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Absolute Calibration of Radioactive Neutron Source Strength by Geometrical Integration of Thermal Neutrons in Graphite Pile

Absolute calibrations of radioactive neutron source strength Q n/s have so far been conventionally carried out by means of the so-called water-bath or MnSO4-bath technique using a water moderator. Here, we present the method and results of a new technique for the absolute calibration of Q by elaborately integrating the spatial distributions of thermal neutron flux inside and on the surface of the high-purity graphite moderator with dimension of 2.5 ×1.9 ×1.9 m3. The combined standard uncertainty for absolute Q obtained from the presented technique was ±2.0%, which is comparable to those of the conventional methods.