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Reasons for a temporal decrease (fading) in the accumulated energy in feldspars used as paleodosimeters are considered. The tunneling processes capable of leading to fading as well as temperature and time dependences of tunnel afterglow have been studied in detail. It is shown that this glow bears no direct relation to the possible tunnel depletion of the dosimetric trapping centers. With a view toward directly observing tunneling from these centers, the temperature dependences (from −200 o C to +100 o C) of the intensity of the luminescence stimulated in the IR band with λ + 900 nm (of the optically stimulated luminescence (OSL) signal) have been studied in detail. Within the limits of sensitivity of the equipment used, tunneling from the dosimetric centers has not been detected. It has been inferred that in fading of the OSL signal, an essential role can be played by the traps that are depleted at 200 o C and have a lifetime of about 2 years at room temperature.Introduction. tunneling processes can play an important role in relaxation of the energy of ionizing radiation stored in feldspars of various modifications. These processes are connected with the phenomenon of the so-called anomalous fading, which consists of more rapid escape of charge carriers trapped at deep capture levels than is expected during their purely thermal release. The great interest in the phenomenon of anomalous fading is due to the fact that it serves as a source of errors in luminescent dating of geological deposits on the basis of extractions of feldspars. In natural irradiation of minerals, a quasi-equilibrium state is established at a lower level of stored energy than in laboratory irradiation to comparable doses, because tunneling relaxation, especially its late stages, are much longer processes than the procedure of laboratory irradiation. This leads to revaluation of the dose sensitivity of the specimens being dated and thereby to their seeming "rejuvenation." An allowed moderate period of expectancy after laboratory irradiation also does not solve the problem, because not knowing the intensity of the tunneling processes, the expectancy time remains uncertain, not to mention that the needed period may last for many years.Although the tunneling processes in feldspars have been studied in a number of works (see, for example, [1, 2]), to solve the problem of their relation to the phenomenon of anomalous fading, the data available are clearly in short supply. The earlier studies were mainly concerned with tunneling afterglow in various modifications of feldspars, but the problem of tunneling processes occurring directly from deep dosimetric capture levels has remained unsolved. Refinements are also necessary for the analysis of the kinetics of the tunneling processes as well as the relation of the tunneling parameters to the degree of ordering of the crystal lattice of different modifications of feldspars (in the sense of the presnece or absence of order in the mutual disposition of the AlO 4 -and SiO 4 tetrahedrons in the skeleton of...

Abstract:An increasing amount of evidence shows that the use of feldspars in luminescence dating may suffer from significant age underestimates, which are thought to result from anomalous fading. In the hope of finding a solution to the problem we undertook physical investigations of kinetics and temperature dependencies of tunnel afterglow of these minerals. As a result, the method of the direct detection of the tunnel transitions from the dosimetric traps is proposed. Some other relevant results obtained are also presented and discussed. Particularly, the probable reasons of absence of effects of anomalous fading in the feldspar samples investigated in the present work are elucidated.