Study on the ²⁴Na specific activity induced by external neutron irradiation based on ICRP 110 computational phantoms

The dose caused by external exposure to neutrons can be evaluated by measuring the induced ²⁴Na activity due to interaction of ²³Na in human body with neutrons. To investigate the difference between male and female in the ²⁴Na activity, the MCNP code is used to simulate the ICRP 110 adult male and female reference computational phantoms irradiated by ²⁵²Cf neutrons. The results show that the average absorbed dose of whole body caused by per unit neutron fluence for the female phantom is (5.22 ± 0.06)% - (6.84 ± 0.05)% higher than that for the male phantom. The ²⁴Na specific activity of male tissues/organs is higher than that of female, except muscle tissues, bone, colon, kidney, red marrow, spleen, gallbladder, rectum and gonads. The highest intensity of ²⁴Na characteristic gamma rays on the body surface occurred at Z = 125 cm on the back for the male phantom, while the highest gamma ray fluence for the female phantom is at Z = 116 cm, both of which are aligned with liver. When 1 Gy of ²⁵²Cf neutrons irradiate the ICRP110 phantoms, (1.51-2.44) × 10⁵ and (3.70-5.97) × 10^{4 24}Na characteristic gamma rays can be recorded in 10 min by 3-inch NaI(Tl) detector and Φ 5 × 3 cm³ HPGe detector, respectively.