Fluid inclusion depth and thickness estimates using a Na nuclear reaction resonance and Si elastic scattering B. M enez a, * , P. Philippot a , M. Bonnin-Mosbah b , F. Gibert c a CNRS-ESA 7058, Laboratoire de P etrologie, T26-0 E3, case 110, 4 place Jussieu, Universit e Paris 7, 75252 Paris Cedex 05, France b Laboratoire Pierre S ue, CEA-CNRS, CE Saclay, 91191 Gif Sur Yvette Cedex, France c CNRS-URA 10, Universit e de Clermont Ferrand, 63038 Clermont Ferrand, France Abstract An important aspect of quantitative ¯uid inclusion analysis using X-ray emission techniques concerns a knowledge of ¯uid inclusion depth and geometry to establish reliable absorption correction procedures. The aim of this study is to assess the potential performance of the nuclear reaction 23 Na(p, p 0 c) 23 Na in estimating inclusion depth. Na was chosen because of its common occurrence in natural ¯uids. The nuclear reaction displays a characteristic, low energy resonance peak at 1.283 MeV in its cross-section which, together with recognition that the energy of the incident particles tra- versing matter decreases predictably with depth, allow estimation of the thickness of quartz traversed by the beam and hence the inclusion depth. Results of the calculation shows accuracy on estimated ¯uid inclusion depths commonly better than 0.5 lm. In addition, following the same experimental protocol as de®ned for Na, we show how the use of the elastic scattering reaction 28 Si(p, p) 28 Si can provide information on the ¯uid inclusion thickness. Ó 1999 Elsevier Science B.V. All rights reserved. PACS: 91.65.Vj; 24.30.Gd; 25.40.Cm; 25.40.Ep Keywords: Fluid inclusion; Nuclear reaction analysis; Elastic scattering 1. Introduction Fluid inclusions are tracers of ¯uid circulation in crustal rocks, and a knowledge of the compo- sition of trapped ¯uids is necessary for recon- structing paleo-hydrothermal processes. Most natural minerals, however, contain several gener- ations of ¯uid inclusions of dierent compositions, each of which is associated with a distinct hydro- thermal event. As a consequence, quantitative analysis of single ¯uid inclusions is required to extract information relevant to the evolution of hydrothermal systems. The Proton Induced X-ray Emission (PIXE) and Synchrotron X-Ray Fluorescence (SXRF) techniques have proved to be well-adapted for trace element analysis of individual ¯uid inclusions [1±8]. However, the computational procedures used for estimating elemental concentrations re- quire corrections for X-ray absorption by the Nuclear Instruments and Methods in Physics Research B 158 (1999) 533±537 www.elsevier.nl/locate/nimb * Corresponding author. Fax: +33-1-44-27-39-11; e-mail: menez@ccr.jussieu.fr 0168-583X/99/$ - see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 3 5 0 - X