Studying the constancy of galactic cosmic rays using cosmogenic radionuclides and noble gases in iron meteorites

During their orbit in space, extraterrestrial bodies are exposed to cosmic rays. The interaction between these energetic particles and the meteoroides produce both stable and radioactive cosmogenic nuclides that can be used to study, e.g., the size of the meteorite before ablation in the Earth’s atmosphere and the time the object traveled before falling on Earth (exposure age). For a proper interpretation of such data, especially the ages, the temporal constancy of the cosmic ray intensity has to be proven. Doing so and being interested in timescales in the range of a few hundred million years, we have to rely on iron meteorites because their exposure ages range from a few million to a few billion years.
In this study, we systematically investigate the exposure ages of iron meteorites and search for periodic structures in the age distribution. So far, we have studied 28 iron meteorites for ¹⁰Be, ²⁶Al, and ³⁶Cl at the DREsden Accelerator Mass Spectrometry (DREAMS) facility [1] and for the noble gas isotopes of He, Ne, and Ar at the University of Bern. The first ⁵³Mn and ⁶⁰Fe measurements have already been performed at the Australian National University (ANU) and at the TUM (Munich). Finally, ⁴¹Ca measurements at DREAMS to identify long terrestrial residence times influencing the radionuclide concentrations are foreseen for the very near future.
The measurements of additional iron meteorites, which will help improving the statistics of the age distribution as well as extending the list of radionuclides and also extending the study to mineral separates from iron meteorites, are currently ongoing.
[1] Akhmadaliev, S. et al. (2013) NIMB 294, 5.