Radon Escape from Bone Mineral

It has been known for a long time that when Ra226 is deposited in bone the first daughter, radon, born in the a-decay of radium, escapes readily from the animal. In the human being who has carried radium for many years, about 70% of the radon atoms formed are found to escape (1); in a dog this value ranges from 90 % in the case of a short-term burden to 70% after several years (1, 2). Since the half-life of radon is 3.84 days, there is apparently sufficient time available before it decays to escape from the body via the lungs after it reaches the blood stream. Norris (personal communication, 1953) has postulated that radon is freed from its parent crystal by its recoil after the a-decay of radium. To investigate this hypothesis, we have attempted to produce changes in vitro in the structure of bone which would alter the escape of radon, and to see whether or not the recoil hypothesis is consistent with these results. As a consequence of these measurements the problem of dosimetry of radiumburdened bone by a-track autoradiography has been clarified considerably, since the retention of the a-emitting daughters of radon, both in living bone and in sections prepared for autoradiography, must be known to evaluate properly the significance of the number of a-tracks recorded in the emulsion. These measurements have been made and are described below.