Radiation dosage in flight through the Van Allen belt.

A B O U T ten years ago, when avialion medicine developed a seri,ous interest in the problem of cosmic ray ,hazards in flight at the top of and outside the atmosphere, it became common practice to express cosmic ray intensities in terms of tissue ionization dosages, that is, in roentgens equivalent physical ( rep) . This expedited ~he interpretation of the ~;lata of the physicists inasmuch as exposures quoted in rep or milli-rep immediately convey, to the radiobiologist, an idea about the effects on living matter to be expected. On the other hand, one should realize that dosages derived in this manner are not representative of the true exposure that would prevail if a ~human ,body were to replace the measuring device. Though cosmic ray intensities are often given in units of ion pairs per c.c. of standard air, thereby lending themselves easily to the indicated conversion, they usually have been measured with equipment which does not fulfill the requirements