Cosmogenic exposure dating
The basic principle is that these radionuclides are produced at a known rate, and also decay at a known rate.
Accordingly, by measuring the concentration of these cosmogenic nuclides in a rock sample, and accounting for the flux of the cosmic rays and the half-life of the nuclide, it is possible to estimate how long the sample has been exposed to cosmic rays.
These elements have always been present in the Earth's crust and atmosphere, and are concentrated in some places, such as uranium orebodies which may be mined.
The term NORM exists also to distinguish ‘natural radioactive material’ from anthropogenic sources of radioactive material, such as those produced by nuclear power and used in nuclear medicine, where incidentally the radioactive properties of a material maybe what make it useful.
Results from other sliding surfaces are different and suggest accelerated displacement rates today.
Terrestrial cosmogenic nuclide surface exposure dating of moraine boulders and alluvial fan sediments define the timing of five glacial advances over at least the last five glacial cycles in the Ladakh Range of the Transhimalaya.
Material giving rise to these enhanced exposures has become known as naturally occurring radioactive material (NORM).Surface exposure dating provides critical information on a range of Earth science problems including ages of glacial features, erosion rates, and rates of fault motion.The technique relies on the production of rare isotopes produced by interactions of cosmic rays with target nuclei in rocks within ~ 1 meter of Earth's surface.We observe a pattern of progressively more restricted glaciation during the last five glacial cycles, likely indicating a progressive reduction in the moisture supply necessary to sustain glaciation.A possible explanation is that uplift of Himalayan ranges to the south and/or of the Karakoram Mountains to the west of the region may have effectively blocked moisture supply by the south Asian summer monsoon and mid-latitude westerlies, respectively.