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During the last decade much effort has been devoted in the synthesis of radiation resistant siloxane based scintillators doped with primary dye and wavelength shifter to detect with good light output both γ-rays and α particles [1-3]. Moreover, liquid siloxane based scintillating cocktails have been prepared and recently tested as for fast neutrons detection and n-γ discrimination [4]. The detection of thermal neutrons using boron loaded siloxane scintillator has been also pursued, by using soluble compounds of boron, such as carborane, dissolved in the precursor resins prior to the cross-linking reaction [5]. Quite recently, 6LiF nanoparticles have been synthesized and entrapped in siloxane based scintillators and thermal neutrons have been detected, owing to the capture reaction leading to α and triton ionizing particles [6]. Good performances have been recorded both using boron or lithium compounds dispersed into the doped polymer matrix, though the light output is much lower than ZnS:Ag based standard detector, one of the most popular thermal neutrons detector. The commercial plate for thermal neutrons is based on a mixture of the inorganic phosphor ZnS:Ag, which is known to display extremely high light output (around 50 photons/KeV), and micron-sized particles of 6LiF as thermal neutron sensitizer. The mixture is added with a small amount of polymeric binder and pressed on an acrylic disk acting both as a light guide and as a support, since the composite as a self-supporting film is very fragile. The mean free path of both the generated particles inside the 6LiF grain, alpha and triton, resulting from the capture reaction 6Li (n,α) 3H is in the order of some microns (around 30 µm and 6 µm for triton and alpha respectively). Therefore, the grain size of the 6LiF powder used as absorber is a crucial parameter and the entrapment of 6LiF nanoparticles into the composite could lead to greatly improved light output, owing to the increased interaction of ionizing particles with the surrounding light emitting phosphor. On the other hand, the entrapment of the mixture in elastomeric binders such as radiation hard polysiloxane allows the production of flexible thermal neutron detectors, with remarkable advantages on their application to different fields. In this work, the preparation of 6LiF nanocrystals has been pursued by co-precipitation technique, using a mixture of water and ethanol in different ratios. The as-prepared nanocrystals have been characterized as for crystal structure and crystallites size by X-Ray Diffraction (XRD), whereas the composition has been investigated by Energy Dispersive Spectroscopy (EDS). In this preliminary step towards the realization of a new detector, the commercial inorganic phosphor ZnS:Ag (EJ-600) has been used as scintillating medium. A fixed weight ratio of 6LiF nanocrystals and EJ600 phosphor has been chosen, namely 3:1 EJ-600:6LiF, whereas different amounts of the mixture have been added to the polysiloxane binder, prior to cross-linking. The composites have been benchmarked as for light output and thermal neutrons detection efficiency against a commercial sample of EJ-426 taken as a reference.
[1] A. Quaranta et al., IEEE TNS Nucl. Sci. 57 (2010) 891.
[2] A. Quaranta et al., Opt. Mat. 32 (2010) 1317.
[3] A. Quaranta et al., Mat. Chem. Phys. 137 (2013) 951.
[4] M. Dalla Palma et al., IEEE TNS Nucl. Sci. 63 (2016) 1608.
[5] S. Carturan et al., Rad. Prot. Dos. 143 (2011) 471.
[6] S. Carturan et al., J. Phys.: Conf. Ser. 620 (2015) 012010.
