Long-term performances of the 95ZR/95Nb chronometer for nuclear events dating

• An air filter spiked with fission products was analyzed by gamma-ray spectrometry.
• T0 of the fictitious nuclear explosion was determined using 95Zr/95Nb chronometer.
• Very accurate dating can be obtained even after several months of decay.
• To avoid GUM limitations, uncertainties were assessed using Monte Carlo simulation.
• Practical limitations of this chronometer in actual situations are investigated.

The present work reports on a long-term analysis of the performances of the 95Zr/95Nb chronometer for dating a nuclear event. Taking benefit of a recent Profiency Test Exercise, a sample containing a standardized mixture of fission products has been measured repeatedly with a low background HPGe spectrometer during a period extending up to one year with the aim of assessing the accuracy of the various zero-time determinations. Evaluation of the uncertainties associated to these evaluations was performed using a Monte Carlo approach. Input parameters sensitivity has been investigated, especially the influence of the 95mNb decay branch. The 95Zr/95Nb chronometer was found to be accurate for zero-time determination within one day and one week for a decay of 3 months and 10 months respectively. Sub-day uncertainties are achievable for a two months old sample whereas sub-week uncertainties are reached after a decay of six months. Limitations of the technique for dating a real event are investigated.