A novel route to produce a homogeneous certified reference material for k 0 -neutron activation analysis: Application to the certification of gold mass fraction in an Al–0.1% Au alloy T. Bacquart a, ⁎, J.H. Li b , S. Ribeiro Guevara c , M.A. Arribére c , T. Gerganova a , M. Sterckx d , P. Schumacher b , T.P.J. Linsinger a a European Commission—Joint Research Centre—Institute for Reference Materials and Measurements, Retieseweg 111, 2440 Geel, Belgium b Institute of Casting Research, University of Leoben, Franz-Josef Str. 18, A8700 Leoben, Austria c Laboratorio de Análisis por Activación Neutrónica, Centro Atómico Bariloche, CNEA, Av. Bustillo km 9.5, 8400 Bariloche, Argentina d UMICORE Analytical Competence Center, Watertorenstraat 33, Olen, Belgium abstract article info Article history: Received 22 July 2015 Accepted 12 August 2015 Available online 20 August 2015 Keywords: k 0 -neutron activation analysis CRM production ERM-EB530 Microhomogeneity Al–0.1%Au Inter-comparison Reliable certified reference materials (CRM) are required for neutron dosimetry in k 0 -neutron activation analysis (k 0 -NAA). In the past, levitation melting was employed to produce highly homogeneous alloys used in the pro- duction of CRMs. This publication describes a novel and more efficient way of processing such alloys using the example of an Al–Au alloy, the evaluation of the efficacy with respect to achieving homogeneity and avoiding micro- and macrosegregation and the final certification of the Au mass fraction. First, Al–5% Au alloy was melted by arc melting and then diluted into Al–0.1% Au with high purity Al in a resistance furnace under the protection of high purity argon gas. The as-casted Al–0.1% Au was then heat-treated at about 635 °C for 48 h. No significant macrosegregation and no intermetallic phase (AuAl 2 ) were observed in the heat-treated alloy. Using this ap- proach, a new CRM for gold mass fraction in Al–0.1% Au was produced in the form of wires and foils (ERM- EB530A, B and C). The relative uncertainty from gold inhomogeneity in the material was assessed using a randomised block design and inductively coupled plasma optical emission spectrometry (ICP-OES) and was found to be 0.3%. The characterisation of the gold mass fraction was performed by an interlaboratory comparison of expert laboratories. Sixteen laboratories participated using instrumental neutron activation analysis ( 197 Au(n,γ) 198 Au), fire assay and ICP-OES. Alternative INAA reactions ( 197 Au(n,2n) 196 Au) and calibration strate- gies were tested but not retained for the characterisation study as they did not meet the strict performance criteria set for the study. After evaluation of homogeneity and characterisation, the Au mass fraction in ERM- EB530A, B and C was certified to be 1005 ± 7 mg/kg (k = 2), which is a lower uncertainty than for previous sim- ilar materials. This demonstrates the suitability of the new production route, which should also be applicable to other binary alloys required for neutron dosimetry. © 2015 Elsevier B.V. All rights reserved. 1. Introduction For the past 50 years, certification of reference materials (RM) for neutron dosimetry has been carried out at the JRC—Institute for Refer- ence Materials and Measurements (IRMM), the former Central Bureau of Nuclear Measurements (CBNM) [1], in support of the nuclear physics community. Neutron dosimetry requires reference materials that are very homogeneous at the microscale level (samples size b 1 mg) [2] and have reliable certified values and low uncertainties of the certified properties (expanded uncertainty b 1%). The major problem for the production of a RM alloy is the potential metallurgical segregation within individual grains (i.e. microsegregation) or along the material (i.e. macrosegregation). Segregations can be caused by a number of complex processes which are influenced by the diffusion rate, cooling rate and homogeneity of the melt [3]. As conventional melt- ing and casting techniques were not considered as being able to completely avoid these influences, levitation melting was frequently used to produce the alloy for neutron dosimetry CRMs in the past [2,4]. The advantage of levitation melting is the high degree of homogeneity through electromagnetic stirring and rapid solidification [4]. Numerous CRMs were successfully prepared for neutron dosimetry following this route such as an Al–0.1% Au alloy (IRMM-530R and IRMM-530) [5], Al–0.1% Co (IRMM-527) or Al–1.0% Co (IRMM-528) [4]. However, the dis- advantage of levitation melting for CRM production is the small size of the production batch. Each production batch is limited to about 20 g, which requires combination of many batches to produce sufficient material for one CRM. Slight variations between batches may lead to additional Microchemical Journal 124 (2016) 159–166 ⁎ Corresponding author. Tel.: +44 7754 179539. http://dx.doi.org/10.1016/j.microc.2015.08.005 0026-265X/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Microchemical Journal journal homepage: www.elsevier.com/locate/microc