Cosmogenic isotope anomalies

Cosmogenic isotope effects are generated by the interaction of matter with high-energy cosmic rays that are produced primarily by the Sun. Such reactions are induced not only by the cosmic rays, which consist largely of protons and a-particles (He nuclei), but also by the secondary particles, particularly neutrons, which are generated in primary reactions. In many cases, such 

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More important to MC-ICP-MS measurements are the minor cosmogenic isotope anomalies that can interfere with studies of nudeosynthetic, radiogenic and stable isotope effects. A prominent example are the cosmodiemical MC-ICP-MS W isotopic analyses that are carried out primarily to detect variations in the abundance of from the decay of now extinct Hf (Table 10.2). Such variations are most commonly detected by the measurement of or which are... 

Variations in isotopic abundances that are caused by nuclear reactions induced by cosmic rays are most commonly utilized in cosmic ray exposure dating, but this employs isotopes that are measured by either accelerator or noble gas mass spectrometry [28, 29]. In fact, there are only a very limited number of elements that are suitable for the study of cosmogenic isotopic variations, which can be readily analyzed by either TIMS or MC-ICP-MS [28]. The most important application of these techniques are studies of the secondary neutron fluxes that are generated by (primary) cosmic rays. Such measurements aim to detect anomalies in Sm, Gd, and Cd isotopic abundances that are produced by (n,y) reactions, for example " Cd(n, y) Cd. Many of these investigations were conducted by TIMS [137-139], but some cosmogenic Cd isotope variations of lunar rocks and soUs were evaluated based on MC-ICP-MS isotope ratio data that were originally acquired as part of a stable isotope study [134]. 

He) were able to show that some iron meteorites and lunar rocks also have cosmogenic W isotope anomalies that are superimposed on the radiogenic isotope effects. For the lunar rocks, these anomalies were shown to be due to the Ta(n,Y) a reaction, induced by cosmic radiation, whereby the short-lived isotope a (T = 114 days) subsequently decays to [141]. For the iron meteorites, cosmic ray-induced reactions lead to both the production and consumption of various W isotopes. As a result of these reactions, many samples of both magmatic and non-magmatic irons appear to have ratios that are... 

However, cosmogenic reactions can also produce small variations in the abundances of stable isotopes. Such anomalies can be difficult to resolve from radic enic, nudeosynthetic, and stable isotope effects and, if undiscovered, can lead to erroneous data interpretations. Targeted measurements of isotopes that are generated at particularly high levels by such cosmogenic reactions (e.g., Sm, have... 

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