Determination of gold in Romanian auriferous alluvial sands and rocks by 14 MeV neutron activation analysis Roxana Lupu a,b , Alexandrina Nat b,c , Antoaneta Ene c, * a Chemistry–Physics Section, Faculty of Chemistry, Babes-Bolyai University of Cluj-Napoca, Romania b Activation Laboratory, Nuclear Unit, ISPAT-SIDEX Iron and Steel Works, Galatzy, Romania c Department of Physics, Faculty of Sciences, Dunarea de Jos University of Galatzy, Domneasca 111, 800201 Galatzy, Romania Received 20 May 2003; received in revised form 16 September 2003 Abstract In this work a complex study of the nuclear and spectral interferences which appear in gold determination by 14 MeV neutron activation analysis of Romanian auriferous alluvial sands and rocks has been accomplished. The contributionofthenuclearinterferingelements–HgandPt–totheconcentrationofgoldinthesamplesisminimumin the case of the nuclear reactions 197 Au(n, 2n) 196 Au, 197 Au (n,2n) 196m Au and 197 Au(n, n 0 ) 197m Au. As regards the spectral interferences, these are minimum in the case of using the reactions 197 Au(n, n 0 ) 197m Au and 197 Au (n, 2n) 196 Au and are due to Rb, Ti and V for the short irradiation and to Se for the long irradiation. We propose two methods of gold determinationinauriferousalluvialsandsandrocksintherange20–2500ppm–theminimumvalueof20ppmbeingat the level of an economic extraction – in the optima conditions established by us so that the systematic errors of analysis due to the gold accompanying elements should be considerably diminished: a method using short irradiation (25 s) and NaI(Tl) spectrometry for the measuring of the induced gamma radioactivity in the samples and a method using long irradiation (3000 s) and Ge(Li) spectrometry. The data presented in this paper can be adapted by other analysts to the rapid determination of gold in a variety of alluvial sands and rocks. Ó 2003 Elsevier B.V. All rights reserved. PACS: 82.80.J Keywords: Gold determination; Analysis of auriferous alluvial sands and rocks; Neutron activation analysis; 14 MeV neutrons; Interference effects 1. Introduction Many world laboratories have developed ana- lytical methods of determining the chemical and isotopic composition of rocks, minerals, ores and other natural materials. They include classical chemical techniques and atomic or nuclear spec- trometric techniques such as atomic absorbtion spectroscopy (AAS) and emission spectroscopy (ES), inductively coupled plasma mass spectro- metry (ICP-MS), accelerator mass spectrometry (AMS), X-ray fluorescence (XRF), particle- induced X-ray emission (PIXE), neutron activa- tion analysis (NAA) using thermal and 14 MeV * Corresponding author. Tel.: +40-236-414-871; fax: +40- 236-460-135. E-mail address: aene@ugal.ro (A. Ene). 0168-583X/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2003.09.031 Nuclear Instruments and Methods in Physics Research B 217 (2004) 123–135 www.elsevier.com/locate/nimb