Synthetic multi-element standards (SMELS) used for the validation of K0-NAA

As more and more labs dealing with nuclear analytical techniques are working under a quality assurance system, the need for demonstrating the analytical quality of the method becomes increasingly important. For non-standard methods, such as k0-standardisation Neutron Activation Analysis (k0-NAA), this means a full validation report demonstrating amongst others the bias and the reproducibility of the method and a continuous quality control using appropriate control material. In environmental laboratories using chemical techniques for example several multi-element liquid solutions are available for this purpose. For k0-NAA a set of synthetic multi-element standards (SMELS) was made in cooperation with INW, Gent (B) and IRMM, Geel (B). The SMELS material is based on a phenol formaldehyde resin (Bakelite) that was spiked with 33 different elements. Three types of materials were produced: (1) type I: Au, Cl, Cs, Cu, I, La, Mn and V; forming short-lived radionuclides after irradiation; (2) type II : As, Au, Br, Ce, Mo, Pr, Sb, Th, Yb and Zn; forming medium-lived radionuclides ; (3) type III : Au, Co, Cr, Cs, Fe, In, Sb, Sc, Se, Sr, Th, Tm, Yb, Zn and Zr; forming long-lived radionuclides. These elements have cross-sections and resonance energies with Q0-values ranging from very low to very high and thus serve as quality control of the irradiation facility and the calibration of detectors. The homogeneity of the material was demonstrated by IRMM for a minimum sample intake of 50 mg. In the reactor of Rez near Prague it was proven that the Bakelite matrix has an excellent radiation stability and this up to high fluence density of both thermal and fast neutrons (up to 1.1014 n.cm-2.s-1 and 3.1013 n.cm-2s-1 respectively)