Gamma-ray Sensor Research Articles

PROPERTIES OF TREATMENT SLUDGE DURING SEDIMENTATION AND CONSOLIDATION TESTS

Sedimentation and consolidation tests have been conducted on sludge produced from an acid mine drainage (AMD) treatment plant. The testing program involved the development of a new laboratory system, designed and constructed to assess the specific properties of low density slurry. During the instrumented large size column tests, the evolution of sedimentation and hydrodynamic consolidation was monitored with optical observation of the solidliquid interface, evaluation of density ρ with gamma ray sensors, and measurement of pore pressure u using transducers. At the end of each test, physical and geotechnical properties of the resulting sludge were measured. In this paper, the authors will present a brief overview of the set up, followed by a presentation of new test results with the analysis using sedimentationconsolidation theories. The results presented here will be used in future analyses to evaluate the volume changes of AMD treatment sludge in storage basins. Additional

Multimodality tomography for multiphase hydrocarbon flow measurements

Multimodality sensing is used for monitoring of multiphase hydrocarbon flow where there is a need to measure the quantity of oil, water and gas in a cross section of a pipe originating from an oil well. Information on the flow regime, i.e., the physical distribution of the hydrocarbon production constituents in the pipe cross section, is demanded. Expedient information concerning the productivity of the well, i.e., the quantity of oil, water and gas produced, the transport of multiphase flow and the upstream separation process can be provided by tomographic information. A dual modality tomograph (DMT), consisting of capacitance and gamma-ray sensors, has been developed at the University of Bergen. Characterization of the DMT has demonstrated feasibility in relation to the hydrocarbon flow application, but also shortcomings mainly relating to the performance of the capacitance sensor in water continuous phase, and the salinity dependence of the gamma-ray measurements. Research work has been conducted to further develop the DMT for hydrocarbon multiphase flow. The new developments include dual modality densitometry (DMD), where both mixture density and salinity are measured, and a water-cut independent high-frequency magnetic field sensor.

High-speed data acquisition and digital signal Processing system for PET imaging techniques applied to mammography

This paper is framed into the Positron Emission Mammography (PEM) project, whose aim is to develop an innovative gamma ray sensor for early breast cancer diagnosis. Currently, breast cancer is detected using low-energy X-ray screening. However, functional imaging techniques such as PET/FDG could be employed to detect breast cancer and track disease changes with greater sensitivity. Furthermore, a small and less expensive PET camera can be utilized minimizing main problems of whole body PET. To accomplish these objectives, we are developing a new gamma ray sensor based on a newly released photodetector. However, a dedicated PEM detector requires an adequate data acquisition (DAQ) and processing system. The characterization of gamma events needs a free-running analog-to-digital converter (ADC) with sampling rates of more than 50 Ms/s and must achieve event count rates up to 10 MHz. Moreover, comprehensive data processing must be carried out to obtain event parameters necessary for performing the image reconstruction. A new generation digital signal processor (DSP) has been used to comply with these requirements. This device enables us to manage the DAQ system at up to 80 Ms/s and to execute intensive calculi over the detector signals. This paper describes our designed DAQ and processing architecture whose main features are: very high-speed data conversion, multichannel synchronized acquisition with zero dead time, a digital triggering scheme, and high throughput of data with an extensive optimization of the signal processing algorithms.

Novel X- and gamma-ray sensors based on bulk-grown silicon-germanium

In this brief, preliminary experimental results and the theoretical assessment of various compositions of bulk-grown, single-crystal silicon-germanium (SiGe) for application in X- and gamma-ray sensors, are presented. It is shown that the absorption efficiency of Si/sub 1-x/Ge/sub x/ sensors is significantly superior to that of silicon sensors, even for relatively low germanium concentrations, while the bandgap narrowing should be sufficiently small not to restrict the device operation to cryogenic temperatures, as in the case of pure germanium detectors. The experimental results obtained with PIN-like devices manufactured on Si/sub 0.95/Ge/sub 0.05/ indicate suitable hole mobility, and superior detection efficiency for X-ray photons.

