R.E. Morgado
Los Alamos National Laboratory
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Featured researches published by R.E. Morgado.
Journal of Energetic Materials | 1986
Tsahi Gozani; R.E. Morgado; Chris Seher
Abstract The status of bulk explosive detection techniques based on nuclear interrogation methods is reviewed. The desirable characteristics of an operational system capable of meeting the requirements for civil aviation security are compared with what can be expected from nuclear-based techniques. The comparison is limited to those techniques that utilize penetrating neutron and photon probes on the target elements of explosives most likely to be encountered in the airport scenario. The physical properties of a relevant group of explosives are surveyed for unique characteristics that could provide detectable signatures to nuclear-based techniques. A survey of the accessible reactions and their relative detection sensitivities are tabulated for a selection of practical interrogating probes. Some results obtained with systems currently under development are reported.
X-Ray Spectrometry | 1997
J.F.C.A. Veloso; J.M.F. dos Santos; C.A.N. Conde; R.E. Morgado
Performance characteristics of a microstrip gas counter operated as an x-ray fluorescence spectrometer are reported. Gas amplification as a function of microstrip anode-cathode voltage was measured, and the breakdown threshold voltage was determined in pure xenon. The detector temporal stability and the effect of gas purity were assessed. Energy resolution and linearity, detection efficiency and uniformity of spatial response in the 2-60 keV x-ray energy range were determined from the pulse-height distributions of the fluorescence x-ray spectra induced in a variety of single- and multi-element sample materials. Energy resolution similar to that of conventional proportional counters was achieved at 6 keV.
ieee nuclear science symposium | 1996
J. A. M. Lopes; J.M.F. dos Santos; C.A.N. Conde; R.E. Morgado
A xenon gas proportional scintillation counter has been instrumented with a novel photosensor that replaces the photomultiplier tube normally used to detect the VUV secondary scintillation light. In this implementation, the collection grid of a planar gas proportional scintillation counter also functions as a multiwire proportional chamber to amplify and detect the photoelectrons emitted by a reflective CsI photocathode in direct contact with the xenon gas. This integrated concept combines greater simplicity, compactness, and ruggedness (no optical window is used) with low power consumption. An energy resolution of 12% was obtained for 59.6 keV X-rays.
IEEE Aerospace and Electronic Systems Magazine | 1989
Tsahi Gozani; Peter Ryge; Patrick M. Shea; Chris Seher; R.E. Morgado
Nuclear-based techniques for the detection of bulk explosives are described. These techniques are shown to provide the only feasible approach for meeting the operational criteria of high throughput of screening luggage and cargo against concealed explosives in air transportation. The nuclear-based techniques are characterized by probing the screened object (e.g. luggage) with highly penetrating radiation, i.e. neutrons or energetic gamma rays. High-energy gamma rays produced by the probing radiation are characteristic to the elemental composition of the objects. The gamma rays are detected by an array of detectors placed near the object. The intensity, energy, and spatial distribution of the detected radiation and their relationship to the primary radiation allow a computer to determine the presence or absence of explosives. The nature of neutron interactions, the gamma detectors used, and the data analysis on which the decision is based are discussed. >
ieee nuclear science symposium | 1997
J.M.F. dos Santos; A.J.V.D. Soares; C.M.B. Monteiro; R.E. Morgado; C.A.N. Conde
The curved-grid technique was developed to maintain the superior performance of large-area gas proportional scintillation counters (GPSCs) without resorting to complex and bulky focusing systems or large photomultiplier tubes (PMTs) for applications in energy-dispersive X-ray fluorescence analysis. The technique is a simple method to compensate for the variation in solid angle viewed by the PMT as a function of the radial distance from the cylindrical axis of the detector. The feasibility of the technique is demonstrated in a GPSC, by measuring the energy resolution as a function of entrance window diameter. With a properly shaped curved grid, no degradation in detector energy resolution is observed even when the effective detector sensitive area is increased approximately six-fold. The maximum ratio of detector entrance window to PMT diameter achieved thus far is approximately 0.75.
