Neutron-gamma dosimetry for BNCT using field oxide transistors with gadolinium oxide as neutron converter layer.

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.

A Gadolinium Metal-Organic Framework Film as a Converter Layer for Neutron Detection.

Metal-organic frameworks (MOFs) are known for their versatility in terms of their crystalline structure, porosity, resistance to temperature, radiation damage, and luminescence among others. Gadolinium (Gd) is one of the elements with the highest reported cross-section for low energy neutron capture, producing internal conversion electrons and γ rays as a result of the neutron absorption. The development of Gd-BTC films (BTC=1,3,5-benzenetricarboxylate) is shown that were deposited on Si and Al substrates by airbrushing, and characterized by profilometry, Raman, EDX and X-ray diffraction. Radiation damage, thermal decomposition and neutron absorption of these films were studied as well. Gd-BTC films were attached to CMOS devices (Complementary Metal-Oxide-Semiconductor), which are sensible to the internal conversion electrons, in order to build a neutron detector. The devices Gd-BTC/CMOS could selectively detect neutrons in the presence of γ rays with a thermal neutron detection efficiency of 3.3±0.1 %, a signal to noise ratio of 6 : 1, and were suitable to obtain images.