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Instrument measures concentration of small particles in aqueous medium in terms of amount of light scattered and degree to which light transmission is attenuated. Sensitivity to small particles is optimized because both scattered and transmitted illumination levels are detected by photodiodes.
Momentum-velocity analyzer for measuring minute space particles
Observations and an analysis are presented of the micron-sized-particle impacts observed by the plasma-wave instrument aboard the Voyager 2. After a detailed description of signals produced by the dust impacts, the impact noise is interpreted in terms of the number density and mass of the particles. The likely sources of the particles are discussed.
Application of external and laser output mirrors to produce intensified light beam for measurement of light scattered by dispersed particles is described. Use of fiber optics bundles to collect light is discussed. Diagram of equipment and principles of operation are presented.
The accurate determination of dust levels on optical surfaces is necessary to assess sensor system performance. A comparison study was made on several particle measurement methods including those based on direct imaging and light scattering. The effectiveness of removing the particles from the surface prior to determining particle size distributions was also assessed. These studies revealed that some methods, especially those requiring particle removal before analysis, are subject to large systematic errors affecting particle size distributions. Thus, an understanding of the particle measurement methods employed is necessary before any surface cleanliness or obstruction value assignments are accepted as true representations of an optical surface contamination condition.
A delta-doped hybrid advanced detector (HAD) is provided which combines at least four types of technologies to create a detector for energetic particles ranging in energy from hundreds of electron volts (eV) to beyond several million eV. The detector is sensitive to photons from visible light to X-rays. The detector is highly energy-sensitive from approximately 10 keV down to hundreds of eV. The detector operates with milliwatt power dissipation, and allows non-sequential readout of the array, enabling various advanced readout schemes.
A delta-doped hybrid advanced detector (HAD) is provided which combines at least four types of technologies to create a detector for energetic particles ranging in energy from hundreds of electron volts (eV) to beyond several million eV. The detector is sensitive to photons from visible light to X-rays. The detector is highly energy-sensitive from approximately 10 keV down to hundreds of eV. The detector operates with milliwatt power dissipation, and allows non-sequential readout of the array, enabling various advanced readout schemes.
During the ICE flyby of Giacobini-Zinner the plasma wave instrument detected numerous impulsive signals caused by dust impacts on the spacecraft. Most of the impacts occurred within 30,000 km of the comet. The impact rate averaged over the inbound and outbound legs varies approximately as 1/r-squared, as would be expected for an isotropic constant velocity radial outflow. Small differences between the inbound and outbound legs exist which may be indicative of azimuthal variations in the dust production rate. A simple model of the impact ionization and charge collection by the antenna indicates that the particles have a mass on the order of 10 to the -12 to 10 to the -10th gm, corresponding to particles with radii of a few microns.
The impulsive noise that the plasma wave and radio astronomy instruments detected during the Voyager 2 swing by Saturn was attributed to dust grains striking the spacecraft. This report presents a reanalysis of the dust impacts recorded by the plasma wave instrument using an improved model for the response of the electric antenna to dust impacts. The fundamental assumption used in this analysis is that the voltage induced on the antenna is proportional to the mass of the impacting grain. Using the above assumption and the antenna response constants used at Uranus and Neptune, the following conclusions can be reached. The primary dust distribution consists of a 'disk' of particles that coincides with the equator plane and has a north-south thickness of 2-Delta zeta = 962 km. A less dense 'halo' with a north-south thickness of 2-Delta zeta = 3376 km surrounds the primary distribution. The dust particle sizes are of the order of 10 microns, assuming a mass density of 1 g/cu cm. The corresponding particle masses are of the order of 10(exp -9) g, and maximum number densities are of the order of 10(exp -2)/cu m. Most likely, the G ring is the dominate source since the particles were observed very close to that ring, namely at 2.86 R(sub S). Other sources, like nearby moons, are not ruled out especially when perturbations due to electromagnetic forces are included. The calculated optical depth differs by about a factor of 2 from photometric studies. The current particle masses, radii, and the effective north-south thickness of the particle distribution are larger than what Gurnett et al. (1983) reported by about 2, 1, and 1 orders of magnitude, respectively. This is attributed to the fact that the collection coefficient used in this study is smaller than what was used in Gurnett et al.'s earlier publication.
Design and performance of curved photomultiplier tube - effects of structural configuration on dead time and gain stability
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The odd nitrogen source strengths associated with Solar Proton Events (SPEs), Galactic Cosmic Rays (GCRs), and the oxidation of nitrous oxide in the Earth's middle atmosphere from 1974 through 1993 have been compared globally, at middle and lower latitudes (less than 50 deg), and polar regions (greater than 50 deg) with a two-dimensional (2-D) photochemical transport model. As discovered previously, the oxidation of nitrous oxide dominates the global odd nitrogen source while GCRs and SPEs are significant at polar latitudes. The horizontal transport of odd nitrogen, produced by the oxidation of nitrous oxide at latitudes < 50 deg, was found to be the dominant source of odd nitrogen in the polar regions with GCRs contributing substantially during the entire solar cycle. The source of odd nitrogen from SPEs was more sporadic; however, contributions during several years (mostly near solar maximum) were significant in the polar middle atmosphere.
