New method for measuring the time integral of neutron flux in a reactor

摘要

A new method for measuring the time integral of thermal neutron flux of a nuclear reactor is proposed. This method utilizes two consecutive (n,γ) reactions on the58Ni isotope of a natural nickel sample placed near the core of a reactor,58Ni(n,γ)→59Ni(n,γ)→60Ni(n,γ). Natural nickel contains 68%58Ni producing an intense 8.999 MeVγ-line leading to the59Ni ground state via the58Ni(n,γ) reaction. The59Ni isotope produced in this manner undergoes another (n,γ) reaction, emitting aγ-line at 11.388 MeV leading to the60Ni ground state. By measuring the intensity ratio of the twoγ-lines at 8.999 and 11.388 MeV using a HPGe detector, it is possible to deduce the integral over time of the neutron flux necessary for producing the59Ni isotope. Good accuracy can be obtained with this method due to the low gamma background at such high energies.