Radiation Measurements 39 (2005) 665 – 668 www.elsevier.com/locate/radmeas U and Th thin film neutron dosimetry for fission-track dating: application to the age standard Moldavite P.J. Iunes a , ∗ , G. Bigazzi b , J.C. Hadler Neto a , M.A. Laurenzi b , M.L. Balestrieri b , P. Norelli b , A.M. Osorio Araya c , S. Guedes a , C.A. Tello S. c , S.R. Paulo d , P.A.F.P. Moreira a , R. Palissari a , E.A.C. Curvo a a Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas, UNICAMP, 13083-970, Campinas—SP, Brazil b Istituto di Geoscienze e Georisorse, CNR, Area della Ricerca di Pisa, Via G. Moruzzi 1, 56124 Pisa, Italy c Departamento de Ciências Ambientais, Universidade do Estado de São Paulo, 19060-900 Presidente Prudente—SP, Brazil d Instituto de Ciências Exatas e da Terra, Universidade Federal do Mato Grosso, UFMT, 78070-900 Cuiabá—MT, Brazil Received 13 February 2004; accepted 3 August 2004 Abstract Neutron dosimetry based on U and Th thin films was used for fission-track dating of the age standard Moldavite, the central European tektite, from the Middle Miocene deposit of Jankov (southern Bohemia, Czech Republic). Our fission-track age (13.98 ± 0.58 Ma) agrees with a recent 40 Ar/ 39 Ar age, 14.34 ± 0.04 Ma, based on several determinations on Moldavites from different sediments, including the Jankov deposit. This result indicates that the U and Th thin film neutron dosimetry represents a reliable alternative for an absolute approach in fission-track dating. © 2005 Elsevier Ltd. All rights reserved. Keywords: Fission-track dating; Neutron dosimetry; U thin film; Th thin film; Moldavite 1. Introduction During the last 20 years most fission-track (FT) groups adopted the system calibration known as “zeta calibration” (Hurford and Green, 1983). The use of the zeta calibration, based upon age standards, is a way of overcoming difficul- ties related to uncertainties in the fundamentals (such as in the value of the 238 U spontaneous fission decay constant or in the approach to be adopted for adequate neutron dosime- try) as well as in parameters related to some experimental procedures (such as the external detector method, Gleadow, 1981). However, the zeta calibration makes the FT method ∗ Corresponding author. Fax: +55 193 788 5314. E-mail address: pjiunes@ifi.unicamp.br (P.J. Iunes). 1350-4487/$ - see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2004.08.007 dependent on other isotopic techniques employed for deter- mining the independent reference age of the standards used for the determination of the zeta factor. For this reason, re- search on procedures devoted to enabling FT dating to be an independent system with an absolute calibration was en- couraged (see for instance Hurford, 1998). One of the crucial points for setting an absolute system calibration is neutron dosimetry. Bigazzi et al. (1999) have shown that the use of natural U and Th thin films can be an efficient alternative for accurate neutron dosimetry. In addition, it has been shown that U and Th thin films make possible to apply the FT method also when only weakly thermalized irradiation facilities are available, such as in many research nuclear reactors. The International Union of Geological Sciences (IUGS) had discouraged the use of such facilities (Hurford, 1990), because of the difficulties related