H2 generation by the 10B(n,& alpha;)7Li reaction in high temperature water

H2 produced in water from the 10B(n,& alpha;)7Li fission reaction has been measured up to 300 degrees C. Thermal energy neutrons from the Rhode Island Nuclear Science Center's 2 MW reactor interact with boric acid-containing water in temperature-controlled high-pressure cells made from tubing of either titanium or zirconium alloy. After exposure for a minimum of 1 h, the solution sample is extracted and sparged with argon. The H2 entrained by the sparging gas is sampled with a small mass spectrometer. A small amount of sodium is included in the boric acid solution so that after sparging, samples can be collected for 24Na activation measurements in a gamma spectrometer to determine the neutron exposure and thus the total energy deposited in solution. The G-value (& mu;mol/ J) for H2 production is obtained for water at a pressure of 25 MPa, over a temperature range from 20 degrees C to 300 degrees C. The weak temperature dependence of this yield between 150 degrees C and 200 degrees C demonstrates that the bimolecular reaction of pairs of e-aq is a very minor source of H2 in high LET tracks.