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) × 104 24Na characteristic gamma rays can be recorded in 10 min by 3-inch NaI(Tl) detector and Φ 5 × 3 cm3 HPGe detector, respectively.