension and higher density, so alpha-particle emitting radioactive impurities have to be strictly controlled. The objective of the present study was to develop of NAA and gamma-spectrometry for the sensitive (ng/g) and precise analysis of U and Th. A new NAA method has been established using the HTS irradiation facility which has been used to produce radioisotopes for industries and medicines. When the ultratrace impurities have to be analyzed by NAA, background gamma-ray spectra induced from 222Rn and its progeny nuclides in atmosphere are serious problem. This unstable background was eliminated and stabilized by the use of a nitrogen purging system. By the use of HTS-NAA and low background gamma-spectrometry ultratrace amounts of U (0.1ng/g) and Th (0.01ng/g) in high purity silica could be analyzed