Ponente
Descripción
Scintillator-based detection systems are in wide use since many years and in many applications ranging from nuclear and particle physics experiments to medical imaging and security. Their physical properties like density, light yield, linearity of the detector response and operational speed, but also their resistance to harsh radiation load, their insensitivity to small changes in operational parameters and the widely available production capabilities, make them one of the
most popular devices for the detection and the energy measurement of charged and neutral particles interacting with material structures.
The timing resolution of scintillators is to first order proportional to the square root of the photon density (number of produced photons per time interval), which can itself be expressed as the ratio of the emission decay time and the light yield of the scintillator. Therefore, to minimise timing resolution, scintillator development aims at achieving a maximum light yield with the shortest possible decay times.
Conventional commonly used scintillators produce an amount of light proportional to the energy deposited by charged or neutral particles. The energy transfer from initial ionisation in the bulk material to the luminescence centres is complex and leads to an intrinsic time-resolution limit in photoproduction due to the stochastic relaxation processes of the hot electron-hole pairs produced by the impact of radiation on the crystal material. To go below this intrinsic limitation,
various ways of exploiting faster photon production mechanisms have been investigated, among which the development of semiconductor nanomaterials represents a promising route towards fast timing. In direct-band-gap-engineered semiconductor nanostructures, one effect of quantum confinement consists of a significant enhancement of Coulomb interactions between charge carriers of electron-hole pairs, coherent and multiexciton states. This plays a significant role in enhancing the transition dipole moment of absorption and emission and can thus increase the rate of fast radiative transitions resulting in scintillation decay times below 1 ns.
Several types of scintillating nanomaterials with different levels of confinement (nanoplatelet, quantum wire, quantum dots) have been studied over many years, reaching a fast photon emission with characteristic radiative decay times in the range of nanosecond or sub-nanosecond. The very short decay times of such nanocrystals together with the possibility to tune their emission spectra open new prospects for timing detectors for particle physics experiments, such as precision timing layers for time tagging of collision tracks or scintillators for the energy measurement of particles in combination with high time resolution.
Hetero-structured scintillations obtained by the growth of new fast scintillators, e.g., nanoparticle 2D perovskites over a heavy scintillator component, like Bismuth Germanate (Bi4Ge3O12) BGO, will allow to use the system as an active stopper for decay experiments of rare isotopes. This system allows to stop and detect at the same time beta-decaying exotic radioactive nuclei, measuring electrons, neutrons (through 6Li film converter) and gamma rays in the same detector, having good electron-detection efficiency, gamma capture (stopping power) and scintillation performance (ultra-fast and high light yield emission).
In this talk, first results based on BaZrO3 perovskites will be presented, together with prospects for using further materials as A4SnX4 chalcogenide family compounds with optical properties very similar to GaAs.