Locating radiation hot spots on the ground with a gamma-ray directional sensor

This paper reports on an experimental investigation to determine the feasibility of locating radiation hot spots within an area of contamination on the ground that contains radionuclides. The detecting and locating sensor is carried in a helicopter that can rapidly scan large areas of contamination for hot spots. A scintillation type of gamma-ray directional sensor (GRDS) was used in this study. Previous work showed that a GRDS could detect and accurately locate stationary point and broad sources of gamma-rays or X-rays by rotating a GRDS in the field of radiation. In this present study, the sensor was stationary but the radiation source was moving pass the sensor. This technique simulated a helicopter flying over an area of contamination on the ground and scanning the area for hot spots with a sensor that is fixed in position on board the helicopter. The experimental approach generated data that established the operational limitations of the helicopter's speed, height, and the intensity of the hot spot relative to the GRDS's sensitivity. The results show that a GRDS sensor in a helicopter can locate cesium-137 hot spots on the ground. Hot spots with an activity of about 0.3 Ci can be located from a helicopter moving with a speed of 44.7 m/s at a height of 62.5 m.

ANTS in space?

Inspired by the accomplishments of social insects, and perhaps disappointed by the failures of conventional robots, NASA is planning to send a swarm of miniature spacecraft to explore the Asteroid Belt. The collective intelligence of the swarm – to be composed of hundreds of tiny, independent spacecraft called ANTS (‘Autonomous Nano Technology Swarm’) – will be based on that of earthbound species, such as ants and wasps. After traveling to the Asteroid Belt, the ANTS will assume different roles: some will act as rulers, others as messengers, but most will be workers. Each worker will carry a single instrument, such as a magnetometer or a gamma-ray sensor, and will perform a single specified task. The collective nature of the swarm is supposed to make the system robust: the loss of a few spacecraft will not cripple the mission. By performing their tasks individually but later swapping knowledge, the ANTS will behave as a single, extended organism, more intelligent that the sum of its parts. Perhaps the real challenge is whether the same be said of the NASA research group… MW

DUET MULTIPHASE FLOW METER

CSIRO Minerals has developed a Multiphase Flow Meter (MFM) for measuring oil, water and gas flow rates in offshore topside and sub-sea oil production pipelines. In 1997 Kvaerner Oilfield Products (KOP) signed an exclusive licence agreement with CSIRO Minerals for production and further development of the dual energy gamma-ray transmission (DUET) MFM. This new technology has the potential to save the oil industry many millions of dollars in capital, operating and maintenance costs. Essentially, the MFM consists of two specialised gamma-ray transmission gauges, pressure and temperature sensors, which are mounted on a pipe spool carrying the full flow of the well stream, and processing electronics. Measurements of the intensities of transmitted gamma rays are made to infer the proportions of oil, water and gas, and flow velocities are determined from cross-correlation of gamma-ray signals.Prototype MFM's have completed several Australian and overseas trials, including an extended four-year trial (1994–1998) on Esso's West Kingfish platform in Bass Strait and Texaco's test loop facility in Humble, Texas. During these and other trials the MFM has determined water cut to accuracies of 2–4%, and liquid and gas flow to accuracies of 5–10%, up to a gas volume fraction (G VF) of 95%. Full production versions of the MFM are presently under construction by KOP, and the first installation is due to take place early in 2000 at Texaco's Captain oilfield in the North Sea. CSIRO Minerals is presently consulting with the Australian oil industry to assess interest in the development of a wet gas MFM, capable of operating at GVF's in excess of 95%

Conductivity effects in hydrogenated amorphous silicon induced by gamma-ray irradiation

Hydrogenated amorphous silicon films 0.45 and 1.12 μm thick, grown by RF glow discharge plasma PECVD on Corning-7059 glass, were irradiated by a 60Co source (activity 2.8 × 10 15 Bq) in the dose range 10–450 kGy at different dose rates. The dark current of the samples, under 100 V applied voltage, was measured before, during and after gamma irradiation. When the irradiation starts, the dark current increases up to a level linearly dependent on the dose rate. When the irradiation is switched off, the dark current returns close to the initial value in a few days. Such behaviour suggests a possible application of hydrogenated amorphous silicon films in dosimetry and as gamma ray sensors. Moreover, the film optical constants were computed from the transmittance spectra measured in the range 500–2500 nm, before and after irradiation. After irradiation, the film optical absorption is slightly increased and the energy gap is substantially unchanged.

