Zeta: The Ultimate Solution to Fission-Track Analysis Calibration or Just an Interim Measure?

Abstract

Because of the lack of unique system calibration coupled with a low threshold for track annealing, the fission-track (FT) method was perceived in the 1970s as an inadequate and imprecise dating method. System calibration had a multiplicity of λ_f ²³⁸U spontaneous fission-decay constant values and neutron dosimetry schemes with little inter-laboratory standardisation. Differences in methodology also introduced subtle variations into calibrations which often went unrecognised. Resurrection of a comparative calibration approach whereby the multiple dating of carefully selected age standards derived a calibration factor zeta, seemingly circumvented previous problems. Following consensus agreement at the 1988 Besançon FT Workshop, zeta has been adopted by a majority of FT workers and remains the common calibration approach in most published and commercial applications. With advances in neutron fluence dosimetry and evidence of precise experiments to determine λ_f, the case is advanced that zeta should be re-examined and those factors capable of quantification be separated from less readily determinable procedural factors. The danger of such attempts at scientific advance being perceived as a break-up of the calibration consensus is highlighted. Argument is made that applications of the FT method should continue to use existing calibration schemes, with strategies aimed at resolving zeta into its component parts run as parallel projects with no crossover. If and when significant advance in calibration is achieved, the case should be presented to the FT community for a systematic revision following the model of the 1988 Besançon agreement.