Tungsten-185 activity, which is produced by neutron activation of tungsten-184, determines thermal neutron flux. Radiochemical separation methods and counting techniques for irradiated tungsten provide accurate determination of the radiation exposure

Ball, L. L.

Richardson, P. J.

Sheibley, D. W.

English

NASA Technical Reports Server

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 Neutron Dosimeter 
.
Tungsten-184 has been found to be a useful dosim-
eter for thermal neutrons, particularly in high-
temperature applications. The reliability of tungsten-
184 as a dosimeter has been verified against a stand-
ard dosimeter, cobalt-59, in a wide range of tempera-
ture and nuclear environments. 
Short-term irradiation (< 40 hours) of tungsten-clad, 
tungsten-uranium dioxide fuel-plate test specimens at 
high temperatures produced neutron dosimetry prob-
lems. The high temperature of the irradiation (1100° 
to 3300'K) did not allow the use of standard dosime-
ters, such as the isotopes of cobalt, dysprosium, or 
gold, to determine the thermal neutron flux because 
of their relatively low melting points (1768, 1336 0 , 
and 1680°K, respectively, in contrast to the melting 
point of tungsten, 3683'K). The use of fission products 
such as cesium-137 or zirconium-95 as a measure of 
burnup was not reliable, as specimens lost fission 
products during irradiation. The shorter term irradia-
tions, in some cases four hours or less, did not produce 
sufficient change in the ratio of uranium-236 to 
uranium-235 to accurately determine the uranium 
burnup. 
The problem was resolved by using naturally oc-
curring tungsten-184 in the specimen cladding as the 
thermal neutron flux monitor. Tungsten-185 activity, 
which is produced by neutron activation of tungsten-
184, was used to determine the thermal neutron flux. 
Radiochemical separation methods and counting 
techniques for irradiated tungsten were developed
concurrently for accurate determination of the radia-
tion exposure. 
Notes: 
I. The naturally occurring isotope, -tungsten-184, has 
been shown to be an effective thermal neutron 
flux monitor for high-temperature (11 00' to 3300'K) 
irradiations up to 200 hours. 
2. The thermal neutron capture cross section of this 
isotope was measured to be 1.94 ± 0.08 barns (95% 
confidence level). 
3. Documentation is available from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Price $3.00 
Reference: TSP69-10249 
4. Technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B69-10249 
Patent status: 
No patent action is contemplated by NASA. 
Source: L. L. Ball, P. J. Richardson 
and D. W. Sheibley 
Lewis Research Center 
(as part of the Nuclear Rocket Program) 
(LEW- 10880) 
Category 02 
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Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
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Tungsten thermal neutron dosimeter

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