Tritium production in He-3 gas cells immersed in the Tokamak Fusion Test Reactor neutron field

Tritium generated in an external cell by the reaction He-3(n, p) T can be u sed as a gauge of long-term fusion neutron production, because of the 12-ye ar half-life of T and the relative ease of measuring the T content either b y sampling or from the saturation current of the cell when operated as an i onization chamber. Two high-pressure He-3 gas cells enclosed in polyethylen e neutron moderators were exposed to Tokamak Fusion Test Reactor (TFTR) neu trons during high-power D-T operation. The tritium produced in the cells wa s assayed by the Princeton Differential Atmospheric Tritium Sampler. The me asured tritium generated per 10(19) fusion neutrons was 510 pCi/cc at 2.3 m from the TFTR vessel and 1.3 m below the midplane, and 2020 pCi/cc at 1.0 m from the TFTR vessel in the midplane. Combining these results with previo us measurements at a third location, we found 0.11 to 0.23 triton produced per neutron incident on the projected cell cross section, with an asymptoti c local tritium breeding ratio of 0.32. (C) 1999 American Institute of Phys ics. [S0034-6748(99)68101-1].