Monte Carlo calculations and validation of a gold foil-based Bonner sphere system

Abstract

The Grup de Física de les Radiacions (GFR) of the Universitat Autònoma de Barcelona (UAB), in collaboration with the Institute for Radiological Protection and Nuclear Safety (IRSN), has developed a passive Bonner sphere system (UAB-BSS), with gold foils as thermal neutron detectors, for application in pulsed neutron fields or in mixed neutron-photon fields with high photon intensities. In such fields, active devices suffer from saturation and dead-time effects. The MCNPX Monte-Carlo code has been used to determine the response to neutrons of different energies of each polyethylene sphere belonging to the BSS. The passive UAB-BSS system was characterised with the ISO (252)Cf reference source at the IRSN facilities. The energy distribution of the reference source neutron fluence was folded with the response functions for comparison with the experimental data. A good agreement between the experimental and calculated count rates was found.

Response functions of a Bonner sphere spectrometer calculated with GEANT4

“…[17]. The diameters of the (white) PE spheres with density r ¼ 0:95 g=cm 3 were 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6,7,8,9,10,11,12,15 in., respectively. The inner black sphere with density r ¼ 0:96 g=cm 3 and diameter 1.3 in.…”

“…Depending on the fluence rate of the neutron field, different thermal neutron detectors are used. So-called ''active'' detectors such as 3 He-proportional counters [5][6][7][8], are used at low neutron fluence rates while so-called ''passive'' and less sensitive detectors such as gold foils [9][10][11][12][13][14][15], are preferred to measure high neutron fluence rates. For example, 3 He-counters are presently being used for continuous measurements of secondary neutrons from cosmic radiation at mountain altitude or in Spitsbergen [7,16].…”

“…For example, 3 He-counters are presently being used for continuous measurements of secondary neutrons from cosmic radiation at mountain altitude or in Spitsbergen [7,16]. In contrast, at high neutron fluence rates, such as those that might occur at nuclear facilities, the less sensitive gold foils are preferred [11][12][13][14]. For example, a BSS system including gold foils as detectors has recently been used to detect the neutrons at the MEDAPP neutron therapy facility at the FRM II in Garching, Germany [17,18].…”

Design and experimental validation of a Bonner Sphere Spectrometer based on Dysprosium activation foils

“…In a recent work, based on 15 mm diameter and 0.1 mm thick gold foils inside a BSS (Fernández et al, 2007), extensive Monte Carlo simulations were done to investigate the response of the BSS when the orientation of the foil is varied with respect to the incident beam. The anisotropy effects, seen for small spheres and for energies where the sphere response is low, were found to be comparable with the expected overall uncertainty of the BSS response matrix (2e3%).…”

“…TLD pairs (Barquero et al, 2005;Howell et al, 2005;Bedogni et al, 2008a) or gold activation foils (Thomas et al, 2007;Fernández et al, 2007;Bedogni et al, 2008b) have been frequently used as central detectors for passive BSS. Whilst TLDs are in general more sensitive, gold foils are most suited for workplaces with high photon component because of their insensitivity to photons.…”