Resonance neutrons

Skinner, J. L. and Trommsdorf, H. P. Proton transfer in benzoic acid crystals A chemical spin-boson problem. Theoretical analysis of nuclear magnetic resonance, neutron scattering, and optical experiments, J.Chem.Phys., 89 (1988), 897-907... 

J. P. Vigier, Theoretical implications of time dependent double resonance neutron interferometry, in W. M. Honig, D. W. Kraft, and E. Panarella (Eds.), Quantum Uncertainties, Recent and Future Experiments and Interpretations. Proc. NATO Advanced Research Workshop on Quantum Violations Recent and Future Experiments and Interpretations, (Bridgeport, CT, June 23-27, 1986) ISBN 0-30-642670-6, Plenum, New York, 1987,... 

For process 3, only slow neutrons of defined energy (25 eV) were effective, making it a typical resonance neutron capture process. Thus it appeared that all three processes were neutron capture, with the effective isotope in all three cases being 238U. 

The physical process of resonance neutron scattering is through the formation of a compound nucleus . Cd, and Gd belong to the small class of nuclei which exhibit a resonance in the thermal energy region. In the case of Cd the compound nucleus Cd will either eject a neutron in an (n, n) process or emit y-rays in an (n, y) process the latter being inelastic. Unlike in X-ray anomalous dispersion, in the present case both the elastic (n, n) and inelastic (n, y) processes contribute to b"(0) ... 

Slow neutrons (neutrons with energies of the order of 1 eV to 1 keV are also called resonance neutrons, because maxima of absorption are observed in this energy range)... 

Neutrons are the most frequently used projectiles for nuclear reactions. As they do not carry a positive charge, they do not experience Coulomb repulsion, and even low-energy (thermal and slow) neutrons can easily enter the nuclei. Neutrons with energies of the order of 1 to lOeV (resonance neutrons) exhibit relatively high absorption maxima. Furthemiore, neutrons are available in large quantities in nuclear reactors with fluxes of the order of about 10 ° to 10 ° cni s . ... 

If the element being determined or a constituent of the sample matrix material has a high capture cross section for thermal or resonance neutrons, possible errors due to self-shielding cannot be ignored. 

The contribution to neutron activation by resonance neutrons alone can be determined by irradiating two identical samples of the element of high cross section, one wrapped in thin cadmium foil. Cadmium is practically opaque to thermal neutrons (o- = 20,000 barns), so that any activity induced in the wrapped sample must be due to neutrons of energies other than thermal... 

Self-shielding of resonance neutrons can be minimized by irradiating in the graphite-loaded column (thermal column) of the pile. Here the contribution by neutrons of energies greater than thermal is considerably reduced. 

The approximation consists in neglecting the formation of Pu by absorption of resonance neutrons from Pu, a procedure justified as long as K4ifYt 04i <7 49044. Wth this approximation Eq. (3.48) reduces to... 

The tetragonal RE, Y, and Sc orthophosphates in particular have been widely used as host media for a variety of solid state chemical, spectroscopic, magnetic resonance, neutron and other studies of rare-earth and actinide impurities. These materials have proved to be ideal hosts for the incorporation of other rare-earth dopants (e.g., Er-doped Lu(P04) for microlaser studies). Doped orthophosphates with desired levels of dopants are desirable for both basic investigations and applications. Unfortunately, there are apparently no available quantitative data on the segregation coefficients for the rare earths in the tetragonal orthophosphates. 

Spectroscopies such as X-ray, 2D nuclear magnetic resonance, neutron diffraction, and inelastic neutron scattering provide a representation of molecular structure in terms of nuclear spatial coordinates and a thermal noise. We shall indicate this set of coordinates with r,, for i = 1, 2,. . . , nuclei, and take its origin at the center of mass. 

This chapter treats principally the vibrational spectra determined by infrared and Raman spectroscopy. The means used to assign infrared absorption bands are outlined. Also, the rationale for the selection of permitted absorption bands is described. The basis for the powerful technique of Fourier Transform Infrared (FTIR) is presented in Appendix 6A. Polyethylene is used to illustrate both band assignment and the application of selection rules because its simple chain structure and its commercial importance have made polyethylene the most thoroughly studied polymer. The techniques of nuclear magnetic resonance, neutron inelastic scattering and ultraviolet spectroscopy are briefly described. The areas of dielectric loss and dynamic mechanical loss are not presented in this chapter, but material on these techniques can be found in Chapters 5. 

Spatial distri But ions of thermal, indium resonance, and fast (E > 1 Mev) neutron flux in the core and in the reflector, particularly the distributions of thermal and indium resonance neutrons in the experimental holes. 

Normalized to nv (thermal) of 1.0 neutron/cB -sec at irenter of lattice. Corrected for absorption of resonance neutrons in cadnium. 

In June, 1941, preliminary work on the absorption of resonance neutrons in spheres of uranium oxide was carried out by Fermi and Anderson together with R. R. Wilson and others of the Princeton group. This work verified the fact that the total absorption could be divided roughly into a surface effect and a volume effect with much higher specific absorption taking place at the surface. 

Since KI melts at 723°C and has an appreciable vapor pressure below that temperature, a substance was sought for use as a monitor which was physically and chemically stable at higher temperatures and became radioactive after resonance-neutron capture with a period not far different from 24.2 min. The material chosen was Ga203, since it is stable and not appreciably volatile at 1200°C, and Ga(w,7) gives a period of 21 min. There is also a period of 14 hours, which introduces a correction, small for short bombardments. 

In an attempt to determine how the actual number of resonance neutrons inside the furnace relative to those outside varied with temperature, caused by the different temperature-dependence of absorption by the carbon and other materials, two types of check experiments were made. At each temperature several bombardments were made of the cyclotron monitor, the 10-cm monitor, and the hot-dish monitor, but with no uranium present, leaving a hole in the graphite where its uranium oxide sphere was otherwise placed. These experiments were not very accurate, but they show that for a given bombardment of the furnace the number of neutrons absorbed by a hot iodine or Ga sample inside the hot furnace is the same within 8 percent as when the furnace is cold. 

Neutron absorption in uranium is believed to be principally of two general types an absorption by U-238, chiefly without fission, in the thermal region and in a resonance region and absorption by U-235 which leads to fission. A detailed knowledge of these absorption processes is of interest in calculating the optimum size and spacing of the spheres to be used in the experiments on the chain reaction. The object of the present series of experiments is the study of the absorption processes in uranium and in particular is the accumulation of data from which can be calculated absorption coefficients for thermal and resonance neutrons. 

The absorption of resonance neutrons was dealt with in a report submitted on June 1, 1941. In that report, Appendix A represented results of measurements carried out at Princeton jointly by the Columbia and Princeton groups on The Capture of Resonance Neutrons by a Uranium Sphere Imbedded in Graphite . Appendix A (written by Fermi and Anderson) arrived at a figure of 4800 cm for the volume of a black body equivalent with respect to resonance absorption to a sphere of 8.5 cm radius containing 9170 gm of UaOg. Appendix... 

B investigated what proportion of the resonance absorption takes place in various portions of the UaOg sphere. It was found that the absorption could be divided into a surface effect and a volume effect. This result made it possible to derive a formula giving the absorbing power for resonance neutrons of UsOg spheres of radii greater than or less than 8.5 cm. 

---