Neutron‐Gamma Dosimetry for BNCT using Field Oxide Transistors with Gadolinium Oxide as Neutron Converter Layer

Abstract

Purpose: A new type of electronic dosimeter is presented, capable of discerning between the doses of gamma photons and neutrons in a mixed beam as found in boron neutron capture therapy (BNCT). We introduce a real-time dosimeter based on a thick gate field oxide field effect transistor (FOXFET) covered with a neutron converter layer containing gadolinium. Methods: To sensitize the FOXFET dosimeter to neutron fluxes, a converter layer containing gadolinium oxide particles embedded in photoresines was deposited over the sensor surface. Mixed neutron-gamma field configurations with different neutron energy spectra were used to assess the FOXFET response, considering different thicknesses of the neutron converter layer. Results: The total gamma sensitivity of the devices resulted to be 43 mV/Gy. The responses of sensors with different converter layer thicknesses irradiated with different neutron spectra are simulated using GEANT4 code. The response to photons is not significantly modified with thin conversion layers when used in water medium. Conclusions: A real-time dosimeter comprising a pair of FOXFET sensors—only one of them with a gadolinium neutron converter layer—allows the simultaneous measurement of gamma dose and neutron flux during BNCT irradiations.