July 1969 Brief 69-10249

is NASA TECH BRIEF

NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, to encourage their commercial application. Copies are available to the public at 15 cents each from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151.

Tungsten Thermal Dosimeter

Tungsten-184 has been found to be a useful dosim- concurrently for accurate determination of the radia- eter for thermal , particularly in high- tion exposure. temperature applications. The reliability of tungsten- Notes: 184 as a dosimeter has been verified against a stand- I. The naturally occurring , -tungsten-184, has ard dosimeter, -59, in a wide range of tempera- been shown to be an effective thermal neutron ture and nuclear environments. flux monitor for high-temperature (11 00' to 3300'K) Short-term irradiation (< 40 hours) of tungsten-clad, irradiations up to 200 hours. tungsten- dioxide fuel-plate test specimens at 2. The thermal neutron capture cross section of this high temperatures produced neutron dosimetry prob- isotope was measured to be 1.94 ± 0.08 barns (95% lems. The high temperature of the irradiation (1100° confidence level). to 3300'K) did not allow the use of standard dosime- 3. Documentation is available from: . ters, such as the of cobalt, , or Clearinghouse for Federal Scientific , to determine the thermal neutron flux because and Technical Information of their relatively low melting points (1768, 1336 0 , Springfield, Virginia 22151 and 1680°K, respectively, in contrast to the melting Price $3.00 point of tungsten, 3683'K). The use of fission products Reference: TSP69-10249 such as cesium-137 or -95 as a measure of 4. Technical questions may be directed to: burnup was not reliable, as specimens lost fission Technology Utilization Officer products during irradiation. The shorter term irradia- Lewis Research Center tions, in some cases four hours or less, did not produce 21000 Brookpark Road sufficient change in the ratio of uranium-236 to Cleveland, Ohio 44135 uranium-235 to accurately determine the uranium Reference: B69-10249 burnup. Patent status: The problem was resolved by using naturally oc- No patent action is contemplated by NASA. curring tungsten-184 in the specimen cladding as the Source: L. L. Ball, P. J. Richardson thermal neutron flux monitor. Tungsten-185 activity, and D. W. Sheibley which is produced by of tungsten- Lewis Research Center 184, was used to determine the thermal neutron flux. (as part of the Nuclear Rocket Program) Radiochemical separation methods and counting (LEW- 10880) techniques for irradiated tungsten were developed

Category 02

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