"First, we mast consider what part of the natural radiation, if any, is similar to the radiation of strontium-90 in biological effect so we can say without doubt and hesitancy that the physiological effects, whatever they are, will be the same for the same energy absorbed. cosmic rays seem to fit this bill. | Fortunately, the In other words, we are at liberty to compare the cosmic ray radiation dosages with the dosages from radiostrontium in our bone structure. fhe reason this is permissible is that the ionization density along the tracks of the mi=mesons which are the principal coamic ray components at sea level and at altitudes of 5,000 feet are nearly the | same as those of the yttrium-90 beta rays, the principal radiation which radiostrontium emits; that is, radiostrontium has a radioactive daughter, yttrium-90, which emits a very energetic beta ray and the ionization density alongthe track of this radiation is very similer to that of the m-mesons of the cosmic rays and their disintegration electrons, and it is generally accepted by health physicists and radiobiologists that radiations of the same ionization density have very similar, if not identical biological effects for the same energy absorbede The high energy of the yttrium~-90 gives it an average distance of penetration in tissue of 2 millimeters so any effect of local non-uniformity of deposition of strontium-90 in the bone is removed. The cosmic ray exposure is, of course, uniform throughout the bone structure. Therefore, we can equate cosmic ray dosage with strontium-90 dosage and thus it is possible for us to say that the difference between one altitude and another is equal in effect, other effects being equal, to a certain number of Sunshine Units in bone." |