(M. Berrondo)
In the last few years we have been studying the problem of designing new scintillator materials for gamma ray and neutron detectors, both theoretically and experimentally. The object of this program is to develop an enhanced understanding of the emission from excited states of specific dopants or other point defects in scintillators, as well as the energy transfer from the crystalline lattice to such centers.
Particularly interesting for our purposes are ionic and partially ionic crystals in which defects such as self-trapped excitons, or specific impurities, such as thallium or cerium, play an active role in the emission process. These are fast processes from allowed transitions, localized around the impurity or defect.
The computational aspects involve modeling the active center of scintillation as an atomic cluster and calculating the electronic structure of the ground state and the excited emmitting state. The presence of f electrons from the rare earth elements - both in the host crystal and as dopants - is especially challenging in our models.
Continuous feeback between theory and experimentation together with a good dose of
serendipity has allowed us to find some new materials for neutron
detection, in spite of the fact that scintillator design is the perfect example of
Murphy's law.