Lyoluminescence

Lyoluminescence refers to the emission of light while dissolving a solid into a liquid solvent. It is a form of chemiluminescence. The most common lyoluminescent effect is seen when solid samples which have been heavily irradiated by ionizing radiation are dissolved in water. The total amount of light emitted by the material increases proportionally with the total radiation dose received by the material up to a certain level called the saturation value.

Recent investigations have been directed toward applications to dosimetry, particularly at high doses. Both organic and inorganic phosphors exhibit the property, but the mechanism for light emission is different in detail for the two classes of materials.

Many gamma-irradiated substances are known to lyoluminescence; these include spices, powdered milk, soups, cotton and paper. While the broad variety of materials which exhibit lyoluminescence confounds explanation by a single common mechanism there is a common feature to the phenomenon, the production of free radicals in solution. Lyoluminescence intensity can be increased by performing the dissolution of the solid in a solution containing conventionally chemiluminescent compounds such as luminol. These are thus called lyoluminescence sensitizers.

A large range of organic materials exhibit lyoluminescence, among the more sensitive of which are monosaccharides and amino acids. A dose response curve for mannose (C6H12O6) and an example of lyoluminescence apparatus are illustrated. The principle advantage of lyoluminescence dosimetry is that lyoluminescent phosphors may be used which closely approximate the chemical composition of tissue. Therefore all radiation fields KERMA (kinetic energy released per unit mass) in the phosphor approximates KERMA in tissue, and by design of dosimeter there will be a similar correspondence for absorbed dose. There are indications that the light conversion efficiency of lyoluminescent phosphors is not as dependent on LET as observed for thermoluminescent phosphors, and the possibility exists therefore, of an approximate tissue equivalent response in neutron and mixed radiation fields.

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