Large Sample Neutron Activation Analysis: correction for neutron and gamma attenuation

Most analytical techniques do not comply with the need for direct trace element analysis of samples exceeding the order of grams. Instead, sub-sampling methods are used to obtain representative sampling of the initial material. The possibilities arising from directly analyzing voluminous samples have been discussed [4]. Instrumental Neutron Activation Analysis (INAA) is a powerful technique, which can fulfil this need in a non-destructive way. For the quantitative analysis of large samples three parameters must be taken into consideration: neutron self-shielding during neutron irradiation, gamma ray attenuation within the sample during counting, and detector efficiency over the volume source. At the GRR-1 research reactor, a LSNAA facility is under development for non-destructive determination of the elemental composition of large volume samples (i.e. volume up to ~5 liters). In the present work, the design of the facility is presented, as well as methods to correct the data for neutron and gamma ray self-shielding effects. The derivation of correction algorithms was based on modelling in detail, both the irradiation and counting facility using the Monte Carlo neutron photon transport code MCNP-4C [5]. Both the code and the cross-section data package were obtained from NEA Data Bank (France). The results of the computations were validated against experimental measurements. Large Sample Neutron Activation Analysis: correction for neutron and gamma attenuation Faidra Tzika, Ion E. Stamatelatos, John Kalef-Ezra, Peter Bode