抄録
High energy γ-ray irradiation field for calibrating radiation measuring instruments has been established.
16N, whose half life is very short (7.13sec), emitts 6.129MeV and 7.115MeV γ-rays in relative intensity 69% and 4.8%, respectively. 16N is formed by the reaction 16O(n, p)16N in cooling water of reactor. The primary cooling water in JRR-4, JAERI, can be pumped and circulated in a small closed loop continuously, and some part of the loop passes outside the biological shield of the reactor and acts as a 16N source. Exposure rate at 1m from the 16N source is 7.1mR/h when the water flow rate of the loop is 35l/min and the power of JRR-4 is 3.5MW.
The influence on the 16N γ-ray exposure rate by the contamination of electrons can be lowered significantly by covering the 16N source with such as methacrylic resin of thickness 2g/cm2 or more. The influences on the 16N γ-ray exposure rate by annihilation γ-rays, 24Na γ-rays and scattered γ-rays are 1.67%, 1.35% and 15% respectively at 3m from the 16N source.
