SENSITIVITY CHANGE OF THERMOLUMINESCENCE SIGNALS AFTER LABORATORY OPTICAL BLEACHING - EXPERIMENTS WITH LOESS FINE GRAINS

Experiments were designed to study the effect of laboratory optical bl eaching on thermoluminescence (TL) sensitivity change using fine grain s extracted from Chinese loess. There is a tendency for an increase in TL sensitivity after laboratory bleaching treatment for 'artificially aged' samples, i.e. subsamples of a young sample irradiated with prog ressively increased laboratory doses. The sensitivity increase tends t o become significant at a threshold dose and seems to approach an uppe r limit of 20-30% increase compared with the sensitivity of the unblea ched young sample. The implications of the results for dating relative ly old loess samples are discussed and ways of correcting and circumve nting the sensitivity change are explored.