Showing papers in "IEEE Transactions on Nuclear Science in 1974"
TL;DR: The authors compare the Fourier algorithm and a search algorithm using a simulated phantom to speed the search algorithm by using fewer interactions leaves decreased resolution in the region just inside the skull which could mask a subdural hematoma.
Abstract: The Fourier reconstruction may be viewed simply in the spatial domain as the sum of each line integral times a weighting function of the distance from the line to the point of reconstruction A modified weighting function simultaneously achieves accuracy, simplicity, low computation time, as well as low sensitivity to noise Using a simulated phantom, the authors compare the Fourier algorithm and a search algorithm The search algorithm required 12 iterations to obtain a reconstruction of accuracy and resolution comparable to that of the Fourier reconstruction, and was more sensitive to noise To speed the search algorithm by using fewer interactions leaves decreased resolution in the region just inside the skull which could mask a subdural hematoma
2,100 citations
TL;DR: Algebraic reconstruction techniques (ART) were introduced by Gordon et al. as mentioned in this paper for solving the problem of 3D reconstruction from projections in electron microscopy and radiology, where each projected density is thrown back across the higher dimensional region from whence it came, with repeated corrections to bring each projection of the estimate into agreement with the corresponding measured projection.
Abstract: Algebraic reconstruction techniques (ART) were introduced by Gordon et al. (1970) for solving the problem of three dimensional reconstruction from projections in electron microscopy and radiology. An X-ray photograph represents the projection of the three-dimensional distribution of X-ray densities within the body onto a two-dimensional plane. A finite number of such photographs taken at different angles allows one to reconstruct an estimate of the original 3-D densities. The ART algorithms for solving this problem have a simple intuitive basis. Each projected density is thrown back across the higher dimensional region from whence it came, with repeated corrections to bring each projection of the estimate into agreement with the corresponding measured projection.
449 citations
TL;DR: In this paper, the authors present application of methods of ascertaining the threedimensional distribution of isotope concentration or density in nuclear medicine, and differ from previous three-dimensional reconstruction efforts of astrophysics, electron microscopy, and X-ray radiology in that statistically poor measurements and photon attenuation are taken into account by the algorithm.
Abstract: The study presents application of methods of ascertaining the three-dimensional distribution of isotope concentration or density in nuclear medicine, and differs from previous three-dimensional reconstruction efforts of astrophysics, electron microscopy, and X-ray radiology in that statistically poor measurements and photon attenuation are taken into account by the algorithm. The methods discussed are applicable to photon or heavy ion transmission radiography as well as emission imaging.
290 citations
TL;DR: In this article, an analysis of signal, noise and position resolution relations for some of the most interesting position-sensing methods is presented, and a new method for terminating transmission lines and for "noiseless" damping which employs a capacitance in feedback is presented.
Abstract: An analysis is presented of signal, noise and position resolution relations for some of the most interesting position-sensing methods. "Electronic cooling" of delay line terminations is introduced in order to reduce noise in the position-sensing with delay lines. A new method for terminating transmission lines and for "noiseless" damping which employs a capacitance in feedback is presented. It is shown that the position resolution for the charge division method with resistive electrodes is determined only by the electrode capacitance and not by the electrode resistance, if optimum filtering is used.
273 citations
TL;DR: In this article, a modified version of a previously studied algorithm was used to reconstruct the attenuation coefficients of a simulated head section from x-ray transmission measurements, which was then used to perform absolute measurements of attenuation coefficient at points interior to the skull.
Abstract: Several algorithms have been proposed for reconstructing the variable attenuation coefficients of tissues inside the skull from x-ray transmission measurements. We show that a simulated head section is accurately reconstructed by a modification, which is both fast and simple, of a previously studied algorithm. The possibility of using the algorithm to perform absolute measurements of the attenuation coefficient at points interior to the skull is high.
270 citations
TL;DR: In this paper, a model which considers the effects of deep acceptors which slowly ionize (~103 s) to an equilibrium concentration ~5 × 1011/cm3 can explain the changes of pulse shape, pulse amplitude, capacitance, energy resolution, and?-ray efficiency with time.
