Studying the structure of liquid and solid 3He by passing neutrons through a layer of matter is difficult due to the large cross section of the exothermic reaction 3He(n,p)3H, which for neutrons with an energy of 300 K is equal to 5400 bn. Determine the neutron energy with which you can study 1 mm thick layers of 3He so that at least 10% of the incident neutron flux passes through them. The concentration of 3He nuclei is n = 1022 cm-3. The cross section of this reaction for neutrons with energies up to 1 MeV is non-resonant

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