used. FRC states that the operational mechanism described for application of criteria to limit the whole body dose for individuals to 0.5 rem per year and to limit exposure of a suitable sample of the population to 0.17 rem per year is likely to assure that the gonadal exposure guide will not be exceeded. The child, infant, and unborn infant are identified as being more sensitive to radiation than the adult. Exposures to be compared with the guidance are to be derived for the most sensitive members in the population. The guide for the individual applies when in- dividual exposures are known; otherwise, the guide for a suitable sample (one-third the guide for the individual) is to be used. This operational technique may be modified to meet special Situations. The FRC primary numerical guides, expressed in rem, are provided in two reports, FRC Nos. 1 and 2, summarized in Table I. Secondary numerical guides developed by FRC are expressed in terms of daily intake of specific radionuclides corresponding to the annual RPG's. Consideration is given to all radionuclides through all pathways to derive a total annual exposure for comparison with FRC guides. However, for many practical situations, relatively few radionuclides yield the major contribution to total exposure; by comparison, exposures from others are very small. TABLE I . FRC RADIATION PROTECTION GUIDES VV INDIVIDUAL POPULATION GROUP Whole body Gonads 0.5 rem/yr - 0.17 rem/yr 5 rems/30 yrs Bone marrow Bone 0.5 rem/yr 1.5 rems/yr 0.17 rem/yr 0.5 rem/yr Thyroid 2/ 1.5 rems/yr 3/ Bone (alternate — guide) 0.003 pg of 0.5 rem/yr 2262, sn adult 9.001 pg of skeleton 226 Ra in adult skeleton 1/ For conditions and qualifications see FRC Report Nos. 1 and 2. 2/ Based upon a child's thyroid, 2 gms in weight and other factors listed in paragraphs 2.10-2.14 of FRC Report No. 2. 226, 3/ Or the biological equivalents of these amounts of VI-2 ae