Because of the roughly linear correlation between Be/H and Fe/H in low metallicity halo stars , it has been argued that a “ primary ” component in the nucleosynthesis of Be must be present in addition to the “ secondary ” component from standard Galactic cosmic ray nucleosynthesis .
In this paper we critically re-evaluate the evidence for the primary versus secondary character of Li , Be , and B evolution , analyzing both in the observations and in Galactic chemical evolution models .
While it appears that [ Be/H ] versus [ Fe/H ] has a logarithmic slope near 1 , it is rather the Be-O trend that directly arises from the physics of spallation production .
Using new abundances for oxygen in halo stars based on UV OH lines , we find that in Pop II stars for which O has been measured , the Be-O slope has a large uncertainty due to systematic effects .
Namely , the Be-O logarithmic slope lies in the range 1.3 - 1.8 , rendering it difficult to distinguish from the data between the secondary slope of 2 and the primary slope of 1 .
The possible difference between the Be-Fe and Be-O slopes is a consequence of the variation in O/Fe versus Fe : recent data suggests that the best-fit O/Fe-Fe slope for Pop II is in the range -0.5 to -0.2 , rather than zero ( i.e. , Fe \propto O ) as is often assumed .
In addition to this phenomenological analysis of Be and B evolution , we have also examined the predicted LiBeB , O , and Fe trends in Galactic chemical evolution models which include outflow .
Based on our results , it is possible that a good fit to the LiBeB evolution requires only traditional the Galactic cosmic ray spallation , and the ( primary ) neutrino-process contribution to ^ { 11 } B .
We thus suggest that these two processes might be sufficient to explain ^ { 6 } Li , Be , and B evolution in the Galaxy , without the need for an additional primary source of Be and B .
However , the uncertainties in the data at this time prevent one from reaching a definitive conclusion .
Fortunately , several observational tests of this “ neoclassical ” scenario are available ; we note in particular the importance of further observations to secure the O/Fe Pop II trend , as well as accurate measurements of B/Be , ^ { 6 } Li/Be , and ^ { 11 } B/ ^ { 10 } B in halo stars .