Estimation of (41)Ar production in 0.1-1.1.0-GeV proton accelerator vaults using FLUKA Monte Carlo code

Area of Science:

• Nuclear Physics
• Accelerator Science
• Radiation Protection

Background:

• Accelerator operations produce radioactive isotopes like Argon-41 (41Ar).
• Current empirical formulas for 41Ar estimation often rely on thermal neutron activation.
• These formulas may not fully account for the neutron energy spectrum in accelerator vaults.

Purpose of the Study:

• To estimate 41Ar concentration in accelerator vaults using FLUKA Monte Carlo simulations.
• To compare simulation results with existing empirical methods.
• To identify the contribution of different neutron energies to 41Ar production.

Main Methods:

• FLUKA Monte Carlo simulations were employed.
• Simulations modeled proton beams (0.1-1.0 GeV) incident on copper and lead targets.
• Neutron fluence and 41Ar production within vaults of various sizes were analyzed.

Main Results:

• FLUKA simulations and analytical techniques yielded similar thermal neutron fluence.
• The empirical formula significantly under-predicted 41Ar concentration.
• Thermal neutrons accounted for ~41% of 41Ar production, while epithermal neutrons (0.025-1 eV) contributed 56%.

Conclusions:

• Empirical formulas based solely on thermal neutrons are insufficient for accurate 41Ar estimation.
• A modified factor is recommended for empirical expressions to better estimate 41Ar activity.
• Understanding neutron energy contributions is crucial for radiation safety in accelerator facilities.