1mg²⁵²Cf中性子源による熱中性子ラジオグラフィ

抄録

A transportable exposure device equipped with a 1-mg²⁵²Cf neutron source was designed and constructed for thermal neutron radiography. It has three divergent collimators with a large outlet aperture of 200 mm in diameter. These collimators have the same length (L) of 500 mm and an inlet aperture (D) of different sizes; 10, 20 or 40 mm in diameter. A thermal neutron flux of 3.0×10³cm^-2·s^-1 was obtained at the outlet of the collimator for L/D ratio of 25. The ratio of thermal neutron flux to γ-ray dose rate was 2.9×10⁴cm^-2·mR^-1 at the same position. It was shown that direct exposure method using the combination of a scintillation converter (NE-426) and a fine-grain film (Kodak-SR) is an appropriate choice for high quality radiographs. The method was effectively applied to detect hydrogen in some kinds of metal plate. The lower limit of detection for Al plates less than 10 mm thick was 0.64 mg·H·cm^-2. Track-etching method using an enriched-¹⁰B converter in contact with a nitrocellulose film was also found to show an excellent image resolution in such low flux neutron imaging under high γ-ray background.