Bq is Bequerel, but I can't exactly recall its definition. I think it's either the number or energy of emissions per unit of time. My nuke books are all buried at the moment and CRC is unhelpful on the subject.

The data for massive radiation exposure came from Hiroshima and Nagasaki. It was not really possible to seperate radiation injury from blast and heat with any exactness. Lower level exposure data mostly comes from medical radiation treatment records. Those are generally distorted by the presence of cancer.

There is a big difference between external radiation exposure and the more dangerous incorporation of emitters in tissue. The latter is the case with Radon gas. Its alpha emission is stopped and absorbed by any amount of clothing or moisture or outer skin, but any that decays in the lungs injures the live cells and deposits radioactive heavy metals (Polonium isotopes) which do further damage while decaying to lead. Chemically toxic, too. Nasty stuff.

Obviously, controlled experiments can't be conducted in this realm.