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Cremer J.T.,Adelphi Technology, Inc.
Advances in Imaging and Electron Physics | Year: 2013

This chapter covers the correlation, scatter, and intermediate functions of small-angle neutron scatter (SANS). Small-angle X-ray and neutron scatter from general sample materials are covered, followed by the Rayleigh-Gans equation, Babinets' principle, and the differential cross section of X-ray or neutron small-angle scattering from a solute-solvent sample. This provides a resolution of the scattering vector for a SANS instrument for X-rays or neutrons. The chapter also presents neutron scatter length density, particle structure factor, scatter amplitudes, and intensity. The following topics are also covered: random variables, correlation, and independence, followed by derivation of the macroscopic differential cross section for neutron scatter, which involves convolution and cross correlation. Also presented are the coherent and incoherent, elastic and inelastic components of the pair correlation function, intermediate function, and scatter function, the relationships among these functions, and the measured SANS intensities from the neutron scattering sample. The Guinier, intermediate, and Porod regimes of the sample-averaged intermediate function are covered, in addition to the method of contrast variation and Porod's law. Coherent neutron scatter measurements are shown to yield the solute particle size and shape in the Guinier regime, and incoherent neutron scatter measurements are shown to yield the incoherent scatter function, which gives particle diffusion information. Also derived is the principle of detailed balance. Other covered topics are the static approximation, the particle number density operator and pair correlation function, and the moments of the neutron scatter function. The neutron coherent differential cross section in crystals is shown to be expressed by particle density operators, and neutron elastic scatter is shown by the coherent intermediate and scatter functions to occur only in the forward direction for liquids and gases. © 2013 Elsevier Inc. All rights reserved. Source

Cremer Jr. J.T.,Adelphi Technology, Inc.
Advances in Imaging and Electron Physics | Year: 2013

This chapter derives the partial differential cross sections for neutron scatter from a nucleus, which accounts for the neutron spin and the nuclear spin. First covered are the preliminary background topics of angular momentum vectors, spin vectors, and vector operators, the Heisenberg uncertainty principle and commutation of operators, the neutron spin operator, and the neutron spin-lowering and -raising operators. First, the partial differential cross section for nuclear scatter of the neutron spin-up and spin-down states is dervied. Next derived for polarized neutron scatter is the partial differential cross section, which includes both the neutron spin state and nuclear spin state, via the combined neutron spin operator and nuclear spin operators. Covered next are the neutron nuclear scatter length, which accounts for the neutron spin states. Thermal averaging is then taken into account, and the total partial differential cross section for neutron spin state scatter is derived, as well as the neutron spin state scatter lengths for an ensemble of nuclear spins and isotopes. Finally, the partial, differential, and total cross section for neutron coherent and incoherent scatter are derived from an ensemble of atoms of varying nuclear spins and isotopes, which accounts for neutron spin states. © 2013 Elsevier Inc. All rights reserved. Source

Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase I | Award Amount: 100.00K | Year: 2008

A short-pulsed neutron generator is proposed for the detection of concealed high explosives. A recently developed RF-excited plasma neutron generator will be pulsed to produce the activating neutrons whose pulse length is 5-10 ns with a repetition rate of 100 kHz. Using the D-T nuclear reaction, we expect the proposed generator to produce an average yield of 10E9 n/s at this pulse length and rate. In Phase I an existing neutron generator will have a set of electrodes installed to chop the ion beam to produce the desired neutron-pulse time structure and a high peak yield. The present deuterium generator will be redesigned to support the safe use of tritium. The proposed system will be designed to be low cost, transportable, and mechanically and electronically robust, to ensure its wide useage. Unlike penning diode sources, the generator is expected to have a long lifetime. The project has a high probability of success based on the recent development by Adelphi Technology Inc. and Lawrence Berkeley National Laboratory of new RF plasma neutron generators.

Agency: Department of Energy | Branch: | Program: STTR | Phase: Phase II | Award Amount: 750.00K | Year: 2008

No long-lived gamma-ray calibration sources exist with energies above 3.5 MeV, which is an impediment to the calibration of high-purity-germanium and scintillation detectors used in homeland security, nuclear physics and astrophysics. Recent advances in Prompt Gamma-ray Activation Analysis with guided neutron beams have led to the precise calibration of neutron-capture gamma ray sources with energies up to 10.8 MeV. In this project, these neutron-capture gamma ray sources will be produced in a moderator/transducer surrounding a compact, low-yield neutron generator that uses the safe D-D fusion reaction. In Phase I, a portable gamma-ray generator was designed using an inexpensive ion source, a self-replenishing target for generating neutrons, and a compact moderator with a gamma-ray transducer. The parameters for selecting the three major components were based on the required count rate for calibrating the frequency and efficiency of the detector, while still ensuring operator safety and minimizing possible damage to the detector. The high-energy gamma ray spectrum was measured using the selected transducer material. In Phase II, the ion source will be fabricated and tested, and the fast neutron generator will be fabricated and integrated into the moderator and gamma ray emitter. Then, the source¿s gamma-ray yield will be measured, and the source¿s safety and benefits for detector calibration will be determined. Commercial Applications and Other Benefits as described by the awardee: The DOE and the International Atomic Energy Agency must provide for the application of standards for the safety of nuclear installations and radioactive sources. The new device should enable the easy calibration of the energy and efficiency of HPGe detectors at high gamma ray energies, at in-house installations or in the field, for the identification of nuclear and radioactive materials. It also should reduce security concerns about the storage of radioactive sources currently in use.

Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 100.00K | Year: 2008

Refractive lenses can dramatically improve neutron instrumentation in DOE facilities. In previous experiments, compound refractive lenses (CRLs) were shown to be capable of imaging using thermal neutrons. However, a number of problems exist that prevent the full implementation of these lenses: the initial prototype lenses, which used compression molding of metals, have long focal lengths, small fields of view, poor surface quality, and material inhomogeneities. To achieve shorter focal lengths and shorter neutron wavelengths, the radii of curvature must be reduced. This project will use an injection-molding bubble injection process to design and fabricate refractive lenses that will be able to focus, collimate, and image thermal neutrons. Both simple concave and Fresnel lenses will be investigated. Commercial Applications and other Benefits as described by the awardee: The new CRLs should provide better resolution and higher quality images. They will be inexpensive, compact, and capable of imaging using thermal neutrons with wide bandwidth spectra. Since CRLs should have very modest cost, they would be much less expensive than the large mirrors and other optics currently used. Many scientific and technological applications should ensue, including microscopy, scattering, interferometry, crystallography, and reflectometry.

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