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Determination of Eta by Comparison of for U233 and Pu239 with for U235 in a Flux Trap Critical Assembly

R. Gwin, D. W. Magnuson

Nuclear Science and Engineering / Volume 12 / Number 3 / March 1962 / Pages 359-363

Technical Paper / dx.doi.org/10.13182/NSE62-A28086

The values of eta for U233 and eta for Pu239 have been determined by a reactivity coefficient measurement. An aqueous solution of each isotope was introduced axially into a critical cylindrical annular flux trap reactor, and the resulting reactivity change was measured by period determinations. From these data the ratios and were obtained. Using recently measured values of eta for U235 and the absorption cross sections in this ratio, the thermal values of 2.317 ± 0.040 for eta of U233 and 2.032 ± 0.053 for eta of Pu239 are obtained. Correction to a neutron velocity of 2200 meters/sec by using the appropriate g-factor gives a value of 2.317 ± 0.040 for eta of U233 and 2.082 ± 0.054 for eta of Pu239.