Proportional Technologies

In detectable and isolated thin layers below seismic resolution, phase decomposition can theoretically be used to discriminate relatively high-impedance thin-layer responses from low-impedance reservoir responses. Phase decomposition can be used to isolate seismic amplitudes with a particular phase response or to decompose the seismic trace into symmetrical and antisymmetrical phase components. These components sum to form the original trace. Assuming zero-phase seismic data and normal American polarity, seismically thin layers that are high impedance relative to overlying and underlying half-spaces are seen on the [Formula: see text] phase component, whereas a relatively low-impedance thin layer will appear on the [Formula: see text] phase component. When such phase decomposition is applied to prestack attributes on a 2D line across a thin, 8 m thick, gas-saturated reservoir in the Western Canadian Sedimentary Basin of Alberta, Canada, amplitude-variation-with-angle is magnified on the [Formula: see text] phase component. The [Formula: see text] far-offset component allows the lateral extent of the reservoir to be better delineated. This amplification is also seen on the [Formula: see text] phase component of the gradient attribute. These results are corroborated by seismic modeling that indicates the same phase-component relationships for near- and far-angle stacks as are observed on the real data. Fluid substitution and seismic modeling indicate that, relative to full-phase data, the mixed-phase response observed in this study exhibits variations in fluid effects that are magnified and better observed at far angles on the [Formula: see text] phase component.

The boron-coated straw (BCS) neutron detection technology has been proposed as an attractive 3He replacement solution in a series of applications in homeland security, neutron science, and safeguards. In order to improve the neutron detection efficiency of the BCS, while maintaining manufacturability, Proportional Technologies, Inc. is introducing a modified BCS with significant performance benefits. The proposed pie-like shape consists of any desired number of arc segments, and an equal number of septa walls, which are radially oriented, and extending a desired distance towards the center of the geometry. Each septum is essentially a segment of the wall that has been collapsed onto itself, resulting in a rigid surface, coated on both sides. The area coated on the septa is added to the area coated on the arc segments, thus offering a significant benefit in sensitivity. Compared to a round straw of the same diameter, the coated wall area of the proposed shape with 12 septa is 3 times larger, assuming the septa are equal in length to each of the arc segments. We present laboratory measurements with two prototype detectors that demonstrate stable operation, a neutron sensitivity that is nearly 3 times higher than that measured in a simple BCS with no septa walls, and adequate energy resolution to effectively discriminate against gamma rays.

The limited inventory and minute natural abundance of 3He gas on Earth necessitate the adoption of new technologies for the detection of neutrons, especially in homeland security applications, where large volume deployments are required. We investigate the neutron detection efficiency of a backpack radiation detector based on an unmoderated array of boron-coated straws (BCS). A neutron module was configured that would be light and small enough to fit inside a regular-sized backpack. The module consisted of 36 tubes, arranged in two rows, for a total number of BCS detectors equal to 36 × 7=252. The overall dimensions of the neutron module were 3.18 cm × 26.7 cm × 38.1 cm, and its weight was 1.62 kg (3.57 lbs). The module was fitted immediately inside the back side of the backpack. The detectors are thus very close to the torso of the operator, which, together with a plastic scintillator for gamma detection, act as moderators for high-energy neutrons. In order to maintain a low weight, no other moderating material was installed inside the backpack. The weight of the pack containing both neutron and gamma detector panels, along with foam packing, electronics, and battery, was 5.36 kg (11.8 lbs). The compact dimensions of the design afforded use of a computer style backpack of minimal dimension providing significant additional operational advantages. The testing results indicate that, through use of high-density straw cluster detectors, the proposed design meets both neutron and gamma response government requirements for backpack monitors.

