Polysiloxane based neutron detectors

In the last decade, neutron detection has been attracting the attention of the scientific community for different reasons. On one side, the increase in the price of 3He, employed in the most efficient and the most widely used neutron detectors. On the other side, the harmfulness of traditional xylene based liquid scintillators, used in extremely large volumes for the detection of fast neutrons. Finally, the demand for most compact and rough systems pushed by the increased popularity of neutron imaging, neutron scattering and neutron diffraction techniques. Polysiloxanes could help addressing some of the existing issues regarding neutron detection thanks to their unique properties. For this reason, in this work, polysiloxane scintillators have been developed and characterized, with a special attention to their optical properties and their time response. In particular, this thesis describes the investigation of the scintillation performances of several different polysiloxane liquids. The results have been connected with the optical properties of the material, in turns linked to its molecular structure, allowing to select the most suitable polysiloxane solvent for liquid scintillators. The timing properties of scintillating mixtures employing the best performing polysiloxane solvent were consequently analyzed as a function of the primary dye concentration, with a special focus to the pulse shape discrimination (PSD) capability of the material. PSD is indeed one of the most important characteristic of liquid scintillators, and one of the factors determining their large use. Beside polysiloxane liquids, time response of polysiloxane plastic scintillators was also investigated with the aim of studying their PSD capability. At the moment, indeed, only few examples of plastic scintillators capable of PSD exist, and also in those cases some criticalities emerged connected with stability issues and efficiency. Production of red emitting polysiloxane plastic scintillators is also described in this work, analyzing the energy transfer process between dyes in order to optimize the readout with an avalanche photodiode. This would allow overcoming some issues connected with the use of photomultiplier tubes, in more compact and rugged systems. Finally some preliminary results about the HYDE experiment are presented. This project aims at the development of a hybrid detector for neutrons, combining a 3D silicon diode with a suitable neutron converter, in order to produce a compact efficient neutron detector with good spatial resolution. With this goal different types of converters for fast and thermal neutrons were tested and the performances of 3D and planar devices were compared.