Radiation Measurements 43 (2008) 1113 – 1117 www.elsevier.com/locate/radmeas Determination of workplace neutron spectra at a high energy hadron accelerator using active and passive Bonner sphere spectrometers R. Bedogni ∗ , A. Esposito, M. Chiti INFN–LNF Frascati National Laboratory, Via E. Fermi n. 40, 00044 Frascati, Italy Abstract In the framework of the 2006 experimental benchmark organized at the GSI (Darmstadt, Germany) by the EC CONRAD network, a neutron dosimetry intercomparison was performed in a workplace field around a carbon target hit by 400 MeV/u 12 C ions. The radiation protection group of the INFN-LNF participated to the intercomparison with a Bonner sphere spectrometer equipped with an active 6 LiI(Eu) scintillator and a set of passive detectors, namely MCP-6s (80 mg cm -2 )/MCP-7 TLD pairs from TLD Poland. Both active and passive spectrometers, independently tested and calibrated, were used to determine the field and dosimetric quantities in the measurement point. The FRUIT unfolding code, developed at the INFN-LNF radiation protection group, was used to unfold the raw BSS data. This paper compares the results of the active or passive spectrometers, obtaining a satisfactory agreement in terms of both spectrum shape and value of the integral quantities, as the neutron fluence or the ambient dose equivalent. These results allow qualifying the BSS based on TLD pairs as a reliable passive method to be used around high energy particle accelerators even in low dose rate areas. This is particularly useful in those workplaces where the active instruments could be disturbed by the presence of pulsed fields, large photon fluence or electromagnetic noise. © 2007 Elsevier Ltd. All rights reserved. Keywords: Bonner spheres; Neutron spectrometry; TLD pairs; High energy neutrons 1. Introduction The European Commission (EC) is funding a three years (2005–2007) project, CONRAD, (COordinated Network for RAdiation Dosimetry), which includes a work package (WP6, complex mixed radiation fields) devoted to the characterization of workplace fields as those encountered at high energy parti- cle facilities (Silari, 2006). In this framework, an experimental dosimetry and spectrometry benchmark was organized at the GSI (Darmstadt, Germany). Here, in the so-called “Cave A”, a high energy mixed neutron/photon field is produced behind the thick concrete shield of a graphite target (10 cm × 10 cm × 20 cm) hit by 400 MeV/u 12 C ions. Among other experimen- tal groups, the INFN-LNF Radiation Protection Group partic- ipated with a commercial Bonner sphere spectrometer (BSS) equipped with an active 4 mm × 4 mm 6 LiI(Eu) scintillator and a series of specially designed TLD pairs. An additional sphere ∗ Corresponding author. Tel.: +39 0694032608; fax: +39 0694032364. E-mail address: roberto.bedogni@lnf.infn.it (R. Bedogni). 1350-4487/$ - see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2007.10.011 with a 1 cm internal lead shell was used to derive information on the high energy neutron component. Active BSSs equipped with metal shells are a well- established method for the characterization of neutron fields with a significant high energy component (Vylet et al., 1997; Wiegel and Alevra, 2002). Nevertheless, active devices could not be suited for some areas of high energy facilities where the presence of pulsed fields, very intense photon component and electromagnetic noise could disturb their operation. In addition, the need of electric supply could be a problem in the use of active BSSs in certain workplaces. Passive BSSs based on TLD-600 and TLD-700 pairs have been already used, but the low sensitivity of these detectors limited their application to workplaces characterized by high fluence rate, as medical LINACs (Barquero et al., 2005) or nuclear reactors (Sweezy et al., 1998). This system was also used in fields with an important high energy component, such as the cosmic rays field (Vega-Carrillo and Mazanares-Acuña, 2004; Hajek et al., 2002), but large integration time (months) was required, and the use of pure polyethylene spheres