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[1009.3932] Time of primordial Be-7 conversion into Li-7, e

Posted: September 23 2010
by Neal Dalal
This is a neat result! This paper is about the final stage of Big Bang Nucleosynthesis (BBN). We normally think of BBN as occurring at extremely high redshift, e.g. [tex]z\approx 10^8[/tex]. Here they discuss a BBN process that occurs much later, at redshifts closer to [tex]10^4[/tex] or [tex]10^5[/tex].

Most of the [tex]^7[/tex]Li produced during BBN arises from the decay of [tex]^7[/tex]Be, through electron capture. The authors point out that this decay of [tex]^7[/tex]Be occurs much later than naively expected, because the electron capture rate is too low when Be atoms are fully ionized. Only at 100 eV temperatures are there sufficient numbers of bound electrons that [tex]^7[/tex]Be can decay to [tex]^7[/tex]Li.

It's unclear if this effect has any observable consequences, just because the number of [tex]^7[/tex]Be nuclei is so low. Still, at least for non-experts like me, it's surprising that nucleosynthetic processes can operate at such low temperatures.