Distribution of spatial photoneutrons inside a 70 kg water phantom via neutron activation analysis

This study evaluated spatial Φth inside a 70 kg water phantom using the NAA method. Fifty indium foils were placed inside the water phantom and exposed under 15 MV LINAC for 2.5 min to yield the 10 Gy X-ray dose. The Φth value at the isocenter of the water was 1.03×106 n cm−2/Gy-X, and the maximum quantity of Φth appeared at the water surface along the z-axis, 3.99×106 n cm−2/Gy-X. The thermal neutron dose at isocenter of the water phantom occupied approximately 0.151% of the whole photo and neutron dose.