Abstract: Nuclear radiation detectors made from high resistivity chlorine doped cadmium telluride grown by the travelling heater method were evaluated. Short term performance for ?, s, and ? radiations was good but the long term performance (>1 min) was degraded by a decrease in the full energy pulse height and ?-ray efficiency with time after the bias voltage was applied. A model which considers the effects of deep acceptors which slowly ionize (~103 s) to an equilibrium concentration ~5 × 1011/cm3 can explain the experimental findings on the changes of pulse shape, pulse amplitude, capacitance, energy resolution, and ?-ray efficiency with time. The operating conditions required for satisfactory stability in these detectors may be inconvenient to the user.
114 citations
TL;DR: In this article, general views on the physical aspects, mathematical image reconstruction methods and algorithms, and associated detection electronics are given; however, the technique can be applied to emission studies, for instance in positron camera.
Abstract: General views on the physical aspects, mathematical image reconstruction methods and algorithms, and associated detection electronics are given. Transmission techniques are emphasized; however, the technique can be applied to emission studies, for instance in positron camera.
83 citations
TL;DR: A work-in-progress report is presented dealing with several methods of iterative 3-dimensional reconstruction that are more accurate than the usual methods and the behavior of a number of algorithms upon varying the number of iterations.
Abstract: A work-in-progress report is presented dealing with several methods of iterative 3-dimensional reconstruction that are more accurate than the usual methods, and the behavior of a number of algorithms upon varying the number of iterations, the number of projections, the counts per projection, and the field of view of the detector.
67 citations
TL;DR: In this article, electron-hole pair creation energy for SiO 2 is shown to be ≤ 19 eV, which can be qualitatively explained in terms of columnar and/or geminate recombination.
Abstract: Charge transport studies have been performed on SiO 2 films using an electron-beam injection technique. MOS capacitors incorporating oxides grown at 1000 and 1100°C were investigated, including units fabricated at Hughes Aircraft using radiation hardening procedures. A comparison of beam-induced current vs field characteristics is made for devices with differing processing histories. Additionally, experimental determinations of trapped positive charge vs collected charge were performed. Present findings indicate that holes are mobile in SiO 2 , that the schubweg model is insufficient for describing charge transport in SiO 2 films, and that the electron-hole pair creation energy for SiO 2 is ≤ 19 eV. Current vs field data can be qualitatively explained in terms of columnar and/or geminate recombination. Conclusions concerning the effects of processing on charge buildup are made and a qualitative model based on experimental findings is presented. Implications of this model for radiation hardening are discussed.
63 citations
TL;DR: In this article, the trap mobilities, trapping times, activation energies, and trap concentration have been measured for both holes and electrons in Br and Cl-doped CdTe using the time-of-flight technique.
Abstract: The mobilities, trapping times, activation energies, and trap concentration have been measured for both holes and electrons in Br and Cl-doped CdTe using the time-of-flight technique. Two electron traps 25 and 50 meV below the conduction band and two hole traps 140 and 350 meV above the valence band have been found. The 10 times larger concentration of levels found in the Br-doped CdTe can be explained using a model that describes the association of cadmium vacancies and substitutional halogens. The physical interpretation of the ??+ product when two levels are present is discussed for this case where the mobility is reduced and the lifetime is increased by trapping-detrapping phenomena. The measurements demonstrate that the material has excellent potential for ?-ray detectors that do not polarize with the proper surface preparation and make good detectors (6 keV FWHM for 122 keV ?-ray).
61 citations
TL;DR: A new electronic cell sorter is described with emphasis on new features that insure simplicity, reliability, ease of operation, flexibility, and efficiency, and future directions of both technological development and biomedical applications are considered.
Abstract: A brief historical account of cell analysis and sorting by high-speed flow-through methods is presented The status of the Lawrence Livermore Laboratory program in this area is described, including biological applications such as the measurement of the DNA content of mouse liver cells and cultured mammalian cells Histograms of cellular DNA content can be analyzed mathematically by means of a least squares fitting code The usefulness of this procedure in extracting information on the life cycle parameters of growing cells is demonstrated A simple computer model of cell growth is used to demonstrate the accuracy of the fitting code and to elucidate shifts in the shape of the DNA histogram as a function of the fraction of cells in the DNA synthesis phase A new electronic cell sorter is described with emphasis on new features that insure simplicity, reliability, ease of operation, flexibility, and efficiency Future directions of both technological development and biomedical applications are considered
TL;DR: The electrically active impurities remaining in high-purity germanium have been identified by means of far infrared photo-conductivity measurements as mentioned in this paper, and the acceptors present in undoped crystals are boron and aluminum.
