NUCLEAR-DEBRIS FORMATION 2 Table 2— AVAILABILITY OF GAMMA-PHOTON EMISSION DATA FOR FISSION PRODUCTS WITH HALF-LIVES LESS THAN 10 HR Half-life range Total number of nuclides in program Number for which gamma data are not available 0 tol min 311 296 66 q 1 to 5 min 5 to 10 min 10 to 30 min 30 to 60 min L to 10 hr 106 19 32 3 19 100 2 3 2% of the total activity. At times earlier than 10 min, the uncertaint: in the abundances, previously discussed, compounds with the absenc: of gamma-photon data to make predictions uncertain. A second consideration, insofar as gamma-radiation prediction: are concerned, involves the reliability of the gamma data that ar« available. It is not possible to discuss this point generally since the data vary widely in this respect. For some of the nuclides, the literature provides extensive and detailed reports of gamma-emissio) studies, whereas for others only fragmentary data are available. Xray photon abundances are particularly difficult to find in the literature, but fortunately these seem to have relatively minor effects o: prediction of such properties as dose rates and ionization rates. Gamma-energy Conversion Data To predict dose rates one must apply conversion factors to the photon-emission rates to convert them to roentgens per hour at some point in a well-defined geometric situation wit! respect to the emitter. For fallout predictions the situation usually chosen is a point 3 ft above a uniformly contaminated infinite plane The conversion factors are a function of photon energy as well as o: the geometry of the situation. , For the case of dose-rate calculation at a point 3 ft above an infinite plane, conversion factors were calculated according to the methoc of Gates and Eisenhauer’® by using their tabulated “build-up”factors. The resulting conversion factors are a smooth function of energy whict can be approximated for computer use by a simple polynomial. It should be remarked that Gates and Eisenhauer calculations do not ex- tend below 0.2-Mev photon energies. Conversion factors below this point are obtained by linear extrapolation through the origin. A recent report®’ indicates that this extrapolation may be considerably in error. In the region from 0.2 to 5.0 Mev, the Gates and Eisenhauer calculations are generally considered reliable although there is very little experimental data to verify them. Any geometry, other available conversion curve—applicable to different for example—can be substituted into the program rather