Research paper An inter-laboratory comparison of cosmogenic 3 He and radiogenic 4 He in the CRONUS-P pyroxene standard P.-H. Blard a, * , G. Balco b , P.G. Burnard a , K.A. Farley c , C.R. Fenton d , R. Friedrich e, f , A.J.T. Jull g , S. Niedermann d , R. Pik a , J.M. Schaefer e, f , E.M. Scott h , D.L. Shuster b, i , F.M. Stuart j , M. Stute e , B. Tibari a , G. Winckler e, f , L. Zimmermann a a CRPG, Universit e de Lorraine, UMR 7358, CNRS, Vandoeuvre-l es-Nancy, France b Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA, USA c Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA d Deutsches GeoForschungsZentrum GFZ, Potsdam, Germany e Lamont-Doherty Earth Observatory, Geochemistry, Palisades, NY, USA f Department of Earth and Environmental Sciences, Columbia University, New York, NY, USA g Department of Geosciences, NSF Arizona AMS Laboratory, Tucson, AZ, USA h School of Mathematics and Statistics, University of Glasgow, Glasgow, Scotland, UK i Department Earth and Planetary Science, University of California, Berkeley, CA, USA j Scottish Universities Environmental Research Centre, Glasgow, UK article info Article history: Received 1 February 2014 Received in revised form 27 August 2014 Accepted 28 August 2014 Available online xxx Keywords: Cosmogenic 3 He Radiogenic 4 He CRONUS-P Standard Calibration abstract This study reports an inter-laboratory comparison of the 3 He and 4 He concentrations measured in the pyroxene material CRONUS-P. This forms part of the CRONUS-Earth and CRONUS-EU programs, which also produced a series of natural reference materials for in situ produced 26 Al, 10 Be, 14 C, 21 Ne and 36 Cl. Six laboratories (GFZ Potsdam, Caltech Pasadena, CRPG Nancy, SUERC Glasgow, BGC Berkeley, Lamont New York) participated in this intercomparison experiment, analyzing between 5 and 22 aliquots each. Intra-laboratory results yield 3 He concentrations that are consistent with the reported analytical un- certainties, which suggests that 3 He is homogeneous within CRONUS-P. The inter-laboratory dataset (66 determinations from the 6 different labs) is characterized by a global weighted mean of (5.02 ± 0.12)  10 9 at g 1 with an overdispersion of 5.6% (2s). 4 He is characterized by a larger variability than 3 He, and by an inter-lab global weighted mean of (3.60 ± 0.18)  10 13 at g 1 (2s) with an over- dispersion of 10.4% (2s). There are, however, some systematic differences between the six laboratories. More precisely, 2 lab- oratories obtained mean 3 He concentrations that are about 6% higher than the clustered other 4 labo- ratories. This systematic bias is larger than the analytical uncertainty and not related to the CRONUS-P material (see Schaefer et al., in this issue). Reasons for these inter-laboratory offsets are difficult to identify but are discussed below. To improve the precision of cosmogenic 3 He dating, we suggest that future studies presenting cosmogenic 3 He results also report the 3 He concentration measured in the CRONUS-P material in the lab(s) used in a given study. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Cosmogenic 3 He is a powerful dating tool that can be used in a large range of geological applications. First, it is the best-suited cosmogenic nuclide for mafic minerals such as olivine or pyrox- ene (e.g. Ackert et al., 2003; Bruno et al., 1997), minerals in which 10 Be cannot be used in a straightforward way (Blard et al., 2008; Ivy-Ochs et al., 1998). Second, it is not affected by radioactive decay, a property that theoretically permits dating very old land- scapes or geological events (e.g. Margerison et al., 2005; Schaefer et al., 1999). Third, 3 He can also be combined with another cosmogenic nuclide in the same sample, such as 36 Cl or 10 Be. Such a multi-isotope study allows determination of complex exposure histories and dating of burial events. Fourth, 3 He is the cosmogenic nuclide having one of the lowest detection limit/production rate ratios (together with 10 Be), which also allows measurement of * Corresponding author. E-mail address: blard@crpg.cnrs-nancy.fr (P.-H. Blard). Contents lists available at ScienceDirect Quaternary Geochronology journal homepage: www.elsevier.com/locate/quageo http://dx.doi.org/10.1016/j.quageo.2014.08.004 1871-1014/© 2014 Elsevier B.V. All rights reserved. Quaternary Geochronology xxx (2014) 1e9 Please cite this article in press as: Blard, P.-H., et al., An inter-laboratory comparison of cosmogenic 3 He and radiogenic 4 He in the CRONUS-P pyroxene standard, Quaternary Geochronology (2014), http://dx.doi.org/10.1016/j.quageo.2014.08.004