Monitoring anomalous fading of TL of feldspars by using far-red emission as a gauge

TL dating of feldspars of volcanic origin is thwarted by anomalous fading of its emission in the usual spectral range from UV to red, though in the far-red range it has been shown to be stable. A new method of evaluation of this anomalous fading is proposed. The comparison is no longer made directly between total TL emissions after different storage times. Instead, TL is first measured in two spectral ranges simultaneously, the ‘blue’ one, usually monitored for fading, and the far-red one. Secondly, at every temperature the ratio of ‘blue’ to far-red, named B_ir, is computed. Thirdly, to monitor anomalous fading, these ratios are compared between different TLs. When fading shows, values of B_ir are observed to decrease during storage, according to the logarithmic law, down to very low values. A temperature dependance of anomalous fading is firmly established.