Hotelling's Test Applied to Measured Isotopic Compositions of Plutonium

Non-destructive gamma spectrometric measurements of the isotopic composition of plutonium with high resolution detectors are routinely carried out in the framework of nuclear safeguards inspections. Spectra de-convolution is then performed by means of special codes, such as MGA, which deliver as result a vector of five isotopic abundances of 238Pu, 239Pu, 240Pu, 241Pu and 241Am with associated uncertainties. Up to now, the decision upon agreement or disagreement between measured and declared values is based mainly on one isotope, actually 240Pu. In the present work, a multivariate test, actually Hotelling’s T2 test, involving the comparison of the whole vector of experimental values with the vector of the declared values is studied. This is done on the experimental basis of 125 series of 250 gamma spectrometric measurements which were made with 15 detectors using Cd or Fe as filters, on a variety of Pu samples ranging from weapons material to reactor Pu. It was found that the measured isotopic abundances obey a non-central T2 distribution. This non-centrality is strongly reduced if the MGA value of the gamma branching ratio of 241Pu is slightly reduced. It was observed that the average T2 of a series is correlated with the MGA fit quality parameter NQFit of the spectra and that the upper limit T2 99% of the distribution depends on the Pu isotopic composition.

BERNDT R.;  MORTREAU Patricia; 

2023-01-10

ELSEVIER SCIENCE BV

JRC129670

0168-9002 (online),   

https://www.sciencedirect.com/science/article/pii/S0168900222010798?via%3Dihub,    https://publications.jrc.ec.europa.eu/repository/handle/JRC129670,   

10.1016/j.nima.2022.167787 (online),