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 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 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.

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.

The Capture Cross Section of Thermal Neutrons in Water

1956 ◽  
Vol 69 (6) ◽  
pp. 469-479 ◽  
Author(s):  
R E Meads ◽  
C J England ◽  
C H Collie ◽  
G C Weeks
Keyword(s):  
Cross Section ◽  
Capture Cross Section ◽  
Thermal Neutrons ◽  
Capture Cross

The Influence of Instrument Design on Neutron Lifetime Measurements

1975 ◽  
Vol 15 (02) ◽  
pp. 161-168
Author(s):  
Arthur H. Youmans ◽  
Eric C. Hopkinson
Keyword(s):  
Cross Section ◽  
Neutron Capture ◽  
Capture Cross Section ◽  
Thermal Neutrons ◽  
Thermal Neutron Capture ◽  
Neutron Diffusion ◽  
Capture Cross ◽  
Neutron Capture Cross Section ◽  
Neutron Lifetime ◽  
Measurement Interval

Abstract Commercially available logging services provide a measurement of the lifetime of thermal neutrons in formations adjacent to a borehole. This lifetime provides a measure of the macroscopic thermal neutron-capture cross-section S of the formation. which in turn is functionally related to the abundance and constituency of the rock matrix and contained fluids. Because the measurement is extremely sensitive to an abundance of trace elements like boron and gadolinium, it is very difficult to find rock formations with an accurately known value of S, which is required for the accuracy of the measuring system to be experimentally tested. Various theoretical studies published suggest that errors in the determination of S may occur because of the influence of borehole parameters and the effects of neutron diffusion. Experimental results are reported that demonstrate that the design of the instrument is crucial to the validity of any theoretical treatment of the subject. The influence of neutron diffusion and borehole effects can be overcome by optimal selection of spacing and shielding parameters. INTRODUCTION The lifetime of thermal neutrons in formation materials is a measure of the thermal neutron-capture cross-section of the bulk materials comprising the formation. This parameter, S, is quantitatively related to the elemental constituency of the medium. As such, a log based on the measurement of neutron lifetime1 can be used for identifying fluids in porous rocks when there is a contrast between the values of S for the respective fluids. Where formation waters are saline, the log has been used with great success to detect and evaluate oil-bearing zones behind casing. If S is accurately measured, it may be used to compute an unknown parameter with commensurate accuracy using the following relations.2Equation 1 whereEquation 2 The basic assumption of the logging method is that a population of neutrons in a formation will obey the simple relation N = Noe−Svt if the medium is homogeneous. In a medium penetrated by a borehole, it is assumed that the same kind of relation holds true after some time t1:Equation 3 From this equation, the value of S may be derived by measuring N1 and N2 at two times, t1 and t2.Equation 4 This theory requires two assumptions: that neutrons die or disappear only because of capture in the formation, and that it is possible to measure N, the number of live neutrons at any given time (or rather, the ratio of N1 to N2). About 10 years of commercial logging experience have established that S is, to all intents and purposes, accurately and reliably measured3 by the Neutron Lifetime Log (NLL). * This is true even though the foregoing assumptions are not rigorously true. Neutrons do diffuse4 during the measurement interval, with the result that some leave the formation and enter the borehole where their remaining lifetime is dependent on borehole parameters rather than on the formation. Also, the problem of sampling the neutron population is complicated by the fact that the spatial distribution of neutrons changes during the measurement interval, so that any sampling technique designed to measure N is prone to error, or at least subject to doubt.

Sign in / Sign up

Export Citation Format

Share Document