Abstract
Neutrons are known to be unique probes in situations where other types of radiation fail to penetrate samples and their surrounding structures. In this paper it is demonstrated how thermal and cold neutron radiography can provide time-resolved imaging of materials while they are being processed (e.g. while growing single crystals). The processing equipment, in this case furnaces, and the scintillator materials are opaque to conventional X-ray interrogation techniques. The distribution of the europium activator within a BaBrCl:Eu scintillator (0.1 and 0.5% nominal doping concentrations per mole) is studied in situ during the melting and solidification processes with a temporal resolution of 5-7 s. The strong tendency of the Eu dopant to segregate during the solidification process is observed in repeated cycles, with Eu forming clusters on multiple length scales (only for clusters larger than ∼50 µm, as limited by the resolution of the present experiments). It is also demonstrated that the dopant concentration can be quantified even for very low concentration levels (∼0.1%) in 10 mm thick samples. The interface between the solid and liquid phases can also be imaged, provided there is a sufficient change in concentration of one of the elements with a sufficient neutron attenuation cross section. Tomographic imaging of the BaBrCl:0.1%Eu sample reveals a strong correlation between crystal fractures and Eu-deficient clusters. The results of these experiments demonstrate the unique capabilities of neutron imaging for in situ diagnostics and the optimization of crystal-growth procedures.
Highlights
While multiple novel scintillation materials have been discovered during the past decade (Cherepy et al, 2008; Derenzo et al, 2003; Combes et al, 1999; Bourret-Courchesne et al, 2009, 2010, 2012; Yang et al, 2011; Tyagi et al, 2013; Nikl & Yoshikawa, 2015), only a couple of them have made a successful transition to commercialization
Despite the relatively high penetration of neutrons for many -ray scintillation materials, obviously not all of them can be studied by white-beam neutron imaging for either of two reasons: (i) Some specific elements, such as Gd, Cd, 10B and 6Li, are strong neutron absorbers and can only be studied either with thin samples or when these elements or isotopes have a low concentration within the material composition
Tremsin et al Neutron imaging of crystal growth is observed from variation of the elemental composition or the presence of defects
Summary
While multiple novel scintillation materials have been discovered during the past decade (Cherepy et al, 2008; Derenzo et al, 2003; Combes et al, 1999; Bourret-Courchesne et al, 2009, 2010, 2012; Yang et al, 2011; Tyagi et al, 2013; Nikl & Yoshikawa, 2015), only a couple of them have made a successful transition to commercialization. This transition is extremely time consuming and usually requires many years of development in order to optimize the raw material purification process and crystal-growth procedures to the industrial scale. These must be obtained reproducibly in high yield, with a relatively large size and at a low cost of production
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