A study of positrons from Soviet nuclear powered satellites as tracers for magnetospheric research

Two Soviet satellites carrying nuclear reactors operated in circular 790 km orbits (65° inclination) in 1987 and 1988. Positrons generated in the satellites' surfaces by the intense reactor gamma radiation escaped and were trapped for periods of minutes to hours in the geomagnetic field. These positrons have been observed on many occasions by gamma ray sensors on the SMM satellite (in 500 km orbit) which identify the positrons by the 511 keV gamma rays created when they annihilate in the satellite surface. The SMM detector provides a time resolution of 64 milliseconds. It has recorded positron rise-times of less than 0.5 second (corresponding to a satellite travel distance of about 1 positron gyroradius) on many occasions as it encounters the low-L edge of positrons injected by the Soviet satellites as far as half-way around the earth. We are studying the potential of these sharply defined positron shells as magnetospheric tracers and as a means for examining particle diffusion and loss processes.

Coal mining applications of CdTe gamma ray sensors

Cadmium telluride (CdTe) solid-state radiation detectors have been used in the development of instrumentation that improves the efficiency of coal-mining operations by helping to locate coal seams and preventing the mining of high-sulfur coal near the edges of the seam. CdTe detectors were selected for these applications because while they are small and durable, they offer good stopping power, deliver adequate spectral response and operate at low voltage. These CdTe-based instruments have passed the mine-safety standards and are now in operation in the mine.

Formation Evaluation: Benefits of Downhole Logging While Drilling: ABSTRACT

The development of new downhole measurement systems, coupled with mud-pulse telemetry techniques, allows real time surface evaluation of downhole parameters while drilling. Currently available systems, such as Exploration Logging's DLWD tool, combine formation resistivity and natural gamma ray sensors with directional survey and other measurements. These parameters aid formation evaluation, pressure evaluation, well-bore positioning, and drilling efficiency. For real time applications, such as correlation and bed identification, a DLWD log can be treated as a conventional wireline log. For further evaluation, the interpretation of DLWD data requires an understanding of the differences in the design of MWD tools compared to conventional wireline tools, as well as the differences in logging environment. These differences, include physical size, logging speed, borehole effects, invasion, etc. The benefits of real time subsurface data enhance other geologic and engineering data acquisition systems in formation evaluation, pressure evaluation, and well planning. End_of_Article - Last_Page 560------------

High-precision source location of the 1978 November 19 gamma-ray burst

The celestial source location of the November 19, 1978, intense gamma ray burst has been determined from data obtained with the interplanetary gamma-ray sensor network by means of long-baseline wave front timing instruments. Each of the instruments was designed for studying events with observable spectra of approximately greater than 100 keV, and each provides accurate event profile timing in the several millisecond range. The data analysis includes the following: the triangulated region is centered at (gamma, delta) 1950 = (1h16m32s, -28 deg 53 arcmin), at -84 deg galactic latitude, where the star density is very low and the obscuration negligible. The gamma-ray burst source region, consistent with that of a highly polarized radio source described by Hjellming and Ewald (1981), may assist in the source modeling and may facilitate the understanding of the source process. A marginally identifiable X-ray source was also found by an Einstein Observatory investigation. It is concluded that the burst contains redshifted positron annihilation and nuclear first-excited iron lines, which is consistent with a neutron star origin.

A study of fast time structure within cosmic gamma-ray bursts

view Abstract Citations (12) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A study of fast time structure within cosmic gamma-ray bursts. Imhof, W. L. ; Nakano, G. H. ; Johnson, R. G. ; Kilner, J. R. ; Reagan, J. B. ; Klebesadel, R. W. ; Strong, I. B. Abstract Two gamma-ray bursts are studied on the basis of data recorded by a germanium spectrometer on board a low-altitude polar orbiting satellite and by gamma-ray sensors on board the Vela satellite. For the event of Dec. 18, 1972, the data indicate that at least five microbursts occurred within 1.8 sec. There is also evidence for three more time-structured features at later times. The spectrum showed a generally increasing hardness at the beginning of the event, but during microbursts, when the intensities were higher, the spectra did not differ significantly from those at neighboring times. The spectra at late times were much softer than those observed just prior to the main burst. For the December, 1972 event and for the event of July 21, 1973, the occurrence of microbursts was observed at various times throughout the events. The microburst structure of the July event was even more pronounced than in the December event. Publication: The Astrophysical Journal Pub Date: June 1975 DOI: 10.1086/153649 Bibcode: 1975ApJ...198..717I Keywords: Cosmic Rays; Fine Structure; Gamma Rays; Satellite Observation; Time Dependence; Black Body Radiation; Germanium; Polar Orbits; Radiation Measurement; Scintillation Counters; Spectrometers; Vela Satellites; Space Radiation full text sources ADS |

The Mystery of the Cosmic Gamma-Ray Zaps

The Mystery of the Cosmic Gamma-Ray Zaps