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Doppler Coefficient Measurements on Th and ThO2 Rods with Nonuniform Temperature Distributions

W. G. Pettus, and M. N. Baldwin

Nuclear Science and Engineering

Volume 26 / Number 1 / September 1966 / Pages 34-46


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Measurements of the Doppler effect in resonant neutron capture have been made for samples having a nonuniform temperature distribution. These measurements were made on thorium and thorium-dioxide rods of approximately 3/4-in. diam. An activation technique was used, and the samples were exposed in a cadmium thimble at the center of a pool research reactor. The activated samples were dissolved, and the 233Pa was separated out and gamma counted. The Doppler coefficients for identical samples were determined with an axial heat source and with a peripheral heat source. In the axially heated cases, measurements were made with radial temperature drops ranging up to 185°C for the metal samples, and up to 1000°C for the oxide samples. In the peripherally heated cases, the temperature was uniform through the samples, and measurements were made with the temperature ranging up to about 350°C for both metal and oxide samples. The results show that the Doppler coefficient as a function of the average sample temperature is essentially the same for both axial and peripheral heating over the temperature range investigated. The measured values of the Doppler coefficients for the nonuniform temperature cases were (85 ± 5) × 10-4 and (95 ± 19) × lO-4 (°K) for thorium metal and oxide, respectively.

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