MEASUREMENT OF THE DIFFUSION LENGTH OF THERMAL NEUTRONS IN GRAPHITE

1947 ◽  
Vol 25a (1) ◽  
pp. 15-25 ◽  
Author(s):  
H. G. Hereward ◽  
H. R. Paneth ◽  
G. C. Laurence ◽  
B. W. Sargent
Keyword(s):  
Density Distribution ◽  
Diffusion Length ◽  
Probable Error ◽  
Rectangular Parallelepiped ◽  
Thermal Neutrons ◽  
Dysprosium Oxide

The theory and method of measuring the diffusion length of thermal neutrons in graphite are discussed in detail. The graphite pile was a rectangular parallelepiped, 185.8 cm. square and 153.6 cm. high. The source was 1.2 gm. of radium mixed with beryllium. Part of the pile was used to slow down the neutrons to thermal velocities, and the density distribution of thermal neutrons was explored in the remainder of the pile with detectors of dysprosium oxide. The diffusion length of thermal neutrons in this graphite of average pile density 1.55 gm. per cc. was found to be 51 cm., with a probable error of 3 cm.

The diffusion length of thermal neutrons in water between 18 and 255 °C

1966 ◽  
Vol 289 (1418) ◽  
pp. 342-352 ◽  
Keyword(s):  
Cross Section ◽  
Close Agreement ◽  
Diffusion Length ◽  
Slow Neutron ◽  
Thermal Neutrons ◽  
Absorption Cross ◽  
A Value ◽  
Length Measurements ◽  
Theoretical Predictions ◽  
Made In

The diffusion length of thermal neutrons in water has been measured at various temperatures between 18 and 255 °C, the source being 124 Sb-Be (25 keV). Diffusion length measurements were also made in water with three boric acid concentrations and with water poisoned with a cadmium sulphate solution, the measurements being taken over a temperature range of 18 to 200 °C. The variation with temperature of the diffusion coefficient of water was determined from the experiments with poisoned water. A value 0.324 + 0.006 barn was obtained for the 2200 m/s microscopic absorption cross section of hydrogen. Close agreement was found between the experimental results and theoretical predictions based on the Nelkin model for slow neutron scattering.

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

1947 ◽  
Vol 25a (1) ◽  
pp. 26-41 ◽  
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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