EU Science Hub

Improved chronometry for monitoring of nuclear explosions

Jul 28 2014

The JRC perfected a method to use the decay of two fission products - 95Zr and 95Nb - as a chronometer for a nuclear event.

This chronometer is an important tool for organisations monitoring compliance with the Comprehensive Test Ban Treaty (CTBT), which is a multilateral agreement among states - adopted by the United Nations General Assembly 1996 - to ban nuclear explosions in all environments.

After a nuclear explosion, fission products may attach to aerosols and be collected on air filters in remote monitoring stations. The detection of gamma-rays from 95Zr and 95Nb not only indicates that a nuclear event took place, it also contains information about when it took place. Up to now, approximate decay formulas were used to calculate the time of an explosion from the relative gamma emission rates of both nuclides, due to the complexity of the decay scheme. Also the uncertainty evaluations were deemed too difficult for analytical calculations and one had to resort to computer simulations.

JRC-Institute for Reference Materials and Measurements (IRMM) has a long-standing experience in radionuclide metrology by which it supports nuclear-based science in line with EU policy. A JRC-IRMM scientist succeeded at deriving an exact mathematical solution for the 95Zr-95Nb chronometer as well as analytical equations for making a complete uncertainty analysis. The validity of the equations was tested in collaboration with the National Physical Laboratory in the UK, demonstrating that the age of a test sample could be calculated back accurately even after one year.


Read more: S. Pomm√© and S.M. Collins, Unbiased equations for 95Zr–95Nb chronometry, Appl. Radiat. Isot. (2014) 90:234-240, doi:10.1016/j.apradiso.2014.04.010