Electron accelerator-driven photoneutron source for clinical environments.

摘要

There are several potential uses for a high-flux thermal neutron source in both industrial and clinical applications. The viable commercial implementation of these applications requires a low cost, high-flux thermal neutron generator suitable for installation in industrial and clinical environments. This dissertation describes the MCNP modeling results of a high-flux thermal neutron source driven with an electron accelerator. An electron linac, fitted with a standard x-ray converter, can produce high neutron yields in materials with low photonuclear threshold energies, such as D and 9Be.; Calculations were performed using the Monte Carlo for N-Particle (MCNP) transport code. Modeling results indicate that a 10 MeV, 10 kW electron linac can produce on the order of 1012 n/s in a heavy water photoneutron target.{09}A 40 cm radius, 60 cm long cylindrical heavy water photoneutron target has a photoneutron production rate equal to 5.7 × 1012 n/s. The thermal neutron flux in an unreflected, 40 cm radius, 60 cm long heavy water target is calculated to be 9.81 × 109 n/cm 2/s. The sensitivity of these answers to heavy water purity was investigated, specifically, the dilution of heavy water with light water. It was shown that the peak thermal neutron flux in an unreflected target was not adversely effected by dilution up to a light water weight fraction of 25%.; The final design consists of a 40 cm radius, 60 cm long cylindrical photonuclear target reflected on all sides with 20 cm of polyethylene. The polyethylene reflector increases the maximum thermal neutron flux by 66%, to 1.40 × 1010 n/cm2/s using a 10 MeV, 1 mA (10 kW) electron linac. At this flux level the device is capable of producing 831 μCi/mg of 165Dy from natural dysprosium. The device is capable of producing 160 μCi/mg of 198Au at this flux.; The neutron shielding required for the device consists of 5 cm of 5% borated polyethylene (BPE) on the front of the device, 4.25 cm of BPE on the side, and 8.5 cm of BPE on the back of the device.{09}The photon shielding requires an additional 46 cm (1.5 ft) of lead on the front and back, and 40 cm of lead on the side of the device. This amount of shielding will reduce the dose equivalent rate at 30 cm from photons and neutron combined to less than 10 mrem per week with a ¼ occupancy factor.