A practical method for measuring the boron equivalent of graphite impurity

A question of graphite purity testing is discussed in the context of the Nuclear Non Proliferation Treaty. A practical method for measuring the boron equivalent of graphite impurity via comparing the thermal neutron absorption in standard and test graphite samples is described. An experimental assembly comprising 252Cf neutron source is presented. With the use of 300-cm3 ground graphite sample, the value of boron equivalent can be determined to the precision of 0.74 ppm. MCNP simulations showed that the uncertainty of BE determination could be reduced significantly if a larger sample was used.