H-2 Production In The B-10(N,Alpha)Li-7 Reaction In Water

We demonstrate a method for measuring the H-2 produced in water from the B-10(n,alpha)Li-7 fission reaction. Low energy neutrons from the NIST Center for Neutron Research interact with borate-containing water in a temperature-controlled high pressure cell made from titanium. After exposure for one to several hours, the water is extracted and sparged with argon. H-2 entrained in the sparging gas is sampled with a small mass spectrometer. To determine the neutron exposure, a small amount of sodium is included in the borate solution. The water is collected and Na-24 activation is measured in a counting apparatus on the following day. The G-value for H-2 at room temperature is found to be (1.18 +/- 0.10) molecules H-2/100eV, in good agreement with previous estimates and recent modeling calculations.