Absolute Fission Rate Measurements with Solid-State Track Recorders

The method of fission track counting has been placed on a precise absolute basis. Sources of systematic error have been investigated and eliminated or reduced so that precise fission rate measurements can be conducted. Solid State Track Recorders (SSTR) of pre-etched mica and polycarbonate resin (Makrofol) have been used. Experimental results depend critically on the quality of the fission sources employed. Consequently, different methods of fission source preparation have been examined. The efficiency and sensitivity of this method have been determined for both mica and Makrofol. An irradiation assembly providing uniform neutron flux exposures is used for relative measurements. Absolute calibrations have been carried out with ²⁴⁴Cm spontaneous fission sources. A limiting accuracy of close to 1% for absolute uranium fission rate measurements has been achieved.