1. The paper you link to does not discus ingestion. Ever. It clearly described to the dosimetric estimates of gamma and neutron, but no information on metabolic pathways.
I hate to tell you sir, but you in fact do test this every day you breathe, drink and eat. There ARE in fact many natural sources of radioactivity, that we have been eating for quite some time, with never a though of cancer.
Radioactive isotopes are one source of radiation, insolation and cosmic background radiation are others. In this case the OP was referring specifically to maximum radiation exposure levels as defined by some big-"I" international organization.
No. It is not. There is alpha, gamma, beta+ and beta-. And there is a huge difference. And how healthy it is strongly depends on the area of you body that is exposed. If Your skin is exposed to alpha radiation it can be as harmless as a sunburn (it's a matter of the dosis). If you get alpha radiator into your bloodstream that's a whole different story at the same dosis.
That still confuses radiation with radio-isotopes which are sources of radiation. If you consumed a highly radioactive isotope you would likely get more radiation not different radiation.
If a single bioloogically consumed radio-isotope molecule put out the same amount of radiation as the annular insolation in Denver, then you would likely get more localized damage from the ionizing radiation at its point of binding. If it were multiple molecules (measured in parts per billion) and they in aggregate summed to the annual insolation in Denver, then its no more dangerous than the annual insolation in Denver.
Alpha particles and energetically ejected electrons and positrons are ionizing radiation just like gamma rays, and its the amount and concentration, not the source, that matters.
I'm sorry. I didn't mean to imply daily. As professor Bernard Cohen meant it, as a competition with Ralph Nader, I was a one off meant to show that the equivalent mg dosage of caffeine would kill you much faster then plutonium. A daily ingestion is much different.
BTW, there's a big difference between "background radiation" and ingested radiation (either through air, food, water, etc.)
The scientific consensus is that there is no amount of radiation that is safe to ingest.
http://www.rrjournal.org/doi/pdf/10.1667/RR2629.1
Do you really want to test your theory?