Contribution of the GFR-UAB group to neutron dosimetry and spectrometry C. Domingo, K. Amgarou, T. Bouassoule, M.J. Garca-Fust, E. Morales, J. Castelo and F. Fernndez Grup de Fsica de les Radiacions Universitat Autnoma de Barcelona E Bellaterra (Spain) Overview 1.Introduction 2.Irradiation (Am-Be source) 3.Neutron dosimetry Thermo-luminescent detectors (TLDs) Track detectors Electronic real-time neutron dosemeter 4.Neutron spectrometry Active ( 3 He) and passive ( 197 Au) Bonner sphere systems Monte Carlo simulations of the response functions Neutron spectra unfolding methods 5.Conclusions 6.Perspectives Introduction Origin of neutrons Natural (atmospheric cosmic rays) Artificial (industry, research and medical applications) Broad energy range 10 9 (eV) Introduction Neutron detection Neutrons have neutral charge and complex interaction mechanisms with matter secondary charge particles Detection Ionization of the medium Measurable signals Indirectly ionising radiation: need to estimate the subsequent individual radiological risk Introduction Radioprotection quantities The fluence to dose conversion coefficient is strongly energy dependent Need to determine beforehand the neutron energy spectrum or to have (at least) a priori information about the neutron field characteristics Practical impossibility of building a detector for direct reading of dose, as it would need an energy response curve similar to that of h ICRP publication 75, 1997; ICRU report 57, 1998. Introduction GFR-UAB facilities Detectors TLDs Track detectors (CR-39) Au foils + NaI scintillator Bonner sphere system + 3 He proportional counter + Au foils (activation) Si diodes LIULIN Tools Simulation MCNP and MCNPX GEANT4 Unfolding (spectrometry) MITOM FRUIT Irradiation 1 Ci Am-Be source Irradiator Irradiation Am-Be source Am-Be source 1 Ci activity Container of borated parafin Design of a new irradiator Polyethylene cylinder with central AmBe source, inner lateral holes at different positions and outer boron-loaded paraffin layer. Monte Carlo simulations with MCNPX 2.4.0 Neutron dosimetry TLDs (1990s 2000s) DetectorFilters Observation codeTypeFrontalPosterior 1LiF-6BC n th + + 2LiF-7BC + 3LiF-7AD 4LiF-6AD n albedo + + A = Boron-loaded plastic (3.3 mm) + polypropylene (1.5 mm) B = Polyethylene 8.5 mg/cm 2 C = Boron-loaded plastic (2.9 mm) D = Polypropylene (2.8 mm) Luguera et al. 1990, Radiat. Prot. Dosim., 33, pp Luguera et al. 1996, Radiat. Prot. Dosim., 65, pp Marn et al. 1998, Radioproteccin, S4.71. Fernndez et al. 2004, Radiat. Prot. Dosim., 110, pp Neutron dosimetry Track detectors Etching cells, etching system and reading device was optimised Configuration of the dosemeter. Energy and angular response Intercomparison (EURADOS) Fernndez et al. 1988, Radiat. Prot. Dosim., 23, pp Fernndez et al. 1991, Nucl. Tracks Radiat. Meas., 19, pp Fernndez et al. 1992, Radiat. Prot. Dosim., 44, pp Fernndez et al. 1996, Radiat. Prot. Dosim., 66, pp Bouassoule et al. 1999, Radiat. Prot. Dosim., 85, pp Polyethylene (3mm) Makrofol (300 m ) Air (3mm ) CR 39 (500 m) Methacrylate (5mm ) Phantom (15cm) Neutron dosimetry Track detectors Spectra Measurement Campaign in Vandells II, within a National Coordinated Research Action. Need to improve the dosemeter configuration to adapt it to thermalised neutron spectra present in nuclear industries. Polyethylene (3mm) Makrofol (300 m ) Air (3mm ) CR 39 (500 m) Methacrylate (5mm ) Phantom (15cm) Field Calibration factors Field geometry H p (10,0) * ( Sv)Effective dose ( Sv) PADCAlbedoPADCAlbedo Soft ,06ROT Soft ,04ISO Bare 252 Cf AP 241 Am-Be AP SIGMA ,80AP Field Calibration factors Field geometry H p (10,0) * ( Sv)Effective dose ( Sv) PADCAlbedoPADCAlbedo Soft ,06 ROT Soft ,04ISO Bare 252 Cf AP 241 Am-Be AP SIGMA ,80AP PADC Neutron dosimetry Track detectors Intercomparison exercise with IReS and IPNO Two improved configurations Polyethylene (3mm) Makrofol (300 m) Air (6mm) CR - 39 (500 m) Methacrylate (5mm) Phantom (15cm) Polyethylene (3mm) Makrofol (300 m) Nylon (100 m) CR - 39 (500 m) Methacrylate (5mm) Phantom (15cm) Fernndez et al. 2004, Radiat. Prot. Dosim., 110, pp Fernndez et al. 2005, Radiat. Meas., 40, pp Garca et al., 2005, Radiat. Meas., 40, pp Fernndez et al. 2006, Radioprotection 41, pp. S71-S85. PADC1 PADC2 Now with PADC1 (6mm Air) 290 35 cm -2 mSv -1 Now with PADC2 (100 m Nylon) 592 46 cm -2 mSv -1 Experimental responses to SIGMA source Before with PADC (3mm Air) 130 25 cm -2 mSv -1 Now with PADC1 (6mm Air) 290 35 cm -2 mSv -1 UABIReSIPNO Background50 7 cm 15 cm 21 cm -2 MDDE 52 25 Sv108 46 Sv276 215 