Analysis of radioactive impurities in alumina and silica used for electronic materials

It has been established that soft error of high precision electronic circuits can be induced by alpha-particles emitted from the naturally occurring radioactive impurities such as U, Th. As the electronic circuits have recently become lower dimension and higher density, these alpha-particle emitting radioactive impurities have to be strictly controlled. The aim of this study is to develop of NAA(Neutron Activation Analysis) and gamma-spectrometry to improve the analytical sensitivity(ng/g) and precision of U and Th. New NAA methods have been established using the HTS(Hydraulic Transfer System) irradiation facility which has been used to produce radioisotopes for industries and medicines instead of PTS(Pneumatic Transfer System) irradiation facility which has been used in general NAA. When the ultra-trace impurities have to be analyzed by NAA, background gamma-ray spectra induced from 222Rn and its progeny nuclides in air is serious problem. This unstable background has been eliminated or stabilized by the use of a nitrogen purging system. Ultra trace amounts of U(0.1ng/g) and Th(0.01ng/g) in alumina ball and high purity silica used for EMC could be analyzed by the use of HTS-NAA and low background gamma-spectrometry