The atmospheric loss issue is as bad as the bogeyman of no magnetic field. Earth's atmosphere stops most cosmic rays which barrel right through our magnetic field. It's simply a matter of mass interference. 14.67 PSIG of atmosphere or something like 3 feet of rock provides enough mass that there is little chance of energetic particles making it through. Mars' atmosphere will eventually bleed away, but it is a matter of at least a million years according to Chris McKay If I recall his answer to my question along those lines correctly. It was certainly far longer than the time required to produce it. My terraforming book lists J.E. Oberg as an authority on this issue as author of the book "New Earths" and several other articles.

Regards,
Mark