Galactic cosmic rays

Be is a very interesting element, produced by spallation of galactic cosmic rays. The only two usable lines are in the extreme UV (313 nm), in a crowded spectral region, and the stellar radiation is heavily absorbed by the earth s atmosphere, so that their observations are challenging in faint stars. Only very recently (Pasquini et al. 2004) the first Be observations became available, in 2 TO stars of the nearby NGC6397. 

Fig. 9.9. Galactic chemical evolution of 6Li, according to models with and without cosmological cosmic rays, the former providing a plateau at low metallicities. After Rollinde, Vangioni-Flam Olive (2005).

In this textbook many exciting topics in astrophysics and cosmology are covered, from abundance measurements in astronomical sources, to light element production by cosmic rays and the effects of galactic processes on the evolution of the elements. Simple derivations for key results are provided, together with problems and helpful solution hints, enabling the student to develop an understanding of results from numerical models and real observations. 

Reeves H, Fowler WA, Hoyle F (1970) Galactic cosmic ray origin of Li, Be and B in stars. Nature 226 727-729... 

The study of galactic cosmic rays is perhaps more an exercise in taste than in visual appreciation. In fact we determine their composition without ever really seeing them. However, they constitute the only sample of matter in our possession that comes from outside the Solar System. The chemical and isotopic composition of this sample is measured using balloon- or satellite-borne particle detectors, since the Earth s atmosphere is fatal to them. When they slam into nuclei in the air, they fragment into tiny particles, thereby losing their original identity. 

Li, Be, and B are believed to be produced in spallation reactions in which the interstellar 12C and 160 interact with protons in the galactic cosmic rays (GCR). These reactions are high-energy reactions with thresholds of 10-20 MeV. The energy spectrum of the GCR is shown in Figure 12.20. 

Shamir and Veizer (2003) found, for instance, a high correlation between the intensity of galactic cosmic rays and temperature for the last 500 million years. On this basis, it was concluded that 75% of temperature variability in that period had been determined by the contribution of this factor (this problem was also considered earlier by Kondratyev, 1998b). 

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