/3>, Ail at 'e ihL Classified UNCLASSIFIED BNL-1986 Subject Category: PHYSICS UNITED STATES ATOMIC ENERGY COMMISSION A MEASUREMENT OF NEUTRON TEMPERATURE IN A URANIUM ROD-WATER MODERATED LATTICE By H. Kouts K. Downes G. Price R. Sher 19E August 16, 1954 Brookhaven National Laboratory Upton, New York Technical Information Service, Oak Ridge, Tennessee Work performed under Contract No. AT (30-2) -Gen- 16. Date Declassified: October 27, 1955. This report was prepared as a scientific account of Govern- ment-sponsored work and is made available without review or examination by the Government. Neither the United States, nor the Commission, nor any person acting on behalf of the Commis- sion makes any warranty or representation, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any infor- mation, apparatus, method, or process disclosed in this report may not infringe privately owned rights. The Commission assumes no liability with respect to the use of, or for damages resulting with respect to the use of any information, apparatus, method, or proc- ess disclosed in this report. This report has been reproduced directly from the best available copy. Issuance of this document does not constitute authority for declassification of classified material of the same or similar content and title by the same authors. Printed in USA, Price 15 cents. Available from the Office of Technical Services, Department of Commerce, Wash- ington 25, D. C. GPO 987852 A MEASUREMENT OF NEUTRON TEMPERATURE IN A URANIUM ROD-WATER MODERATED LATTICE By H. Kouts, K. Dovnes, G. Price, and R. Sher Abstract : The relative danger coefficients of boron and cadmium have been measured in an assemnly of 1.15£ enriched uranium rods in ordinary water, at a water to uraniuB volume ratio of 3. The experiment consisted in finding the relative effects on neutron Multiplication of measured amounts of boron and cadmium in the water moderator. The ratio of the observed danger coefficients is a measure of the ratio of the cross-sections of the two poisons, and since the two have very different cross -section curves in the thermal range, a basis for the estimation of a neutron temnerature exists. The measurement resembles somewhat one done by G e P. Gavin (KAPL - 114.2). Under the assumption that the thermal neutrons have a Maxwell distribution of velocities, the measurement lmnlies a characteristic temperature of .0262 ± .00L4. volts (304° ± 16° °K). The water temperature at the time of the measure- ment was 297 °K. Experimental Methods ; A lattice of 1.15^ enriched uranium rods, .600" diameter, was loaded in a light water moderator until a multiplication of about 500 was reached. The method of loading, and the safety precautions were as described in BNL Log No. C-7605 (Safety of Subcritical Loadings in T-526) , except that now the console and instrumentation have been greatly improved. For instance, during the measurement described in this report the flux levels were monitored by six separate detectors and channels of instrumentation, and the safety rod - 2 - was set to trip on any one of four flux level monitors. In addition, a manual rod trip and a manual water dump were available. After this predetermined stopping point had been reached, the source was re- rroved, and the count rate from multiplication of spontaneous fission neutrons was measured. A measured amount of boric acid solution was added to the water moderator, after the equivalent volume of nure water was removed, and the count rate was again measured. A measured amount of cadmium sulphate solution was then added (again after removal of the same volume of moderator) , and the count rate was measured a third time. Three counters were used to measure the flux levels at each stage. One was a small BF, counter at the center of a triangular lattice cell; the second was a small enriched uranium fission chamber at the center of a triangular lattice cell, and the third was a fission ehanber located inside a fuel rod. Three de- tectors were used in order that independent checks on the results might be had; they also increased the statistical accuracy, in that the determination of relative flux level would be based on adding up the count rates from all counters. Vhile the flux level measurements were made, the water temperature was monitored by means of & chronel-alumel thermocouple. Analysis ; The reciprocal of the observed count rate is, for loadings sufficiently near critical, linear in k -_: eff ioc - *.„ - 1 - k _.*^ If a snail amount of poison is added to the moderator, as was done here, k _ will eff -3 - change because of the effect on f. For sufficiently snail increments, the change in k ~- is proportional to the macroscopic cross-section of the poison in the moderator : S» k eff *< 2 pbi»on and we suppose this relation to hold for the poison concentrations used in this measurement. We let the subscripts 0, 1, 2 refer respectively to situations where the moderator was pure water, where it contained boron, and where it con- tained boron and cadmium. Further, we let the changes in k -* produced by the addition of the boron and the cadmium be respectively -^and - A . 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