Abstract: The electrically active impurities remaining in high-purity germanium have been identified by means of far infrared photo-conductivity measurements. The principal donor is phosphorus, often accompanied by lithium and another donor which is believed to be the LiO+ complex. The acceptors present in undoped crystals are boron and aluminum. The tip ends of germanium crystals were examined by mass spectrograph, electron microprobe, and emission spectrograph analyses in a search for the possible presence of unsuspected impurities. The principal elements found were Ag in a first generation crystal and In when traces of this element had been intentionally added. Lattice defects have been studied by means of low temperature annealing and quenching experiments. Acceptor defects found in as-grown crystals can be eliminated by annealing. Two other defects which anneal in the 20-160°C range are found in quenched samples.
TL;DR: In this paper, the authors used a single dominant trap model to explain the observed transient waveforms of HgI2 detectors with alpha-particle excitation, with only partial success, due to the strongly excitonic character of the material.
Abstract: Mercuric iodide single crystals have been grown by static and dynamic sublimation methods. Characteristics of contacts and detector capacitance have been studied by photon excitation methods. Gamma and X-ray spectrometry has been carried out with completed detectors showing resolutions comparable to the best results published to date. A measurement of hole trapping length has been made from the spectral shapes observed and has been found to be approximately 0.3 mm. Transient waveform analysis with alpha-particle excitation shows hole mobilities of approximately 3 cm2/V-sec for a highly purified crystal and 0.05 for an expected less pure crystal. Electron mobilities of 120 cm2/V-sec are observed. An attempt is made to explain the observed transient waveforms in terms of a single dominant trap model, with only partial success. Due to the strongly excitonic character of the material, it is proposed that the unfamiliar observations made regarding transport properties with the HgI2 detectors studied may be due to exciton dissociation under high electric fields, to long exciton lifetimes and to interactions between excitons and trapping centers in the material.
TL;DR: In this paper, a HgI2 x-ray detector up to 16 mm3 has been made from single crystals grown from the vapor phase, and its growth, detector fabrication, and transport properties are described.
Abstract: HgI2 x-ray detectors up to 16 mm3 have been made from single crystals grown from the vapor phase. Crystal growth, detector fabrication, and transport properties are described. Resolutions of 850 eV FWHM at 5.9 keV and 4.3 keV FWHM at 122 keV have been measured at 25° C in air.
TL;DR: In this paper, the permanent and transient radiation-induced optical transmission loss in both fibers and relevant bulk glasses is investigated in both high-loss and low-loss fiber optic data transmission links.
Abstract: With the deployment of fiber optic data transmission links in military and domestic communications systems which may be subjected to various levels of ionizing radiation it is of interest to determine both the permanent and transient radiation-induced optical transmission loss in both fibers and relevant bulk glasses. Loss produced by both Co60 γ-irradiation and by pulsed electron (0.5 MeV) irradiation in both high-loss and low-loss fibers is presented. Luminescence for some hundreds of microseconds following pulsed electron irradiation of low-loss fibers is briefly discussed in terms of possible electromagnetic interference effects.
TL;DR: In this article, the effects of dopants and impurities such as Ge, Ti, Fe, Al, and OH on radiation-resistance have been determined, using pulsed and continuous radiation sources in bulk materials and in most commercially available fiber bundles.
