Cross Sections Of Iron Research Articles

Angular Distribution of Neutrons Scattered from Cadmium, Tin, and Bismuth

The differential cross sections for the scattering of 3.7-Mev neutrons from cadmium, tin, and bismuth have been measured over an angular range between 13 degrees and 140 degrees with an angular resolution of about \ifmmode\pm\else\textpm\fi{}10 degrees. The effects due to higher-order scattering have been removed at each measured angle by extrapolation. Previous measurements of the differential cross sections of aluminum, iron, and lead gave a uniform shift of the position of the first minima in the curve with atomic weight. In the present measurements, the curves for cadmium and tin, while quite similar, do not fall uniformly between those of iron and lead. The curve for bismuth, however, is again quite similar to that for lead. Possible explanations of this behavior are discussed in light of the continuum theory of nuclear reactions.

Neutron Polarization

The neutron polarization cross section of iron has been measured as a function of energy from 0.7 to 3.3A by two methods: using the single transmission effect in a block of polycrystalline iron at energies selected by a quartz crystal monochromator; and using a single crystal of magnetized magnetite to analyze the beam emerging from the iron polarizer, the magnetite crystal itself serving as monochromator. The measured values are compared with those of other observers and the theoretically expected values. These are found to agree fairly well within the limits of accuracy of the measurements and existing knowledge of the wave function of the iron $3d$ shell. The two techniques were used also to determine the average polarization (32 percent) as seen by a $\frac{1}{v}$ detector in a beam of reactor neutrons emerging from a 4-cm thick polarizing block of iron. Problems and techniques associated with the measurement of the average polarization of a continuous spectrum are discussed. A simplified experimental treatment of the problem of beam "hardening" is described. A description is given of the use of the magnetic resonance method in conjunction with a single-crystal magnetite analyzer for the measurement of neutron polarization.

Angular distribution of neutrons scattered from cadmium, tin, and bismuth

The differential cross sections for the scattering of 3.7-Mev neutrons from cadmium, tin, and bismuth have been measured over an angular range between 13 degrees and 140 degrees with an angular resolution of about \ifmmode\pm\else\textpm\fi{}10 degrees. The effects due to higher-order scattering have been removed at each measured angle by extrapolation. Previous measurements of the differential cross sections of aluminum, iron, and lead gave a uniform shift of the position of the first minima in the curve with atomic weight. In the present measurements, the curves for cadmium and tin, while quite similar, do not fall uniformly between those of iron and lead. The curve for bismuth, however, is again quite similar to that for lead. Possible explanations of this behavior are discussed in light of the continuum theory of nuclear reactions.

The Scattering of Slow Neutrons by Ferromagnetic Crystals

A beam of filtered neutrons with an average wavelength of 7.0 Å has been used to measure the total cross section of iron as a function of temperature from 290°k to 1170°k. The cross section is found to have a sharp peak at the Curie temperature, 1043°k. At this temperature the measured scattering cross section is 8.6 barns, while the calculated value of the cross section due to nuclear scattering alone is 3.8 barns.

The Inelastic Scattering of Very Slow Neutrons by Iron

The increase with temperature of the total cross section of iron for very slow neutrons has been measured with the help of a cyclotron and a neutron velocity selector. Part at least of this increase is caused by the inelastic scattering associated with lattice vibrations, but the observed rise in cross section is much greater than is predicted by the theory of this effect. It is suggested that a ferromagnetic scattering process may be responsible for the discrepancy

Slow Neutron Velocity Spectrometer Studies. IV. Au, Ag, Br, Fe, Co, Ni, Zn

The spectrometer has been improved, enlarged, and all the operational factors re-evaluated. The principal resonance in gold has been redetermined as ${E}_{0}=4.87\ifmmode\pm\else\textpm\fi{}0.07$ ev, and in silver as 5.13\ifmmode\pm\else\textpm\fi{}0.07 ev. Resonances are found in Br at 35.7, 54, 104, and 136 ev. Transmission dips are also observed at higher energies which are probably due to unresolved levels. The thermal cross section of iron is well matched by the relation $\ensuremath{\sigma}=(11.2\ifmmode\pm\else\textpm\fi{}0.33{E}^{\ensuremath{-}\frac{1}{2}})$. Crystal interference effects are observed in the thermal region with the Debye-Scherrer rings at 2.3A and 2.8A resolved. The cut-off wavelength predicted to be at 4.04A is in good agreement with experiment. No strong resonances are observed in iron at high energies. Resonances are observed in cobalt at 126 ev and 5000 ev. Ni shows crystal interference effects in the thermal region. No strong resonances were detected at high energies. The thermal cross section of Zn is well matched by the relation $\ensuremath{\sigma}=3.85\ifmmode\pm\else\textpm\fi{}0.14{E}^{\ensuremath{-}\frac{1}{2}}$ with crystal interferences effects observed in the thermal region. Resonances in Zn occur at 520 ev, 1100 ev, and 3800 ev.

Double Transmission and Depolarization of Neutrons

Slow neutrons from the chain reacting pile, polarized by passage through highly magnetized iron, have been analyzed by transmission through additional iron (the "double transmission" effect). The large double transmission effects expected from the polarization cross section of iron were obtained only when the magnetic field between polarizer and analyzer was adjusted carefully to obtain non-adiabatic transitions of the neutrons relative to the field. The general methods developed have been used to measure the change in polarization of a neutron beam with passage through unmagnetized iron. The rate of depolarization is a measure of the domain size in the iron and domain sizes have been measured in this way for a number of Armco iron samples of different metallurgical treatment.

The Scattering and Absorption Cross Section of Neutrons in Cobalt

A low voltage neutron source is described which employs the deuteron-deuteron reaction with a continuously renewable target of N${\mathrm{D}}_{4}$Cl. Such a target is formed by subliming N${\mathrm{D}}_{4}$Cl on a metal target cooled with solid C${\mathrm{O}}_{2}$. Neutrons so obtained have been used to study the absorption and scattering cross sections of cobalt. The sum of the absorption and scattering cross sections for cobalt is 26.1\ifmmode\pm\else\textpm\fi{}2.6\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}24}$ ${\mathrm{cm}}^{2}$, and the scattering cross section alone, is for $C$ neutrons 5.6\ifmmode\pm\else\textpm\fi{}1.8\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}24}$ ${\mathrm{cm}}^{2}$, and for $D$ neutrons 3.7\ifmmode\pm\else\textpm\fi{}1.8\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}24}$ ${\mathrm{cm}}^{2}$. The anomalously large scattering cross sections of iron and nickle are thus seen to be independent of their ferromagnetism since the cobalt cross section is essentially normal in magnitude.