Clinical 6 MV X-Ray facility photo-neutron/fission interrogations with TMFD sensors

Detection of several targets (U, Be, D2O) of interest to national security has been achieved at Purdue University’s 6 MV X-ray clinical linear accelerator (CLINAC), from photoneutron/fission induced neutron signatures using a Centrifugally Tensioned Metastable Fluid Detector (CTMFD). Traditional neutron detection schemes were saturated and ineffective under the intense (to ∼104 R/h) photon environment; however, the CTMFD sensor technology was capable of measuring the relatively low (∼1012x lower intensity) neutron field produced from 6 MeV-end point X-ray beam interactions with the CLINAC components and surroundings. This is in stark contrast to published results based on the conventional belief that the neutron dose component in 6 MV CLINAC facilities is immeasurable over the background photon background dose. Photoneutron and photofission neutron production rates were detected and analyzed at various standoffs from the isocenter, with and without special nuclear material (SNM) related targets ranging in mass from 5 g of Be, to ∼0.6 kg of UO2. It was confirmed that 6 MV X-ray photons do result in measurable neutron dose above normal cosmic background. Additionally, in threshold mode, the CTMFD operating under a tensioned metastable pressure of -5 bar, enabled conclusive rejection of background photoneutrons, while enabling the rapid detection of: Be, D2O, C and U targets within seconds to minutes while operating in and around 104 R/h photon fields.