Abstract: Irradiation of fiber optic waveguides with X-rays, gamma-rays, electrons, or neutrons can cause luminescence and losses in optical transmission. These effects have been measured, using pulsed and continuous radiation sources, in bulk materials and in most commercially available fiber bundles. Some important effects of dopants and impurities such as Ge, Ti, Fe, Al, and OH on radiation-resistance have also been determined. Transient absorption and luminescence were measured from 10 ns to 0.1s after irradiation (10 to 106 rads and 109 to 1013 rads/sec), and the permanent absorption was measured from 24 to 72 hours after irradiation (103 to 109 rads). These results show that synthetic vitreous silica (undoped), some doped silicas, polymethylmethacrylate and polystyrene can be used in radiation environments that are encountered in space and military applications. The utility of each of these fibers depends on the particular radiation environment, the length of waveguide, the wavelength of signal light, the time any system can be “off the air”, and constraints imposed by fiber cost. The data can be used to determine the response of actual fiber systems during and after irradiation.
TL;DR: In this article, two mechanisms were identified as being responsible for the radiation-induced leakage currents in n-channel SOS transistors: charge trapping in the sapphire and the consequent formation of a channel at the silicon-sapphire interface.
Abstract: High drain-leakage currents have been observed in n-channel SOS transistors after exposure to ionizing radiation. These currents could not be explained by the change in gate threshold voltage or by other radiation effects in the gate insulator. Two mechanisms were identified as being responsible for the radiation-induced leakage current. Charge trapping in the sapphire and the consequent formation of a channel at the silicon-sapphire interface is the major cause of the leakage current. Under some conditions, a smaller component of leakage current can also result from charge trapping in the silicon dioxide at island edges.
TL;DR: In this article, a fast C-V measurement technique was used to investigate the field-injected photo-depopulation properties of Si-Al 2 O 3 capacitors, and the results indicated that electron injection under positive bias and trapping of radiation-generated holes are dominated by an interface transition region at the Si-al 2 o 3 interface which need not extend further than 20-30 A from the Si substrate to account for the observations.
Abstract: Rapid annealing after radiation and field injection characteristics of Al 2 O 3 MIS capacitors have been investigated by means of a fast C-V measurement technique. The results indicate that electron injection under positive bias and trapping of radiation-generated holes are dominated by an interface transition region at the Si-Al 2 O 3 interface which need not extend further than 20–30 A from the Si substrate to account for the observations. The field injection charging characteristics are well described by a model invoking direct tunneling of electrons from the Si valence band into electron traps in the interface transition region with an energy distribution consistent with field-injected photo-depopulation studies.
TL;DR: In this paper, the role of excess vacancies, oxygen and high dislocation density in producing trapping in detectors is discussed and the important problems of material development are well delineated but that their solutions will require intensified effort.
Abstract: The present state of our knowledge of the properties of high purity germanium is reviewed. The role of excess vacancies, oxygen and high dislocation density in producing trapping in detectors is discussed. By the application of Fourier Transform Spectroscopy, the major impurities have been identified and aluminum has been found to be the dominant one in most crystals. Analysis has shown that the principal source of aluminum is the polycrystalline starting material. The material problems related to detector fabrication are surveyed and a spectrum taken with a 43 cm3 coaxial detector is presented. It is concluded that the important problems of material development are well delineated but that their solutions will require intensified effort.
TL;DR: The performance of halogen-doped CdTe gamma-ray detectors has been improved significantly by the development of new device fabrication methods as mentioned in this paper, and these detectors do not exhibit any of the previously observed polarization effects.
Abstract: Performance of halogen-doped CdTe gamma - ray detectors has been improved significantly by the development of new device fabrication methods. In particular, these detectors do not exhibit any of the previously observed polarization effects. Room temperature resolution of 7% at 122 keV has been achieved using applied fields of less than 50 V/mm for detectors up to 100 mm3 in volume.
TL;DR: In this article, a gas-proportional scintillation counters have been performed using a large alpha source, reasonable spectral resolution (< 25-k), and including the strong near-infrared transitions in noble gases excluded in all previous studies.
Abstract: New studies of gas-proportional scintillation counters have been performed using a large alpha source, reasonable spectral resolution (< 25-k), and including the strong near-infrared transitions in noble gases excluded in all previous studies. The results indicate that several new gas mixtures show promise for detectors to measure the neutron fluxes in a reactor over a wide range of values and in many nuclear physics applications where fast response and good energy resolution are desired. When used with an isotopic source the device can be used as a portable, variable-intensity light source or to detect trace amounts of atmospheric contaminants such as CO, NO, and Hg. The work also has provided useful data for laser systems pumped by ionizing radiation as well as for the operation of plasma display panels.
