THE DIFFUSION LENGTH OF THERMAL NEUTRONS IN HEAVY WATER

1947 ◽  
Vol 25a (3) ◽  
pp. 134-142 ◽  
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.

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.

THE TRANSPORT MEAN FREE PATH OF THERMAL NEUTRONS IN HEAVY WATER

1947 ◽  
Vol 25a (3) ◽  
pp. 143-156 ◽  
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.

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 CAPTURE CROSS-SECTION FOR THERMAL NEUTRONS OF CADMIUM, LITHIUM6, BORON10, BARIUM, MERCURY AND HYDROGEN

1941 ◽  
Vol 19a (3) ◽  
pp. 33-41 ◽  
Author(s):  
E. L. Harrington ◽  
J. L. Stewart
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Capture Cross Section ◽  
Comparison Method ◽  
Thermal Neutrons ◽  
Capture Cross ◽  
Scattering Effect ◽  
Capture Cross Sections

A comparison method of measuring, by using solutions, the capture cross-sections for thermal neutrons is described. The chief advantages are directness, simplicity, and freedom from uncertainties as to direction of path, or as to the magnitude of the scattering effect. The method is best suited to nuclei of large cross-sections. Assuming the well checked value for the cadmium nucleus to be correct, the capture cross-sections of certain other nuclei were determined. The results for barium and for hydrogen differ widely from values previously published.

EVIDENCE FOR AN (n, α) REACTION INDUCED IN O17 BY THERMAL NEUTRONS

1947 ◽  
Vol 25a (2) ◽  
pp. 77-87 ◽  
Author(s):  
A. N. May ◽  
E. P. Hincks
Keyword(s):  
Cross Section ◽  
Neutron Capture ◽  
Ionization Chamber ◽  
Capture Cross Section ◽  
Thermal Neutrons ◽  
Thermal Neutron Capture ◽  
Energy Bands ◽  
A Value ◽  
Neutron Reactions ◽  
The Masses

It can be shown from the masses involved that the reaction O17 (n, α) C14 should be exothermic by 1.72 Mev., and should therefore occur with thermal neutrons. As an attempt to detect the reaction an investigation was made of the pulse spectrum produced when an ionization chamber containing oxygen was placed in a flux of thermal neutrons. The pulses were amplified and then counted in a series of energy bands by means of a kicksorter. Two oxygen samples were compared, one being enriched (three times normal), and the other impoverished (0.5 times normal), in O17. Differences between runs with these two gases showed a considerable number of pulses between 1 and 2 Mev., with a maximum at 1.4 Mev. Reasons are given for assigning these pulses to the above reaction, including considerations of the possibility that other exothermic neutron reactions occur. By comparing the number of pulses with the number produced by N14 (n, p) C14 when the chamber contained air, a value of (1.9 ± 0.5) × 10−28 cm.2 for the cross-section for the O17 (n, α) C14 reaction in ordinary oxygen was deduced. This gives a cross-section of (0.46 ± 0.11) × 10−24 cm.2 per atom of the pure isotope O17. The effect measured is about 20% of the total thermal neutron capture cross-section that has been reported for ordinary oxygen.

scholarly journals Measurement of Effective Capture Cross Section of238Np for Thermal Neutrons

2004 ◽  
Vol 41 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Hideo HARADA ◽  
Shoji NAKAMURA ◽  
Toshiyuki FUJII ◽  
Hajimu YAMANA
Keyword(s):  
Cross Section ◽  
Capture Cross Section ◽  
Thermal Neutrons ◽  
Capture Cross

scholarly journals The $^{135}$Cs(n,$\gamma$) cross section at 30 and 500 keV

2021 ◽  
Vol 12 ◽  
pp. 71
Author(s):  
N. Patronis ◽  
P. A. Assimakopoulos ◽  
S. Dababneh ◽  
M. Heil ◽  
F. Kaeppeler ◽  
...  
Keyword(s):  
Cross Section ◽  
Neutron Capture ◽  
Capture Cross Section ◽  
Thermal Neutrons ◽  
Capture Cross ◽  
Neutron Capture Cross Section ◽  
Section Shape ◽  
Pm 10 ◽  
Resolution Mass ◽  
Unstable Isotope

The neutron capture cross section of the unstable isotope $^{135}$Cs was measured relative to that of gold by means of the activation method. The sample was produced by ion implantation in a high resolution mass separator and irradiated with quasi-monoenergetic neutrons at 30 keV and 500 keV, using the $^{7}$Li(p,n)$^{7}$Be reaction. After the irradiations at the above energies, one more irradiation with thermal neutrons was used for defining the sample mass and for measuring the half-life of $^{136}$Cs. The neutron capture cross section was  determined as 164 $\pm$ 10 mbarn and 34.8 $\pm$ 3.0 mbarn at 30 keV and 500 keV, respectively, and were used to normalize the theoretically derived cross section shape.

Sign in / Sign up

Export Citation Format

Share Document