Mobile detection of kilogram quantities of special nuclear materials (SNM) during maritime transportation is a challenging problem for the U.S. Department of Homeland Security. Counting neutrons emitted by the SNM and partitioning them from background neutrons of multiple origins is the most effective passive means of detecting the SNM. Unfortunately, neutron detection, counting, and partitioning in a maritime environment is complex due to the presence of spallation neutrons (commonly known as ship effect) and to the complicated nature of the neutron scattering in that environment. This work studied the possibilities of building a prototype neutron detector using boron- 10 (10B) as the converter in a novel form factor called straws that would address the above problem by examining multiplicity distributions of neutrons originating from a fissioning source. Currently, commercially manufactured fission meters (FM) are available that separate cosmic neutrons from non-cosmic neutrons and quantitatively determine the strength of a fissioning source; however, these FMs use 3He, which is becoming increasingly difficult to procure; also the size and weight of a commercial FM is not conducive to manual neutron detection operations in a maritime environment. The current project may provide a near-term solution to the crisis that has arisen from the global scarcity of 3He by offering a viable alternative to the FM. The prototype detector provides a large-area, efficient, lightweight, more granular neutron responsive detection surface (to facilitate imaging) to ease the application of the new FMs.

BackgroundThe past thirty-five years have seen an intense search for the molecular mechanisms underlying calcium-induced calcium-release (CICR) in cardiac myocytes, with voltage clamp (VC) studies being the leading tool employed. Several VC protocols including lowering of extracellular calcium to affect Ca2+ loading of the sarcoplasmic reticulum (SR), and administration of blockers caffeine and thapsigargin have been utilized to probe the phenomena surrounding SR Ca2+ release. Here, we develop a deterministic mathematical model of a rat ventricular myocyte under VC conditions, to better understand mechanisms underlying the response of an isolated cell to calcium perturbation. Motivation for the study was to pinpoint key control variables influencing CICR and examine the role of CICR in the context of a physiological control system regulating cytosolic Ca2+ concentration ([Ca2+]myo).MethodsThe cell model consists of an electrical-equivalent model for the cell membrane and a fluid-compartment model describing the flux of ionic species between the extracellular and several intracellular compartments (cell cytosol, SR and the dyadic coupling unit (DCU), in which resides the mechanistic basis of CICR). The DCU is described as a controller-actuator mechanism, internally stabilized by negative feedback control of the unit's two diametrically-opposed Ca2+ channels (trigger-channel and release-channel). It releases Ca2+ flux into the cyto-plasm and is in turn enclosed within a negative feedback loop involving the SERCA pump, regulating[Ca2+]myo.ResultsOur model reproduces measured VC data published by several laboratories, and generates graded Ca2+ release at high Ca2+ gain in a homeostatically-controlled environment where [Ca2+]myo is precisely regulated. We elucidate the importance of the DCU elements in this process, particularly the role of the ryanodine receptor in controlling SR Ca2+ release, its activation by trigger Ca2+, and its refractory characteristics mediated by the luminal SR Ca2+ sensor. Proper functioning of the DCU, sodium-calcium exchangers and SERCA pump are important in achieving negative feedback control and hence Ca2+ homeostasis.ConclusionsWe examine the role of the above Ca2+ regulating mechanisms in handling various types of induced disturbances in Ca2+ levels by quantifying cellular Ca2+ balance. Our model provides biophysically-based explanations of phenomena associated with CICR generating useful and testable hypotheses.

US efforts to equip key points of entry with large area neutron detectors to intercept Special Nuclear Materials (SNM) have been undermined by a critical shortage of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He gas. Yearly demand for <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He in US security applications alone is roughly 22,000 liters, exceeding current world supply. Neutron science, safeguards, defense, and other applications that depend on <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He detectors have been severely limited as a result. Alternative neutron detection technologies with large sensitive areas, low gamma sensitivity, and low cost are needed to ensure the long term viability of US detection and interdiction capabilities. We propose a technology based on closely-packed arrays of long, 4 mm diameter, aluminum or copper tubes (straws), internally coated with a thin layer of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B-enriched boron carbide, as a ready replacement for <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He in a variety of detection applications. The high abundance of boron on Earth and low <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B enrichment cost give boron-coated straw (BCS) technology key advantages over <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He detectors. We review three BCS detector configurations including: a large-area neutron-imaging panel, a long range monitor, and a detector module for portal monitors. The imaging panel has 1100 aluminum straws, each 1 m long and 4 mm in diameter. It offers a sensitive area of 1 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , 3D spatial resolution of 7×4×4 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , and can sustain count rates up to 200,000 cps for each of its 22 readout channels without significant loss in resolution. The long-range monitor has 1100 copper straws of similar dimensions and has been subjected to rigorous environmental testing. Finally, the portal monitor design adopts the outer dimensions of currently deployed <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He-based designs, but takes advantage of the small straw diameter to achieve more uniform distribution of neutron converter throughout the moderating material.

