Multi-layer shielding optimization of a high activity ²⁴¹Am-Be mixed field irradiation facility

Area of Science:

• Nuclear Engineering
• Radiation Protection
• Materials Science

Background:

• Designing effective shielding for radioactive sources like americium-beryllium (Am-Be) is crucial for occupational safety.
• Previous neutron irradiation facility designs required optimization to meet stringent dose rate limits.
• Am-Be sources emit both neutrons and gamma rays, necessitating a comprehensive shielding strategy.

Purpose of the Study:

• To optimize neutron and gamma-ray shielding for a 30 Ci (1.11 TBq) Am-Be irradiation facility.
• To reduce the effective dose rate to below 10 μSv/h for occupationally exposed workers, adhering to ICRP recommendations.
• To evaluate various shielding materials based on effectiveness, weight, and cost.

Main Methods:

• Utilized the MCNP5 Monte Carlo simulation code for dose rate calculations and shielding design.
• Investigated multiple shielding materials including paraffin, borated-paraffin, lead, copper, tungsten, and bismuth.
• Calculated dose rates considering neutrons from Am-Be, gamma rays from Am-241 decay, C-12 de-excitation, and neutron interactions.

Main Results:

• Identified an optimal shielding configuration comprising 10 cm paraffin wax, 2.5 cm lead, and 31.5 cm borated paraffin wax.
• Achieved a reduced effective dose rate meeting the International Commission on Radiological Protection (ICRP) safety requirement of 10 μSv/h.
• The optimized shielding resulted in a compact cubic facility with an overall length of 104.2 cm.

Conclusions:

• The proposed shielding design effectively mitigates neutron and gamma radiation from the Am-Be source.
• The combination of paraffin, lead, and borated paraffin provides a cost-effective and efficient shielding solution.
• The study provides a validated design for safe operation of Am-Be irradiation facilities, ensuring occupational health standards are met.