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12. II. Copy Reproduction and Distribution

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Neutron transmission measurements from 0.2 to 20.0 McV have been made for the shielding materials carbon, oxygen, aluminum, silicon, calcium, iron and the com pound silicon dioxide. The measurements were performed at the ORELA Shield Test Station with a resolution of about 0.12 nsec/meter on sample thicknesses varying from 0.65 to 0.9 atoms/barn. The transmission measurements were compared with the predictions obtained from the Defense Nuclear Agency evaluated cross-section library. Since the total cross-section files for these elements are also the ones present in the ENDF/B-I1I library, we are also checking its total cross-section files for all of the elements with the exception of oxygen. There are serious discrepancies between our data and the predictions based on the evaluated files. These discrepancies are ofcen large in the energy region from 0.2 to 0.6 MeV.