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Contribution of the GFR-UAB group to neutron dosimetry and spectrometry

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-08193 Bellaterra (Spain). Overview. Introduction

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Contribution of the GFR-UAB group to neutron dosimetry and spectrometry

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  1. 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-08193 Bellaterra (Spain)

  2. Overview • Introduction • Irradiation (Am-Be source) • Neutron dosimetry • Thermo-luminescent detectors (TLDs) • Track detectors • Electronic real-time neutron dosemeter • Neutron spectrometry • Active (3He) and passive (197Au) Bonner sphere systems • Monte Carlo simulations of the response functions • Neutron spectra unfolding methods • Conclusions • Perspectives

  3. IntroductionOrigin of neutrons • Natural (atmospheric cosmic rays) • Artificial (industry, research and medical applications) Broad energy range 10-3 – 109 (eV)

  4. IntroductionNeutron detection • Neutrons have neutral charge and complex interaction mechanisms with matter Detection secondary charge particles Measurable signals Ionization of the medium Indirectly ionising radiation: need to estimate the subsequent individual radiological risk

  5. IntroductionRadioprotection 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 hF ICRP publication 75, 1997; ICRU report 57, 1998.

  6. Detectors TLDs Track detectors (CR-39) Au foils + NaI scintillator Bonner sphere system + 3He 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 IntroductionGFR-UAB facilities

  7. IrradiationAm-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

  8. Neutron dosimetryTLDs (1990s – 2000s) Luguera et al. 1990, Radiat. Prot. Dosim., 33, pp. 207-209. Luguera et al. 1996, Radiat. Prot. Dosim., 65, pp. 321-324. Marín et al. 1998, Radioprotección, S4.71. Fernández et al. 2004, Radiat. Prot. Dosim., 110, pp. 701-704. A = Boron-loaded plastic (3.3 mm) + polypropylene (1.5 mm) B = Polyethylene 8.5 mg/cm2 C = Boron-loaded plastic (2.9 mm) D = Polypropylene (2.8 mm)

  9. neutrons Polyethylene (3mm) Makrofol (300mm) Air (3mm) CR – 39 (500mm) Methacrylate (5mm) Phantom (15cm) Neutron dosimetryTrack detectors • 1988-1999 • 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. 175-178. Fernández et al. 1991, Nucl. Tracks Radiat. Meas., 19, pp. 467-470. Fernández et al. 1992, Radiat. Prot. Dosim., 44, pp. 337-340. Fernández et al. 1996, Radiat. Prot. Dosim., 66, pp. 343-347. Bouassoule et al. 1999, Radiat. Prot. Dosim., 85, pp. 39-43.

  10. neutrons Polyethylene (3mm) Makrofol (300mm) Air (3mm) CR – 39 (500mm) Methacrylate (5mm) Phantom (15cm) Neutron dosimetryTrack detectors • 2000-2002 • 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. PADC

  11. Now with PADC1 (6mm Air) Now with PADC1 (6mm Air) Before with PADC (3mm Air) neutrons neutrons Polyethylene (3mm) Polyethylene (3mm) 290 ± 35 cm-2mSv-1 290 ± 35 cm-2mSv-1 Makrofol (300mm) Makrofol (300mm) 130 ± 25 cm-2mSv-1 Now with PADC2 (100mm Nylon) Air (6mm) Nylon (100mm) CR - 39 (500mm) CR - 39 (500mm) Methacrylate (5mm) Methacrylate (5mm) 592 ± 46 cm-2mSv-1 Phantom (15cm) Phantom (15cm) Neutron dosimetryTrack detectors Fernández et al. 2004, Radiat. Prot. Dosim., 110, pp. 701-704. Fernández et al. 2005, Radiat. Meas., 40, pp. 601-606. García et al., 2005, Radiat. Meas., 40, pp. 607-611. Fernández et al. 2006, Radioprotection 41, pp. S71-S85. • 2003-2004 • Intercomparison exercise with IReS and IPNO PADC2 Dosemeter Experimental responses to SIGMA source Two improved configurations • Dosemeter responses comparison • Background and Minimum Detectable Dose Equivalent comparison PADC1 PADC2

  12. Neutron dosimetryTrack detectors • 2004-2008 • 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.

  13. 1.41 cm Air layer (10 mm) Al layer (10 mm) CnH2n converter (40 mm) Front Si diode (30 mm) Si layer (222 mm) Back Si diode (30 mm) Al layer (10 mm) Phantom (15 cm) 30 cm Neutron dosimetryElectronic (Si) detectors for real time dosimetry • 1990s • Double or sandwich diodes Fernández et al. 1997, Radiat. Prot. Dosim., 70, pp. 87-92. Vareille et al. 1997, Radiat. Prot. Dosim., 70, pp. 79-82. Fernández et al. 1998, Radioprotección, S4.64.

  14. Neutron dosimetryElectronic (Si) detectors for real time dosimetry • 2007-2008 • Si diode with converters First signal seen at UAB in July 2008

  15. Neutron spectrometryBonner 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 Mi of each sphere i and once known its response function Ri(E), the neutron spectrum is obtained by unfolding the corresponding equation matrix for the whole n spheres used: the maximum of its sensitivity shifts to high energies As the sphere diameter increases

  16. Active BSS: 3He proportional counter 3He(n,p)3H 60 Passive BSS: Gold activation foils 197Au(n,p)198Au 50 counts/channel 40 99.99% purity 15 mm diameter 110 mm thick 0.38 g mass 30 20 10 0 0 200 400 600 800 1000 1200 1400 1600 Channel Neutron spectrometryThe UAB spectrometers 8 polyethylene spheres (diameters: 2.5", 3", 4.2", 5", 6", 8", 10" and 12" inches) of 0.92 g/cm3 density and a spherical Cd cover (1 mm thick) used with the three smallest ones Bouassoule et al. 2001, Radiat. Meas., 34, pp. 199-202. Muller et al. 2002, Nucl. Inst. Meth. A, 476, pp. 411-415. Lacoste et al. 2004, Radiat. Prot. Dosim., 110, pp. 529-532. Fernández et al. 2007, Radiat. Prot. Dosim., 126, pp. 366-370. Bedogni et al. 2007, Radiat. Prot. Dosim., 126, pp. 342-345.

  17. 197Au BSS (MCNPX 2.4.0) 3He BSS (MCNP4B) Neutron spectrometryMonte Carlo calculation of response functions

  18. Neutron spectrometryUnfolding Tomás et al. 2001, Radiat. Prot. Dosim., 110, pp. 545-548. Fernández et al. 2007, Radiat. Prot. Dosim., 126, pp. 361-365. Bedogni et al. 2008, Nucl. Inst. Meth. A, 580, pp. 1301-1309. • 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

  19. Neutron spectrometryField applications PET cyclotrons Medical electron LINACs Nuclear power plants Fernández et al. 2004, Radiat. Prot. Dosim., 110, pp. 517-521. Gressier et al. 2004, Radiat. Prot. Dosim., 110, pp. 523-527. Fernández et al. 2004, Radiat. Prot. Dosim., 110, pp. 517-521. Domingo et al. 2007, XXXI Bienal RSEF. Fernández et al. 2007, Radiat. Prot. Dosim., 126, pp. 355-360. Fernández et al. 2007, Radiat. Prot. Dosim., 126, pp. 361-365. Fernández et al. 2007, Radiat. Prot. Dosim., 126, pp. 366-370. Fernández et al. 2007, Radiat. Prot. Dosim., 126, pp. 371-375.

  20. 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 3He proportional counter and gold foil (197Au) 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

  21. 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

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