Remodeling of the Heavy-Water Facility of the Kyoto University Reactor for Epithermal and Thermal Neutrons

THE DIFFUSION LENGTH OF THERMAL NEUTRONS IN HEAVY WATER CONTAINING LITHIUM CARBONATE

Canadian Journal of Research ◽

10.1139/cjr47a-003 ◽

1947 ◽

Vol 25a (1) ◽

pp. 26-41 ◽

Cited By ~ 4

Author(s):

H. G. Hereward ◽

H. R. Paneth ◽

G. C. Laurence ◽

B. W. Sargent ◽

A. M. Munn

Keyword(s):

Cross Section ◽

Heavy Water ◽

Boron Trifluoride ◽

Capture Cross Section ◽

Diffusion Length ◽

Lithium Carbonate ◽

Mean Free Path ◽

Thermal Neutrons ◽

Capture Cross ◽

Cylindrical Tank

The density distribution of thermal neutrons was measured with a small boron trifluoride chamber in a cylindrical tank containing 113 litres of heavy water in which lithium carbonate was dissolved. The diffusion length was found to be 22.7 cm. in this solution containing 7.70 × 10−4 atoms of lithium per molecule of heavy water (99.4 atom % D). After corrections were applied for the capture of neutrons in the heavy water and light hydrogen, the capture cross-section of lithium was found to be 59 × 10−24 cm.2 per atom for neutrons of standard velocity 2200 m. per sec. from the measured diffusion length and known transport mean free path.

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ATTEMPT TO DETECT AN (n,2n) REACTION IN DEUTERIUM

Canadian Journal of Research ◽

10.1139/cjr48a-033 ◽

1948 ◽

Vol 26a (6) ◽

pp. 386-403 ◽

Cited By ~ 4

Author(s):

L. G. Elliott ◽

E. P. Hincks ◽

A. N. May

Keyword(s):

Density Distribution ◽

Heavy Water ◽

Boron Trifluoride ◽

Infinite Medium ◽

Fast Neutrons ◽

Neutron Density ◽

Thermal Neutrons ◽

Paraffin Oil ◽

Neutron Density Distribution ◽

Good Agreement

A detailed account is given of experiments carried out to detect an (n,2n) reaction in deuterium. A Po-α-Be neutron source was surrounded by a hollow aluminum sphere 30 cm. in diameter, which could be filled with heavy water. The sphere was surrounded by an effectively infinite medium of paraffin oil. The neutron density distribution outside the sphere was measured with a small boron trifluoride chamber (6 mm. diameter × 20 mm. long). The total integrated densities of neutrons were determined both with the sphere empty and filled with heavy water. After correcting for absorption of thermal neutrons by the heavy water, the aluminum sphere, and the source, and of fast neutrons by the oxygen of the heavy water, it is shown that the fraction of neutrons giving an (n,2n) effect is 0.1 ± 2.7%. This indicates that the effect is less than both that predicted by Höcker's theory (~ 10%) and that reported from an earlier experiment by Halban and coworkers (18%). However it is in good agreement with measurements made by Fenning and Knowles (1.4 ± 5%).

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THE TRANSPORT MEAN FREE PATH OF THERMAL NEUTRONS IN HEAVY WATER

Canadian Journal of Research ◽

10.1139/cjr47a-016 ◽

1947 ◽

Vol 25a (3) ◽

pp. 143-156 ◽

Cited By ~ 14

Author(s):

P. Auger ◽

A. M. Munn ◽

B. Pontecorvo

Keyword(s):

Linear Function ◽

Free Path ◽

Heavy Water ◽

Transport Theory ◽

Mean Free Path ◽

Neutron Density ◽

Thermal Neutrons ◽

Straight Line

The transport mean free path of thermal neutrons in heavy water is determined from measurements of the neutron density in heavy water (99.4 atoms of deuterium per 100 atoms of hydrogen element) at various distances from a cadmium plate. In the region investigated, the density is found to be a linear function of the distance from the cadmium plate. When this straight line is extrapolated, the density vanishes at a distance d = 1.64 cm. behind the plate. On the basis of transport theory it is known that d = 0.71 lt, where lt is the transport mean free path in the medium. The final result is lt = 2.4 cm. in pure heavy water. The measurements of the neutron density show that it falls below the straight line as the cadmium surface is very closely approached, in agreement with transport theory.

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THE DIFFUSION LENGTH OF THERMAL NEUTRONS IN HEAVY WATER

Canadian Journal of Research ◽

10.1139/cjr47a-015 ◽

1947 ◽

Vol 25a (3) ◽

pp. 134-142 ◽

Cited By ~ 12

Author(s):

B. W. Sargent ◽

D. V. Booker ◽

P. E. Cavanagh ◽

H. G. Hereward ◽

N. J. Niemi

Keyword(s):

Cross Section ◽

Heavy Water ◽

Capture Cross Section ◽

Diffusion Length ◽

Mean Free Path ◽

Effective Radius ◽

Neutron Density ◽

Thermal Neutrons ◽

Cylindrical Tank ◽

Relaxation Length

A continuous flux of thermal neutrons was passed into a large cylindrical tank of heavy water that sat on a graphite column containing a source of photoneutrons. The neutron density in the tank was explored with small indium detectors at selected points along two diameters at right angles in each of three horizontal planes and at 10-cm. intervals along the axis of the tank. The transverse measurements were fitted to Fourier–Bessel series in which the amplitudes of the harmonics were relatively small. The effective radius derived from the transverse analysis was the same in the three planes. The relaxation length of the first component was found from the axial measurements. Corrections were applied for the absorption of neutrons in the axial detector tube, enclosed framework, and indium detectors, and in the light hydrogen in the heavy water. The final value of the diffusion length of thermal neutrons in heavy water (100% D2O) is 171 ± 20 cm. Combining this with the known transport mean free path, the capture cross-section is (0.92 ± 0.22) × 10−27 cm.2 per molecule D2O for neutrons of velocity 2200 m. per second.

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