Evaluation of Neutron Spectra in the Linear Accelerator Facility of the Philippine General Hospital using an Indium-Based Multishell Neutron Spectrometer (In-MuNS)

Abstract

The neutron energy spectra of the 10 megavolt linear accelerator at the Philippine General Hospital (PGH) were evaluated using an Indium-based Multi-shell Neutron Spectrometer (In-MuNS). Measurements were conducted by employing an indium foil central detector within several high-density polyethylene spherical shells irradiated under fixed conditions. Indium activation foils utilize the neutron detection reaction ¹¹⁵In(n,γ) ^116mIn, emitting ^116mIn gamma rays which were counted using a NaI(Tl) scintillation detector. Gamma spectrometry was then conducted to calculate the induced saturation activities. The Frascati Unfolding Interactive Tool (FRUIT) code, along with pre-validated In-MuNS response functions, were utilized to derive the neutron spectrum and ambient equivalent dose. The unfolding process revealed a total neutron fluence of 1.09×10⁵ cm⁻² Gy⁻¹ at the isocenter, and 4.29×10⁴ cm⁻² Gy⁻¹ at 70 cm away from the isocenter. The calculated ambient dose equivalent in air, H^∗ (10), at the two locations are 17.75 µSv/Gy and 5.60 µSv/Gy. The results can support local medical physicists in radiation protection against neutron contamination in LINAC facilities.