Relative efficiency calibration for determining isotopic composition and age of HEU items by passive non-destructive gamma spectrometry.

ABSTRACT

The observation of the 239 keV gamma line from 232U decay in high-enriched uranium (HEU) samples prompted us to utilize 232U (with main gamma energies of its daughters at 239, 583, 763, and 860 keV) as a mediator isotope for performing relative (intrinsic) efficiency calibration among 232U, 234U, 235U, 238U, and 214Bi isotopes. By this way, the isotopic composition and age of HEU samples can be derived from activity ratios constituted between pairs of these isotopes on the basis of a common relative efficiency calibration curve. The method proved to be a useful tool for γ-spectrometric characterization of HEU items, especially of weapon grade, shielded uranium material.