Shape distortion of 128I ß spectrum observed by a self-activated CsI(Tl) scintillator for high-sensitivity neutron measurements

Soichiro Honda, Akihiro Nohtomi, Keita Machidori, Genichiro Wakabayashi

研究成果: Contribution to journalArticle

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The factors causing the distortion of the 128I ß spectrum detected by a self-activated CsI(Tl) scintillator were studied to verify the correctness of the spectral shape and the appropriateness of the discrimination setting for ß-particle counting by the scintillator. These criteria are essential for the correct evaluation of radioactivity generated in a scintillator volume by the self-activation method, which was recently proposed by our group. A pulse height defect caused by the partial escape of ß particles from the surface of the scintillator crystal shifts the ß spectrum toward the lower-energy region when smaller CsI(Tl) scintillators are used (the ß-escape effect). For larger CsI(Tl) scintillators, an increase in pulse height caused by the summing of 0.443 MeV prompt γ-rays from the excited state of the 128I daughter nuclide (128Xe) affects the shape of the ß spectrum considerably, resulting in a shift toward the higher-energy region (the γ-summing effect). The extent of the contributions of these two effects was examined by a Monte Carlo simulation of various cubical CsI(Tl) crystals of different sizes. It was found that the distortions caused by those two effects effectively cancel each other out for a medium-size cubical CsI(Tl) crystal with a side length of approximately 3 cm. This finding is very useful for the practical applications of the self-activation method. In addition to the factors mentioned above, the efficiency of scintillation light collection by the photodetectors also affects the shape distortion of the ß spectrum slightly through spectral line broadening due to the degradation of the energy resolution. This effect was estimated using a simple model with different discrimination settings for ß pulse counting.

ジャーナルNuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
出版物ステータス出版済み - 11 1 2017

All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics
  • Instrumentation

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