Depending on the mechanism of particle production, the resultant particle size and velocity distribution may range over several orders of magnitude. In general, if particle size information is desired from a given type generator, one must resort to some form of experimental determination of the distribution. If the source of particle production is a dynamic one involving a reasonable volume, holography provides a tailor-made particle size and velocity distribution detector. This is evidenced by the fact that holography allows the entire volume to be recorded on one exposure without any interference with the volume of interest. Herein lies a very important characteristic of the holographic particle detection technique: It provides a holographic nondestructive testing technique in the fullest sense of the definition of nondestructive testing. This report provides a description of three different systems useful in this technique and includes the experimental results from one of the holographic systems which was used to detect particle size and velocity distribution from the Skylab waste tank.
SPEC incorporated designed, built and operated a new instrument, called a pi-Nephelometer, on the NASA DC-8 for the SUCCESS field project. The pi-Nephelometer casts an image of a particle on a 400,000 pixel solid-state camera by freezing the motion of the particle using a 25 ns pulsed, high-power (60 W) laser diode. Unique optical imaging and particle detection systems precisely detect particles and define the depth-of-field so that at least one particle in the image is almost always in focus. A powerful image processing engine processes frames from the solid-state camera, identifies and records regions of interest (i.e. particle images) in real time. Images of ice crystals are displayed and recorded with 5 micron pixel resolution. In addition, a scattered light system simultaneously measures the scattering phase function of the imaged particle. The system consists of twenty-eight 1-mm optical fibers connected to microlenses bonded on the surface of avalanche photo diodes (APDs). Data collected with the pi-Nephelometer during the SUCCESS field project was reported in a special issue of Geophysical Research Letters. The pi-Nephelometer provided the basis for development of a commercial imaging probe, called the cloud particle imager (CPI), which has been installed on several research aircraft and used in More than a dozen field programs.
The characteristics and distribution of the small particles detected by the plasma-wave and radio-astronomy instruments during the Voyager 2 encounter with Uranus in January 1986 are examined. The nature of the observational data and the analysis techniques employed are discussed, and the results are presented in graphs. Particles of rms mass about 2.6 ng and radii of a few microns were found in an impact region of thickness 3840 km, with a maximum number density of 1600/cu m about 280 km from the equatorial plane, shortly after Voyager 2 crossed the plane of the Uranian rings. The possible origin of the particles in the rings or in small satellites outside the rings is considered.
Collaboration with Ames' personnel was in: 1) grant administration, 2) intellectual science support, 3) collaboration with the University of Paris for the Mir flight experiment, and 4) arranging scanning and X-ray probe analytical support from UCB and SUNYP. LNIMS provided access to: 1) analytical research instruments, 2) chemical analyses support, 3) cleanroom facilities, and 4) design and fabrication expertise of hardware and electronics. They also supported the hypervelocity testing along with test data acquisition and its reduction for the breadboard instrument. A&M Associates provided technical expertise and support on determining the expected charges on orbital particles and a conceptual design for a breadboard particle charge detection sensor. University of California provided analytical support for the recovered Mir flight modules using their unique scanning capability to detect particle tracks in the aerogel. SUNYP, along with help from the University of Chicago, analyzed particle tracks found in the aerogel for biogenic compounds using an x-ray probe instrument. Dr. Schultz provided access to his experiments and the benefits of his considerable hyper-velocity testing expertise at the Ames hypervelocity gun facility, and this proved beneficial to our development testing, significantly reducing the test time and cost for the breadboard instrument development testing. The participants in this activity acknowledge and thank the National Aeronautics and Space Administration and its Ames Research Center for providing the necessary support and resources to conduct this investigation on instrument technology for exobiology application and being able to acquire some interesting results. Primarily, the newly identified technology problems for future research are the important results of this research.
There were two principal objectives of the cooperative agreement between NASA and the University of Denver. The first goal was to modify the design of the ER-2 condensation nuclei counter (CNC) so that the effective lower detection limit would be improved at high altitudes. This improvement was sought because, in the instrument used prior to 1993, diffusion losses prevented the smallest detectable particles from reaching the detection volume of the instrument during operation at low pressure. Therefore, in spite of the sensor's ability to detect particles as small as 0.008 microns in diameter, many of these particles were lost in transport to the sensing region and were not counted. Most of the particles emitted by aircraft are smaller than 0.1 micron in diameter. At the start date of this work, May 1990, continuous sizing techniques available on the ER-2 were only capable of detecting particles larger than 0.17 micron. Thus, the second objective of this work was to evaluate candidate sizing techniques in an effort to gain additional information concerning the size of particles emitted by aircraft.
Methods, detectors and systems detect particles and/or measure particle properties. According to one embodiment, a detector for detecting particles comprises: a sensor for receiving radiation scattered by an ensemble of particles; and a processor for determining a physical parameter for the detector, or an optimal detection angle or a bound for an optimal detection angle, for measuring at least one moment or integrated moment of the ensemble of particles, the physical parameter, or detection angle, or detection angle bound being determined based on one or more of properties (a) and/or (b) and/or (c) and/or (d) or ranges for one or more of properties (a) and/or (b) and/or (c) and/or (d), wherein (a)-(d) are the following: (a) is a wavelength of light incident on the particles, (b) is a count median diameter or other characteristic size parameter of the particle size distribution, (c) is a standard deviation or other characteristic width parameter of the particle size distribution, and (d) is a refractive index of particles.