TL;DR: In this article, a measuring system was developed for studying and optimizing the time-resolution capabilities of fast photoelectric devices, such as standard and micro-channel type photomultipliers, which incorporated a subnanosecond light-pulse generator capable of operating at repetition frequencies up to 3 MHz with output light pulses having a full width at half-maximum of less than 200 psec.
Abstract: A measuring system has been developed for studying and optimizing the time-resolution capabilities of fast photoelectric devices, such as standard and microchannel type photomultipliers. The system incorporates a subnanosecond light-pulse generator capable of operating at repetition frequencies up to 3 MHz with output light pulses having a full width at half-maximum of less than 200 psec, and a zero-crossing discriminator which has a time walk of ±40 psec over a 170 mV to 8 V input-pulse amplitude variation. Averaging the data from several successive measurements, the measuring system time resolution is 20 psec.
TL;DR: In this paper, a prototype gamma camera system has been constructed which is based on a high purity germanium detector fabricated with orthogonal strip electrodes, where position sensitivity is obtained by connecting each contact strip on the detector to a charge-dividing resistor network.
Abstract: A prototype gamma camera system has been constructed which is based on a high purity germanium detector fabricated with orthogonal strip electrodes. In this device, position sensitivity is obtained by connecting each contact strip on the detector to a charge-dividing resistor network. Excellent energy and spatial resolution have been achieved by cooling the resistor network to 77°K and by proper selection of noise filtering parameters in the pulse shaping amplifier circuitry. The significant advantage of employing this charge-splitting detector in a semiconductor gamma camera system is its electronic-readout simplicity, requiring only three amplifier channels to measure the energy and two-dimensional location of gamma ray events. A complete discussion of our investigation of the charge-splitting detector concept is presented with special reference to its potential use in the construction of a high resolution gamma imaging system having sufficient field of view and sensitivity for clinical utilization. Several orthogonal strip-electrode germanium detectors have been fabricated and evaluated experimentally in our laboratory. The most recent of these measures 2 cm × 2 cm × 5 mm thick and incorporates 10 contact strips on each surface which are spaced on 2 mm centers. The measured FWHM energy and spatial resolutions were 5.5 keV and 1.66 mm, respectively. Theoretical calculation of the magnitude of noise in the energy channel and comparison of these values to measured data shows that correlated noise cancellation significantly enhances the energy resolution in this type of charge splitting device.
TL;DR: In this article, it is suggested that a large concentration of E′ centers is expected near the oxygen deficient Si-SiO 2 interface of irradiated MOS devices and that the presence of these defects is one source of positive space charge buildup within the first hundred Angstroms of the oxide.
Abstract: Defect center production in irradiated silica is shown to exceed that found in stoichiometric SiO 2 . The defect centers observed are the E′ type which are associated with oxygen vacancies. It is suggested that a large concentration of E′ centers is expected near the oxygen deficient Si-SiO 2 interface of irradiated MOS devices and that the presence of these defects is one source of positive space charge buildup within the first hundred Angstroms of the oxide. In addition, the 4500A emission band observed in irradiated SiO 2 has been shown to be associated with the decay of E′ centers.
TL;DR: In this article, the problem associated with transmission tomography and its implications in solving large numbers of simultaneous equations and associated parameters, such as multimillion weighting factors, are addressed.
