irradiation of thiobacillus

[GEO]

Hello All,

I'm trying to find the total dossage required to sterilize a sample of
gold tailings using a cobalt-60 source.  As long as the thiobacillus
ferro-oxidans is irradiated, that should be sufficient.  A short
literature review mentionned both 2 Mrad (1969) and 5 Mrads (1994??).
I'm hoping someone out there has more recent data.

Thanks, 
Rod