Whole-Field Measurements in Gas-Phase Turbulent Flows

The purpose of this experimental, nine-month effort was to investigate the scalar field in fully-developed, gas-phase, turbulent flows, using planar index-of-refraction imaging at elevated pressures (p ≃ 10 atm). The motivation behind this work is to further our understanding of phenomena that rely on the behavior of scalar gradients, such as aero-optic effects, laser propagation through, and scattering by, gas-phase turbulent flows, as well as turbulent mixing and combustion. In this effort, we have used planar laser-Rayleigh scattering to image simultaneously the index-of-refraction field of a turbulent jet and the optical degradation of the planar laser probe beam caused by the turbulent flow-field. From these results, we have demonstrated that conducting these experiments at elevated pressure increases the index-of-refraction gradients and improves the signal-to-noise ratio over measurements conducted at atmospheric conditions. The optical degradation occurs in the jet-fluid region and manifests itself as a spatial amplitude modulation (streaks) in the laser sheet. This optical degradation illustrates the same loss of coherence undergone by laser beams and by coherent information when propagating through the turbulent atmosphere

Miniature Laser Doppler Velocimeter for Measuring Wall Shear

A miniature optoelectronic instrument has been invented as a nonintrusive means of measuring a velocity gradient proportional to a shear stress in a flow near a wall. The instrument, which can be mounted flush with the wall, is a variant of a basic laser Doppler velocimeter. The laser Doppler probe volume can be located close enough to the wall (as little as 100 micron from the surface) to lie within the viscosity-dominated sublayer of a turbulent boundary layer. The instrument includes a diode laser, the output of which is shaped by a diffractive optical element (DOE) into two beams that have elliptical cross sections with very high aspect ratios

An imaging neutron/gamma-ray spectrometer

We present the test results of a neutron/gamma-ray imaging spectrometer for the identification and location of radioactive and special nuclear materials. Radioactive materials that could be fashioned into a radiation dispersal device typically emit gamma rays, while fissile materials such as uranium and plutonium emit both neutrons and gamma rays via spontaneous or induced fission. The simultaneous detection of neutrons and gamma rays is a clear indication of the presence of fissile material. The instrument works as a double-scatter telescope, requiring a neutron or gamma ray to undergo an interaction in two detectors to be considered a valid event. While this requirement reduces the detector efficiency, it yields information about the direction and energy of the incident particle, which is then used to reconstruct an image of the emitting source. Because of this imaging capability background events can be rejected, decreasing the number of events required for high confidence detection and thereby greatly improving its sensitivity. The instrument is optimized for the detection of neutrons with energies from 1-20 MeV and gamma rays from 0.4 to 10 MeV. Images and energy spectra for neutron and gamma rays are reported for several sources including depleted uranium and plutonium. In addition, the effect of neutron source shielding is investigated

An imaging neutron/gamma-ray spectrometer

We present the design and development of a dual-species, neutron/γ-ray imaging spectrometer for the identification and location of radioactive and special nuclear materials (SNM). Real-time detection and identification is important for locating fissile materials. These materials, specifically uranium and plutonium, emit neutrons and γ rays via spontaneous or induced fission. Co-located neutron and γ-ray emissions are a sure sign of fissile material, requiring very few spatially correlated events for a significant detection. Our instrument design detects neutrons and γ rays from all sources in its field of view, constructs images of the emission pattern, and reports the spectra for both species. The detection principle is based upon multiple elastic neutron-proton scatters in organic scintillator for neutrons, and Compton scattering in organic scintillator followed by photoelectric absorption in inorganic scintillator for γ rays. The instrument is optimized for neutron imaging and spectroscopy in the 1-20 MeV range. We recorded images and spectra of a Cf-252 source from 0.5 - 10 MeV, and have done similarly for several γ-ray sources. We report the results of laboratory testing of this expanded instrument and compare them to detailed Monte Carlo simulations using Geant4

A portable neutron spectroscope (NSPECT) for detection, imaging and identification of nuclear material

We have developed, fabricated and tested a prototype imaging neutron spectrometer designed for real-time neutron source location and identification. Real-time detection and identification is important for locating materials. These materials, specifically uranium and transuranics, emit neutrons via spontaneous or induced fission. Unlike other forms of radiation (e.g. gamma rays), penetrating neutron emission is very uncommon. The instrument detects these neutrons, constructs images of the emission pattern, and reports the neutron spectrum. The device will be useful for security and proliferation deterrence, as well as for nuclear waste characterization and monitoring. The instrument is optimized for imaging and spectroscopy in the 1-20 MeV range. The detection principle is based upon multiple elastic neutron-proton scatters in organic scintillator. Two detector panel layers are utilized. By measuring the recoil proton and scattered neutron locations and energies, the direction and energy spectrum of the incident neutrons can be determined and discrete and extended sources identified. Event reconstruction yields an image of the source and its location. The hardware is low power, low mass, and rugged. Its modular design allows the user to combine multiple units for increased sensitivity. We will report the results of laboratory testing of the instrument, including exposure to a calibrated Cf-252 source. Instrument parameters include energy and angular resolution, gamma rejection, minimum source identification distances and times, and projected effective area for a fully populated instrument