Monte Carlo estimate of particle fluxes in thin cylindrical detectors

An algorithm is proposed for greatly accelerating Monte Carlo calculations of the indications of neutron flux detectors whose linear dimensions are much greater than their thickness and width and whose volume is extremely small. Detectors of this form are often used for performing measurements inside a core. Activation detectors can also be of this type. In contrast to existing methods for estimating flux at a point, the proposed algorithms do not require explicit calculation of the conditional probability density for scattering as a function of energy and direction. Only the azimuthal symmetry of scattering and the anisotropy of fission neutrons are used. A method is proposed for implementing the algorithm that does not require any changes in the physical module of the Monte Carlo program. The question of the variance of the estimates is discussed and a method that guarantees a finite variance is proposed.