An optimized method for neutron dose evaluation based on²⁴Na activity distribution in the human body

Area of Science:

• Medical Physics
• Radiation Detection and Measurement
• Nuclear Engineering

Background:

• External neutron dose evaluation relies on measuring characteristic gamma rays from sodium-24 (24Na) in the human body.
• Optimal detection geometries for whole-body 24Na activity measurement remain understudied, impacting dose assessment accuracy.

Purpose of the Study:

• To investigate optimal detection geometries for measuring whole-body 24Na activity.
• To calculate the spatial distribution of 24Na and gamma ray fluence in the human body under various neutron irradiation conditions.
• To develop a practical method for accurate neutron dose assessment from continuous energy spectrum neutrons.

Main Methods:

• Utilized MCNP code to simulate 24Na spatial distribution and gamma ray fluence for neutrons of varying energies and irradiation geometries.
• Simulated 24Na characteristic gamma ray counts from monochromatic neutron irradiation to model continuous energy spectrum scenarios.
• Calculated atom production for a 1 Gy dose from 252Cf neutrons and determined detection limits.

Main Results:

• Identified optimal detector placement over the human back near the liver, reducing the lower detection limit for neutron absorption dose to below 1 mGy.
• Achieved less than 5.7% relative error when fitting 252Cf neutron irradiation data with monochromatic neutron irradiation data.
• Demonstrated that (3.63-4.35) × 10^10 24Na atoms are produced by a 1 Gy dose from 252Cf neutrons.

Conclusions:

• The study provides an optimized detection geometry for enhanced sensitivity in neutron dose assessment.
• A practical method for rapid and accurate neutron dose determination using weighted summation of monochromatic irradiation data is established.
• This approach offers a more convenient and practical alternative to previous methods for evaluating neutron dose from continuous energy spectrum sources.