Sv Dosemeter responses comparison Background and Minimum Detectable Dose Equivalent comparison PADC2 Dosemeter Neutron dosimetry Track detectors Measurement campaign in Asc I (see poster 233) Participation in the CONRAD exposure at HE neutrons (GSI) PADC2 configuration enclosed in Pb and Cd shells Patient dosimetry in radiotherapy treatments (oral 232, topic 5) Workers dosimetry for density/moisture gauge operators (poster 235) Calibration in quasi-monoenergetic fields (oral 234, topic 4) Domingo et al. 2007, XXXI Bienal RSEF. Silari et al. 2008, Radiat. Meas. In press. Neutron dosimetry Electronic (Si) detectors for real time dosimetry 1990s Double or sandwich diodes Phantom (15 cm) 30 cm Al layer (10 m) Back Si diode (30 m) Si layer (222 m) Front Si diode (30 m) C n H 2n converter (40 m) Al layer (10 m) Air layer (10 m) 1.41 cm Fernndez et al. 1997, Radiat. Prot. Dosim., 70, pp Vareille et al. 1997, Radiat. Prot. Dosim., 70, pp Fernndez et al. 1998, Radioproteccin, S4.64. Neutron dosimetry Electronic (Si) detectors for real time dosimetry Si diode with converters First signal seen at UAB in July 2008 Neutron spectrometry Bonner spheres system Basics A thermal neutron sensitive detector is placed at the centre of each polyethylene sphere of a set having different diameters From the reading M i of each sphere i and once known its response function R i (E), the neutron spectrum is obtained by unfolding the corresponding equation matrix for the whole n spheres used: As the sphere diameter increases the maximum of its sensitivity shifts to high energies Neutron spectrometry The UAB spectrometers 8 polyethylene spheres (diameters: 2.5", 3", 4.2", 5", 6", 8", 10" and 12" inches) of 0.92 g/cm 3 density and a spherical Cd cover (1 mm thick) used with the three smallest ones Active BSS: 3 He proportional counter 3 He(n,p) 3 H counts/channel Channel Passive BSS: Gold activation foils 197 Au(n,p) 198 Au 99.99% purity 15 mm diameter 110 m thick 0.38 g mass Bouassoule et al. 2001, Radiat. Meas., 34, pp Muller et al. 2002, Nucl. Inst. Meth. A, 476, pp Lacoste et al. 2004, Radiat. Prot. Dosim., 110, pp Fernndez et al. 2007, Radiat. Prot. Dosim., 126, pp Bedogni et al. 2007, Radiat. Prot. Dosim., 126, pp Neutron spectrometry Monte Carlo calculation of response functions 3 He BSS (MCNP4B) 197 Au BSS (MCNPX 2.4.0) Neutron spectrometry Unfolding FRUIT unfolding tool Collaboration INFN Frascati Evolution of previous code MITOM Parametric Based on Physics Estimation of all uncertainties User-friendly interface User may operate while unfolding Toms et al. 2001, Radiat. Prot. Dosim., 110, pp Fernndez et al. 2007, Radiat. Prot. Dosim., 126, pp Bedogni et al. 2008, Nucl. Inst. Meth. A, 580, pp Neutron spectrometry Field applications Medical electron LINACs PET cyclotrons Nuclear power plants Fernndez et al. 2004, Radiat. Prot. Dosim., 110, pp Gressier et al. 2004, Radiat. Prot. Dosim., 110, pp Fernndez et al. 2004, Radiat. Prot. Dosim., 110, pp Domingo et al. 2007, XXXI Bienal RSEF. Fernndez et al. 2007, Radiat. Prot. Dosim., 126, pp Fernndez et al. 2007, Radiat. Prot. Dosim., 126, pp Fernndez et al. 2007, Radiat. Prot. Dosim., 126, pp Fernndez et al. 2007, Radiat. Prot. Dosim., 126, pp Conclusions We have presented the current state-of-art of our group with regard to neutron dosimetry and spectrometry. The results of the main research studies made during the last two decades have been outlined, in particular those concerning: The set-up of passive and electronic real-time personal neutron dosimeters The experimental and theoretical characterization of two Bonner sphere systems based on 3 He proportional counter and gold foil ( 197 Au) activation detector as well as their application in several field measurements The development of neutron spectra unfolding techniques Expertise in Monte Carlo simulations of neutron production, transport and detection Perspectives The main motivation of our group is to broaden the necessary knowledge and resources in order to respond, at mid term, to the increasing demand in our country in which respects to an experimental reference laboratory for neutron dosimetry and spectrometry The range of application of the active and passive BSSs is extended to high-energy neutrons (>20 MeV) by adding several spheres with inner metallic (Pb and Cu) shells. These new systems will be of great utility to characterize the neutron spectra at high-energy particle accelerators and cyclotrons as well as those induced by atmospheric cosmic rays at different altitudes or during large duration transoceanic flights