Cross calibration of neutron detectors for deuterium-tritium operation in TFTR

During the initial deuterium-tritium experiments on TFTR, neutron emission was measured with ²³⁵U and ²³⁸U fission chambers, silicon surface barrier diodes, spatially collimated ⁴He proportional counters and ZnS scintillators, and a variety of elemental activation foils. The activation foils, ⁴He counters, and silicon diodes can discriminate between 14 and 2.5 MeV neutrons. The other detectors respond to both DD and DT neutrons but are more sensitive to the latter. The proportional counters, scintillators, and some of the fission chambers were calibrated absolutely, using a 14 MeV neutron generator positioned at numerous locations inside the TFTR vacuum vessel. Although the directly calibrated systems were saturated during the highest-power deuterium-tritium operation, they allowed cross calibration of less sensitive fission chambers and silicon diodes. The estimated absolute accuracy of the uncertainty-weighted mean of these cross calibrations, combined with an independent calibration derived from activation foil determinations of total neutron yield, is ±7%.