| Abstract: | SUMMARIES. This work summarizes the results of a several-year study of monitoring the post-radiation effect (PRE) for various kinds of pulp and paper depending on changes in relative humidity, on the type of the light source and dose of irradiation, and on secondary irradiation. Diffusion from the irradiated surface was also detected.
CONCLUSION. The results of the experiments monitoring the effect of the irradiation source and the subsequent storage conditions on the change of the brightness of various kinds of paper materials during storage (PRE) indicated that: • For comparable darkening caused by irradiation, PRE is more intense for ma¬terials irradiated by a source of daylight compared with a high-UVA source; • following irradiation by daylight, the dependence of PRE on the relative hu¬midity increases rapidly between values of 53% and 62%; • the dependence of PRE on the relative humidity during irradiation by high-UVA light was not monitored systematically; however, preliminary experi¬ments indicated that it will be less marked; • the initial phase of heat ageing copies the course of PRE (negative or positive PRE); here it would be possible to experimentally verify the correlation be¬tween natural and accelerated ageing under various conditions in relation to loss of brightness, reflectance spectra, etc.; • coloured compounds or the precursors of yellowing pass from the irradiated sheet into the neighbouring paper sheet that is in contact with the irradiated surface. |
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