Organic Scintillators for Neutrons Alberto Quaranta Laboratori Nazionali

Organic Scintillators for Neutrons Alberto Quaranta Laboratori Nazionali di Legnaro - INFN University of Trento – Dept. Materials Engineering Ind. Technologies (DIMTI)

Scintillators for thermal neutrons are based on the detection of the reaction products between neutrons and few nucleus which can be dispersed in the scintillating matrix.

Scintillators for thermal neutrons Liquid scintillators: high efficiency, pulse shape for n-g discrimination. Toxic, corrosive, flammable, explosive. . . Inorganic scintillators: high radiation hardness Cryst. growth technology, pressed unhomogenous powders. Plastic scintillators: different shapes and volumes Low radiation resistance. New polymers have to be studied.

Needs of new scintillators for neutrons Neutron counting and monitoring. Complex geometries and high volumes.

State of art Commercial plastic scintillators. BC-454/EJ-245 (B). 14 €/g for B containing. Carborane as boron disperser in PS Volatile, not always soluble and 100 €/g. Plastic and microcrystal mixed scintillators. Unhomogeneous. Gd and B containing silicone rubbers. Studies are still at a preliminar stage (Oak-Ridge).

ORIONE – ORganic sc. Intillators for NEutrons LNL – LNS The aim of ORIONE experiment is develop rubber scintillators for the detection of thermal neutrons. Selection of the luminescent silicone rubber matrix. Selection of the luminescent dye molecule converting in light the excited states of the matrix. Selection of a suitable organic compound containing the reactive nucleus.

Why silicone rubbers? Dimethyl-diphenyl-polysiloxane Good radiation hardness. Thermal stability (-55 up to 290 °C) and workability (easy to cut and to handle). Fluorescence by varying and refractive index can be tailored the amount of diphenyl groups. 3 -D cross linking can be attained to improve the radiation hardness.

Preirradiation PS irradiated in air Transmittance After 3 Mrads Preirradiation Transmittance 600 Ci 60 Co source SR irradiated in air After 18 Mrads 600 Ci 60 Co source M. Bowen et al. IEEE Trans. Nucl. Sci. 36 (1989) 562

Suited dye molecules Overlap between dye absorption spectrum and polymer fluorescence spectrum. Good solubility in the polymer matrix. Good radiation hardness. 2, 5 diphenyloxazole - PPO

Preliminary tests Photoluminescence and radioluminescence measurements on silicone rubber doped with only PPO show the dye emission band as the main luminescence feature.

Preliminary tests Pulse height spectra show a higher light yield of silicone doped scintillator (1% PPO) with respect to NE 102 under excitation with a particles.

2009 planned activity New organic compounds for dispersing Gd and B in the silicone polymer. Gadolinium and Boron compounds requirements Highly soluble in the siloxane fluids. Inert to the cross-linking reaction and to the light yield. Thermally resistant (up to 100°C, final annealing for the cross-linking completion).

2009 planned activity Test on the radiation hardness of the silicone scintillators (crosslinking as an improvement). Scintillation degradation during ion irradiation. Formation of color centers after exposure to the “Gamma Knife” 60 Co source at LNS (3 Gy/min). Test on the effect of the compounds on the scintillation yield and pulse shape. a and g radiation sources and ion beams at LNL and LNS.

2009 planned activity First scintillation tests with neutrons. LNS neutron converter Graphite cylinder + lead shield for gamma background + PEHD for moderating the neutrons. After the preparation of the neutron converter the first n detection tests will be performed at LNS.

Planned activity 2010 Full characterization for n detection capabilities of the produced scintillators. Pulse shape and height analyses for studying the capabilitiels for n-g discrimination.

Staff Nat. Resp. Alberto Quaranta LNL Resp. Sara Carturan Fabiana Gramegna Vladimir Kravchuk Gianantonio Della Mea Michele Tonezzer Gabrio Valotto Sandro Sassi Mauro Masiol LNS Resp. Maurizio Re Giacomo Cuttone Gianluigi Cosentino Alfio Pappalardo

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