Applied Radiation and Isotopes 61 (2004) 1021–1026 Measurement of free beam neutron spectra at eight BNCT facilities worldwide I. Auterinen a, *,T.Sere´n a , K. Anttila a , A. Kosunen b , S. Savolainen c,d a VTT Processes, POB 1608, FIN-02044 VTT, Finland b Radiation Metrology Laboratory, Radiation and Nuclear Safety Authority-STUK, POB 14, FIN-00881 Helsinki, Finland c Department of Physical Sciences, University of Helsinki, POB 64, FIN-00014 Finland d Helsinki Medical Imaging Center, University of Helsinki, P.O. Box 340, FIN-00029 HUS, Finland Abstract Eight epithermal neutron beams, constructed for clinical or preclinical studies of NCT, have been dosimetrically characterizedbyin-airmeasurementswithasetofactivationfoilsforthedeterminationoftheneutronenergyspectrain free beam. Measurements have been made on the already closed epithermal BNCT facility at the BMRR of the Brookhaven National Laboratory, on the HFR at JRC in Petten, The Netherlands, on the epithermal mode beam at KURRI,Japan,onthefissionconverterbeamatMIT,USA,ontheepithermalbeamoftheRA-6facilityinBariloche, Argentina,ontheepithermalbeamatWSU,USA,onthemixedmodebeamatJRR-4atJAERI,Japan,aswellason the epithermal beam at FiR 1 at VTT, Espoo, Finland. r 2004 Elsevier Ltd. All rights reserved. Keywords: BNCT; Epithermal neutron beam; Neutron spectrum; Activation detectors 1. Introduction In 2000 on the initiative of Professor Otto Harling from MIT (USA) a project called ‘‘International Dosimetry Exchange’’ was started (Harling et al., 2002).Themainfocusofthisinitiativeisthecomparison of the physical dosimetry of all neutron beams used for clinicalstudiesinBNCT.Theworkisbasedonboththe dosimetric methods developed locally at each centre as well as on the common guidelines created in the European project for a Code of Practice for dosimetry of boron neutron capture therapy in Europe (Stecher- Rasmussenetal.,1997; VoorbraakandJa¨rvinen,2003). Theobjectiveofneutronbeamspectrumcharacterisa- tionisthesourcetermvalidationandthedetermination ofbeamenergyparametersneededforthemeasurement of the relevant dosimetric quantities, like neutron dose. A validated neutron source term is needed as an input forthetreatmentplanningcalculations.Thesourceterm is obtained by computer calculations taking into account the geometrical arrangement and the material composition of the beam-limiting device as precisely as possible. The spectral source term determined by calculations is adjusted by experimental data. One of the tasks of the dosimetry group from VTT wastodeterminetheneutronspectruminBNCTbeams using the multifoil activation detector method (see e.g. ASTME721-94,1998; ASTME944-96,1998).Already before this project the Finnish BNCT facility had performed some dosimetry exchange with BNL, USA in collaboration with the INEEL, USA (Nigg et al., 1999; Sere´n et al., 1999), with the KURRI, Japan and with the Petten BNCT facility within the European project mentioned above. In the International Dosime- tryExchangeprojectadditionallytheBNCTfacilitiesat MIT, USA (new fission converter beam, FCB), at ARTICLE IN PRESS *Corresponding author. Tel.: +358-9-456-6353; fax: +358- 9-456-6390. E-mail address: Iiro.Auterinen@vtt.fi (I. Auterinen). 0969-8043/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2004.05.035