@Ragman,
I think you got this phrase from the article in yesterday's WSJ. The article was confusing and its author was as well in my view. A new collection of units for measuring radiation effects has indeed arisen over the past two decades, however, it doesn't represent any new knowledge or understanding over the old system. Both xyxtems, new and old attempt to deal with four very distinct forms of what we call radiation (photons or gamma, electrons or beta, neutrons, and helium nucleii or alpha), each with different penetrating ability, ranges of energy levels, ranges of influence and biological effects per event.
In general alpha particles and, to a large extent, betas don't represent a real hazard as long as their source is outside the body. This is because of their very limited penetrating power - they hardly get through our clothing or skin. However, if the source is ingested and deposited within the body they can be a real hazard (Thus the alpha radiation from the thorium in your smoke detector is no hazard, as long as you don't eat it). Neutrons have greater penetrating ability, but they don't last long and have a mean free path of only about eight inches from their source. Gamma rays or photons come in a very wide range of energy levels, ranging from those associated with radio or phone transsmissions to others millions of times more energetic associated with some forms of solar radiation and the decay of radioactive nuclides. All have a very great penetrating power - we live our lives bathed in a steady stream of gamma radiation that reaches us from the sun, penetrating the entire atmosphere of the earth along the way.
Al, forms of radiation follow an inverse square reduction in their intensity as one moves away from the source. (Double the distance from the source and the intensity is reduced by a factor of four).
Interestingly living in a city at high altitude (say Denver or Aspen Colorado) involves an increased exposure to solar gamma radiation comparable to the maximum legal exposure for a radiation worker. Moving to Aspen is far worse in that the exposure there to radon gas eminating from the granite in the surrounding soil involves a significantly increased dose in a particularly hazardous form (and in total probably greater than the doses received by the unfortunate citizens of Fukushima). Public health data from cities at high elevations don't reveal any measurable effect on disease or mortality (except that teatotalling Mormons in Utah are generally healthier than cigar smoking boozers from Las Vegas).
