Measurement of the Cross Section for the ⁷Li(n,n't)⁴He Reaction in the 7- to 9-MeV Energy Range

Cross sections for the ⁷Li(n,n't)⁴He reaction have been measured in the 7- to 9-MeV energy range. The tritium produced in encapsulated lithium metal samples by fast neutron bombardment was extracted and the activity measured using liquid scintillation counting techniques. The neutron fluence was measured with an ion chamber containing a ²³⁸U deposit. This deposit was calibrated by comparing it with standard ²³⁵U deposits. As a result, the error in the (n,n't) cross section is insensitive to the ²³⁸U fission cross-section error but does depend directly on the error in the ²³⁵U fission cross section. The experimental results show that the ⁷Li(n,n't)⁴He cross section is very insensitive to neutron energy in the 7- to 9-MeV range, and the value 372 mb (±3.8%) was obtained for the average cross section in this region.