In order to fully realize the enhanced potential of the powerful neutron scattering technique provided by high intensity facilities like SNS, large area high rate detectors must be developed that do not depend upon the dwindling stock of 3He. We have developed a neutron detector that offers a large sensitive area (1 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), 3D spatial resolution, high sensitivity and high count rate capability, and it is economical and practical to produce. The detector technology is based on <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B thin film conversion of neutrons in long straw-like gas detectors, as a novel and superior replacement of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He detectors. Twenty-two detector modules, each consisting of 50 straws (1 m long, 4 mm in diameter, natural boron carbide coated), have been constructed and mounted into a robust housing to form a square meter panel detector. Readout electronics including preamplifiers, signal conditioning modules and digitization modules have been designed and tested to meet the required count rate in a 1 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> detector. We have successfully tested the panel detector, by imaging objects of different materials and different shapes. Additionally, one enriched detector module has been fabricated. The enriched module was integrated into the panel and produced a factor of four enhanced sensitivity in agreement with modeling predictions based on five fold higher <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B content. The neutron imaging detector has achieved the required performance for SNS applications and substantially increases performance compared with <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He while utilizing a cheap and inexhaustible conversion medium.

We propose a new radiation detection technology that offers high sensitivity to both gamma rays and neutrons, and can be applied, cost effectively, to survey monitoring. The detector consists of a close-packed array of many small thin- walled copper straws, each 1 m in length, and lined with a very thin (1 mum) coating of enriched boron carbide (10B4C). Gammas are converted in Cu, while thermal neutrons are converted in 10B. The detector design draws upon low-cost technology developed by the high energy physics community for large particle detectors such as ATLAS, currently being commissioned at CERN. The feasibility of the detection technology has been demonstrated previously [1], [2]. The current work presents a unique application of the straw detectors, whereby a rotating panel is used to significantly improve performance. The proposed concept is based on the characteristic signature of a point source, that differentiates it from background noise. We present and evaluate an algorithm for detecting the presence of a source and estimating its net count, direction, and the background rate. Simulation results show that the proposed technique can detect in about 20 minutes time and in an area 100 m in diameter, a 1 mCi gamma ray source, with 90% sensitivity and false alarm probability of 0.1/hour. At 30 min time, 270 g of neutron-emitting 240Pu can be detected within a circular area 100 m in diameter, assuming 20% of neutrons thermalize near the source.

Depth of interaction (DOI) errors in commonly employed crystal detectors cause severe degradation of off-axis resolution in current positron emission tomography (PET) scanners used for small animal or single organ imaging. We propose a PET camera design that uses low cost, easily fabricated, lead-walled straw (LWS) detectors. Photons converted in Pb generate photoelectrons that escape into the straw interior producing an avalanche whose position can be readily measured with high precision. Straws can be of considerable length (up to 50 cm), but small in diameter (2 mm), and can be packed to form scanners with high sensitivity and large fields of view (FOV). The rigorous three-dimensional position encoding eliminates DOI errors encountered in crystal detectors, and provides submillimeter resolution and sensitivity response that is uniform over the full extent of the FOV. We present preliminary results of the operation of a prototype 200-straw module. We then propose a PET scanner design that consists of two rotating trapezoidal detector panels, each panel containing fourteen 200-straw modules (a total of 5600 straws). The FOV has a diameter of 5 cm and extends axially to 15 cm. This unique geometry affords a long field of view, with near constant axial sensitivity of 4.7%, and uniform resolution of 0.9 times 0.9 times 1.0 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> maintained over the entire extent of the FOV, as determined in Monte Carlo simulations.