Evaluation of a 4$pi$ neutron counter for the nondestructive analysis of uranium-234 in uranium hexafluoride

A neutron counter has been evaluated for the nondestructive analysis of $sup 234$U in uranium hexafluoride. The instrument was designed by Los Alamos Scientific Laboratory for the Nuclear Safeguards Program. The method assumes that the only source of neutrons is from $sup 19$F($alpha$, n)$sup 22$Na reaction from $sup 238$U, $sup 235$U, and $sup 234$U, the yield from $sup 234$U being the most abundant. This evaluation shows that the mean of the difference between the 4 $pi$ neutron counting method and mass spectrometry is 0.0002 wt percent uranium- 234 +- 0.00015 at the 95 percent confidence level. However, the presence of $sup 232$U produces significant errors in the system. If the neutron technique is to be used for samples containing $sup 232$U in equilibrium with its daughters, the 2.61-MeV gamma peak of $sup 208$Tl must be measured and used to correct for the $sup 232$U. It has been postulated that the neutron counter might also be used to relate the $sup 234$U content of a sample to the $sup 235$U, thus estimating the $sup 235$U concentration. This evaluation notes, however, that in a variety of uranium feeds and enriched product, the $sup 234$U/$sup 235$U ratio varies too widely to enable a valid $sup 235$U determination