Study of the radiation environment during 1H irradiation of metallic natMo target: The accelerator pathway for 99mTc production

Abstract

Objective

Growing requirement of ⁹⁹Mo for cancer diagnosis need urgent alternative from the conventional enriched ²³⁵U based reactor technology considering its proliferation potential, prolonged operations for decades needing refurbishment and major upgrades and elaborate distribution network for catering the worldwide requirements. Previously, the reactor shutdown at NRU in 2009 and distribution disruption in 2020 due to COVID-19 has showed the need of a localized ⁹⁹Mo production setup. The proton accelerator pathway can be an efficient solution for a compact and low cost ⁹⁹Mo production facility. However, studies regarding the radiation protection and decommission plan need to be explored beforehand.

Methods

Present work focuses on the quantification of secondary radiations (neutron and photon) emitted during proton bombardment on natural Mo target during ⁹⁹Mo and/or ⁹⁹Tc production. Experiments were performed at BARC-TIFR Pelletron Facility, India with proton bombardment on thick Mo targets with incident energies between 8 and 22 MeV followed by measurement of secondary emission spectra and the ambient dose equivalents.

Results

The measured emission neutron ambient dose equivalents are found to dominate over photons and the neutron peak energy remains almost invariant in the entire incident proton energy range. However, the neutron fluence enhances significantly with an enhancement factor of 60 as the proton energy increases from 8 to 22 MeV. The photon ambient dose equivalent rates were found to increase by more than 30 times with increasing proton energies.

Conclusion

The results clearly indicate that during design of a compact accelerator-based facility for ⁹⁹Mo production need careful consideration regarding secondary radiations.