Abstract: This paper is addressed to the problem associated with transmission tomography and its implications in solving large numbers of simultaneous equations and associated parameters, such as multimillion weighting factors Mathematical approaches to this problem in several directions are briefly reviewed and a technique (linear superposition technique with compensation) developed for this purpose, along with results obtained with this method is presented Another important aspect of the multiple scanning tomography is counting statistics which requires the count rate be in the order of 5 MHz or more for the pulse counting to have statistical accuracy of 05% or better Several alternative detectors besides conventional Sodium Iodine (NaI(Tl)) detector, namely, plastic scintillator (with enhanced photoelectric absorbtion by, for instance, tin loading) and various semiconductor detectors, such as CdTe and possible HgI2 are under investigation Plastic scintillators will naturally be a suitable candidate owing to their fast light decay characteristics A tin loaded plastic scintillator (HE 140 type) is under investigation and some of the preliminary results are reported With the semiconductor detectors, the preliminary charge collection time observations and calculations indicate that these new exotic detectors (CdTe and HgI2) can be applicable to the high rate operations primarily by virtue of their short charge collection times and moderately good energy resolutions
TL;DR: In this article, the effect of radiation induced charge trapping at the silicon sapphire interface and its effect on MIS/SOS device performance has been experimentally determined for a total ionizing dose up to 108 rads (Si).
Abstract: The radiation induced charge trapping at the silicon sapphire interface and its effect on MIS/SOS device performance has been experimentally determined for a total ionizing dose up to 108 rads (Si). These effects were determined by measuring the electrical characteristics of three types of device structures fabricated in SOS material: MIS devices with hardened and unhardened gate insulators, JFET's and diodes. The main emphasis is on the use of novel JFET structures for characterizing the SOS interface by modulating the gate depletion region against the sapphire substrate. Micrographs are also presented which show radiation induced changes in the staining characteristics of angle lapped and stained sections of the SOS interface. The experimental results indicate that positive charge is trapped in the sapphire substrate near the silicon-sapphire interface due to the total ionizing radiation. A model of the radiation induced charge trapping at the silicon sapphire interface is proposed.
TL;DR: In this article, the effects of radiation on MOS devices are reviewed, and the problems associated with radiation tolerant CMOS/SOS devices with hard gate dielectric are described.
Abstract: Radiation tolerant CMOS circuits can be made by building them in a thin film of silicon-on-sapphire (SOS) with a hard gate dielectric. Radiation effects in MOS devices are reviewed, and the problems associated with radiation tolerant CMOS/SOS devices are described. Some gate dielectric techniques which show promise in hardening CMOS circuits are presented, and the radiation behavior of Al 2 O 3 gate dielectrics are described.
TL;DR: In this paper, the elementary principles of energy dispersive X-ray fluorescence spectrometry with special reference to multielement analysis of pollutants are outlined and some results are given for analysis of air particulates, wear debris in oils and suspended and dissolved solids in fresh water.
Abstract: This paper outlines the elementary principles of energy dispersive X-ray fluorescence spectrometry with special reference to multielement analysis of pollutants. Typical equipment, using radioisotope sources for X-ray excitation, is described and some results are given for analysis of air particulates, wear debris in oils and suspended and dissolved solids in fresh water. The use of "thin" specimens is discussed for reducing interelement and particle size effects, increasing sensitivity and simplifying preparation of standards and samples.
TL;DR: Results obtained with a 1-cm2, 4 mm deep, 5×5 strip high purity germanium detector are 2.1 mm full width spatial resolution, a measured single strip resolution of 0.65 mmFull width half maximum (FWHM), and a 25 element uncollimated energy resolution of 2.95 keV FWHM.
Abstract: High purity germanium offers excellent potential for use in nuclear medical imaging cameras. A position and energy readout technique using two inexpensive delay lines has been developed for these cameras. Results obtained with a 1-cm2 , 4 mm deep, 5×5 strip high purity germanium detector are 2.1 mm full width spatial resolution, a measured single strip resolution of 0.65 mm full width half maximum (FWHM), a 25 element uncollimated energy resolution of 2.95 keV FWHM, and 2.65 keV FWHM for a single central element at 140 keV.
TL;DR: In this article, semi-insulating CdTe was grown from indium-doped tellurium-rich solutions with resolutions as low as 6% (FWHM) for 137Cs.
Abstract: Semi-insulating CdTe was grown from indium-doped tellurium-rich solutions. Ten 1/2-cm3 devices were fabricated with resolutions as low as 6% (FWHM) for 137Cs. Polarization phenomena were not observed for tests performed from -36 to 65°C. Full energy peak counting efficiencies were less than theoretically predicted because of trapping. In addition, resolutions as low as 3 keV for 241Am were obtained with smaller (?15 mm3) devices.