27 September 2011 Towards an understanding of nonlinearity in scintillator detector materials
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Abstract
It has been known for more than 50 years that the light emitted by a scintillator under high-energy excitation (gamma, alpha, proton) is not always proportional to the amount of absorbed energy. The deviation from the linearity of luminosity versus absorbed energy is known as nonproportionality. In addition to its academic interest, this phenomenon has been considered central for scintillator development due to its implication in the limitation of achievable detector performance. Although non-proportional response was studied intensively during the second part of the 20th century, the understanding of its origin and implications on scintillator performance are mainly qualitative. Research in the 1960s uncovered a correlation between proportional response and ionization density, while in the 1980s nonproportionality was proposed as the main reason of energy resolution deviation from the counting statistics limit. It is only recently that the bridge between qualitative and quantitative understanding has been crossed, mainly driven by the large effort undertaken to discover new high-resolution scintillators. Developing such detector materials prompted efforts to gain a deeper understanding of the microscopic processes involved in scintillation mechanisms and so in nonproportionality. In this manuscript, the phenomenology of past and present understanding of non-proportional response will be reviewed. Based on recent experimental, computational and theoretical works, the relation between nonlinear response and energy resolution degradation will be addressed. Finally, the relation between material parameters and proportionality will be evaluated. These recent works are leading towards a deeper understanding of nonlinearity in scintillator detector materials and should result in the development of new high performance scintillator materials.
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G. Bizarri, W. W. Moses, S. A. Payne, R. T. Williams, "Towards an understanding of nonlinearity in scintillator detector materials", Proc. SPIE 8142, Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XIII, 81420X (27 September 2011); doi: 10.1117/12.896001; https://doi.org/10.1117/12.896001
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