Speaker
Description
Among the radiation effects to detector and electronic components, the displacement damage due to neutron exposure is a key aspect. At ELBE an optimal neutron radiation source for radiation hardness studies is provided at the pELBE beamline at the ELBE Positron Source facility (EPOS), as secondary radiation with unique properties. The heart of EPOS is a 1 cm W target, which not only induces bremsstrahlung and then pair production in view of the positron selection, but is also, de facto, a photo-neutron source. This source provides a neutron field optimal for radiation hardness studies, due to the typical photo-production spectrum (which is peaked at 1 MeV), the high neutron fluence rate (up to 107 n per cm2 per second), and the negligible contamination due to the optimal shielding to the photon field provided by the lead cage.
Until now the neutron irradiation area at the EPOS facility has been characterized only via Monte Carlo simulations. With the aim to validate the Monte Carlo results, and to perform an accurate calibration of the area in view of future irradiation campaigns, a spectral characterization with a Bonner Sphere Spectrometer (BSS) has been performed. The Bonner Sphere Spectrometer of INFN Frascati National Laboratories, which consists of a set of 13 polyethylene spheres inside of which a Li6I(Eu) scintillator is inserted, was used.
Considering the EPOS neutron spectrum, a set of 9 spheres with diameter ranging from 2 in to 8 inches, adequate to cover the full energy range, was considered. The complete characterization was performed for three different points placed on the nELBE lead roof under the same irradiation conditions, which consists in the use of a 34 MeV electron beam whit a mean current of 2 nA, corresponding to 3x105 n/cm2/s estimated in the points of interest. Once obtained the counts for the entire set for each point considered and exploiting the knowledge of the response matrix, the unknown neutron field has been estimated using the default spectrum, produced through a Bayesian approach, and then the unfolding code UMG (MAXED and GRAVEL packages).
| Scientific Topic 3 | Code benchmarking and intercomparison |
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