A method for determining fast neutron energies in a large sample

The energy of 14 MeV monoenergetic neutron generated by the T(d,n)4He reaction as a function of the d beam emergent angle, En(θ), is considered. Based on the geometric size of the experimental sample and the position of the sample relative to the T–Ti target, a theoretical formula for calculating the mean neutron energy irradiating a large sample is obtained. This formula is related to the distance L between the sample and the T–Ti target, to the emergent angle β and the radius of the sample R. Using the Zr/Nb method, a fitting formula for the mean neutron energy is derived based on the evaluated values of the 90Zr(n,2n)89m+gZr and 93Nb(n,2n)92mNb reaction cross-sections. Combining this formula with the measured σ(Zr)/σ(Nb) ratio, the mean neutron energy irradiating a large sample was obtained. The theoretical calculations and the experimental measurements show that our formula can be used to determine the mean neutron energy irradiating on a large sample.

► The method is proposed to determine the mean neutron energy irradiating on the large sample.
► The theoretical formula for the calculation of the mean neutron energy is obtained.
► A fitting formula for the mean neutron energy is derived.
► The results of theoretical calculation compared with the fitting results.