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

Experiments were designed to study the effect of laboratory optical bleaching on thermoluminescence (TL) sensitivity change using fine grains 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 progressively increased laboratory doses. The sensitivity increase tends to become significant at a threshold dose and seems to approach an upper limit of 20-30% increase compared with the sensitivity of the unbleached young sample. The implications of the results for dating relatively old loess samples are discussed and ways of correcting and circumventing the sensitivity change are explored.