水トリーの発生に伴う微弱X/γ線検出に関する一考察

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We have observed and reported that weak γ-ray was radiated from water treed samples. In order to study the influence of inorganic impurities such as metal ions in XLPE on the radioactivity, we measured X/γ-ray and neutron carefully from XLPE samples immersed in NaCl and/or Pb(CH3COO)2 solution using BF3, CdTe and NaI detector in the condition of low background radiation. The counting rate of CdTe detector increased linearly with that of NaI detector, but each counting rate was not proportional to the growth of water trees. Furthermore, definitive residual radiation in the water treed samples, which attenuated rapidly to background level within a few hours after beginning of measurement, was observed by a Ge detector. We consider that the γ-ray observed during and after HV applying was emitted from 214Pb and 214Bi, as a result of analysis of the energy spectra. It is, however, difficult to explain that atmospheric radon gas (222Rn) which decays to above isotopes accumulated abundantly in water treed samples, because HV was applied in an air-tight flask filled with the solution. On the whole, these phenomena on the radiation of X/γ-ray do not seem to be directly associated with the growth of water trees.