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment | 2003
J. A. M. Lopes; L.M.P. Fernandes; J.M.F. dos Santos; R.E. Morgado; C.A.N. Conde
The response of a Peltier-cooled large-area avalanche photodiode to VUV-light is investigated as a function of the operation temperature. The reduction of the temperature down to 5°C will improve both photodiode light-level detection limit and statistical fluctuations; further temperature reduction will not result in improved performance. Optimum operation characteristics are already achieved for gains around 100 and do not depend significantly on the operation temperature. The relative variation of the gain with temperature increases with the biasing voltage presenting values that are almost a factor of two higher than for visible light detection.
IEEE Transactions on Nuclear Science | 2000
J. A. M. Lopes; J.M.F. dos Santos; R.E. Morgado; C.A.N. Conde
The application of recently developed VUV silicon photodiodes as a replacement for the standard photomultiplier tube (PMT) in a gas proportional scintillation counter (GPSC) is investigated. A photodiode positioned within the gas envelope would result in a GPSC that is more compact, robust, and simpler to operate. At the 170 nm wavelength of the scintillation light from xenon, UV photodiodes achieve an effective quantum efficiency of 72%, better than the typically 20% figure for PMTs. On the other hand, the lack of amplification in the photodiode readout limits the signal-to-noise ratio that can be achieved. A GPSC based on a silicon photodiode with an active area of 100 mm/sup 2/ and no additional amplification stage achieved energy resolutions of 20.5, 14.5 and 13.4% for 5.9, 22.1, and 59.6 keV X-rays, respectively. Signal noise in the low energy limit extends up to approximately 3 keV.
Applied Radiation and Isotopes | 2000
J.M.F. dos Santos; C.M.B. Monteiro; R.E. Morgado; C.A.N. Conde
Non-linearities in the energy response of gas detectors in the regions of the absorption edges of the detection medium are well documented. Monte Carlo calculations show that the non-linearity results from differences in efficiencies for converting absorbed radiation into ionisation for different atomic sub-shells. Energy non-linearity in germanium-based solid-state detectors in the region of the germanium 11.104-keV K-edge is not well documented, although a 1% non-linearity has been previously reported in a Ge(Li) detector. This relatively high value is of practical concern since high-purity germanium (HPGe) is often the detector of choice for alpha- and X-ray spectrometry down to a few keV. In this paper, we present the experimental results for the energy response of a HPGe detector in the 8-15-keV energy region of the germanium K-edge. Within the accuracy of our measurements, we conclude that there is no measurable non-linearity effect in germanium at the K-edge.
IEEE Transactions on Nuclear Science | 1996
T.H.V.T. Dias; F.P. Santos; J.M.F. dos Santos; J. A. M. Lopes; J.F.C.A. Veloso; P.J.B.M. Rachinhas; R.E. Morgado; A.D. Stauffer; C.A.N. Conde
We have observed that the pulse-height distributions of X-ray events that deposit essentially the same amount of energy in a xenon gas detector will vary according to the deexcitation pathways available to the photoionized atoms. A xenon gas proportional scintillation counter was used to compare the pulse-height distributions of events in which fluorescence X-rays from xenon escape detection. Experimental results are presented and the behaviour for different types of events is clarified using Monte Carlo simulation. The results indicate that particular care must be taken when using escape peaks for energy calibration of xenon gas detectors.
Substance Identification Technologies | 1994
R.E. Morgado; C. C. Cappiello; M. P. Dugan; C. A. Goulding; Samual Dean Gardner; C.L. Hollas; B. L. Berman; Robert W. Hamm; K. R. Crandall; J. M. Potter; Ronald A. Krauss
We describe a method for performing nuclear resonance absorption with the proton beam from a radio frequency quadrupole (RFQ) linear accelerator. The objective was to assess the suitability of the pulsed beam from an RFQ to image nitrogen relative to that of electrostatic accelerators. This choice of accelerator results in tradeoffs in performance and complexity, in return for the prospect of higher average current. In spite of a reduced resonance attenuation coefficient in nitrogen, we successfully produced 3D tomographic images of real explosives in luggage the first time the unoptimized system was operated. The results and assessments of our initial laboratory measurements are reported.