Cosmogenic exposure age dating

To understand this situation, it is useful to imagine one in the place of a rock particle under an eroding surface.As the particle approaches the surface, it sees an exponentially increasing cosmic ray intensity and cosmogenic nuclide production rate.The degree of ‘protection’ provided by the magnetic field is greater at low latitudes (where the magnetic field lines run parallel to the surface) than at the poles (where they are perpendicular to the surface).Thus, the cosmic ray intensity at the equator is significantly lower than at the poles, although the average energy (or ‘rigidity’) of the cosmic rays is higher The primary cosmic rays which do manage to pass through the magnetic field strongly interact with the atmosphere and form a secondary cosmic ray ‘shower’, which is mostly made of neutrons and muons.Although several efforts have been made to directly measure production rate scaling with latitude and elevation using artificial H targets, all currently used scaling models are based on neutron monitor surveys.The oldest and still most widely used scaling model is that of Lal (1991).

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Initially, the concentration of the nuclide increases almost linearly with time, but after a while, some of these nuclides are lost due to radioactive decay.The most common examples of such paired measurements are = 0.The most important example of studies which require samples that plot on the zero erosion line are exposure dating studies of glacial retreat.During the 20 years or so that cosmogenic nuclide geochronology has been around, it has truly revolutionised various aspects of geomorphology, such as the study of volcanoes, river incision, landslides, glaciers, sediments, and faults.Table 8.1 lists the most commonly used cosmogenic nuclides.

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