Beam calculation method for a neutron camera

Neutron radiography is an important utilization of research reactors. Therefore, a method that can predict the neutron imaging flux of a neutron camera is a valuable tool. Monte Carlo codes are effective at computing the flux at the core vicinity, but when the domain contains the whole neutron beam channels, simulations are limited since only a fraction of the simulated neutrons arrive at the imaging plane, and thus the statistical error is large. We report the development of an analytic method based on transport theory which, given Monte Carlo calculations of the flux at the reactor core and its vicinity, predicts the flux at the imaging plane. We locate the origins of the ballistic neutron beam, and tally the flux at these sites. This method was validated by comparison with MCNP calculations and with past measurements in the Israeli research reactor 1 (IRR1). As a result, we show that this method may help optimize the IRR1 core for radiography increasing efficiency by 50%. This method is also relevant to different neutron beam sources and applications, such as accelerators and diffractometers.