Contribution of the GFR-UAB group to neutron dosimetry and spectrometry C. Domingo, K. Amgarou, T. Bouassoule, M.J. García-Fusté, E. Morales, J. Castelo and F. Fernández Grup de Física de les Radiacions Universitat Autònoma 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 Marín et al. 1998, Radioprotección, S4.71. Fernández 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) Fernández et al. 1988, Radiat. Prot. Dosim., 23, pp Fernández et al. 1991, Nucl. Tracks Radiat. Meas., 19, pp Fernández et al. 1992, Radiat. Prot. Dosim., 44, pp Fernández 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 Vandellòs 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) Fernández et al. 2004, Radiat. Prot. Dosim., 110, pp Fernández et al. 2005, Radiat. Meas., 40, pp García et al., 2005, Radiat. Meas., 40, pp Fernández 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 Ascó 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 Fernández et al. 1997, Radiat. Prot. Dosim., 70, pp Vareille et al. 1997, Radiat. Prot. Dosim., 70, pp Fernández et al. 1998, Radioprotección, 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 Fernández 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 Tomás et al. 2001, Radiat. Prot. Dosim., 110, pp Fernández 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 Fernández et al. 2004, Radiat. Prot. Dosim., 110, pp Gressier et al. 2004, Radiat. Prot. Dosim., 110, pp Fernández et al. 2004, Radiat. Prot. Dosim., 110, pp Domingo et al. 2007, XXXI Bienal RSEF. Fernández et al. 2007, Radiat. Prot. Dosim., 126, pp Fernández et al. 2007, Radiat. Prot. Dosim., 126, pp Fernández et al. 2007, Radiat. Prot. Dosim., 126, pp Fernández 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