813 research outputs found
Radiographic testing at Lawrence Livermore National Laboratory
No full textRadiographic testing is a nondestructive inspection technique which uses penetrating radiation. The Nondestructive Evaluation (NDE) Section at Lawrence Livermore National Laboratory has a broad spectrum of equipment and techniques for radiographic testing. These resources include low-energy vacuum systems, low- and mid-energy cabinet and cell radiographic systems, high-energy linear accelerators, portable x-ray machines and radioisotopes for radiographic inspections. For diagnostic testing the NDE Section also has real-time and flash radiographic equipment
Distorted electron acceptors: an unexpected reaction involving tetramethyl-TCNQ
No full textReactions involving the donors N-methyl-2-methylbenzothiazolium-and N-(1-propyl)-2-methylbenzothiazolium iodide with the acceptor 2,3,5,6-tetramethyl-7,7,8,8-tetracyano-p-quinodimethane (TMTCNQ) in the presence of a suitable base lead to the isolation of novel [(Z)-beta-(N-alkylbenzothiazol-3-ium-2-yl)-alpha-cyano-2,3,5,6-tetrameth yl-4-styryl]dicyanomethanide chromophores. Under prolonged reaction periods, these first examples of charge transfer compounds incorporating the distorted TMTCNQ electron acceptor, undergo further reaction at the acrylonitrile functionality promoting the synthesis of novel thiomorpholine-based charge transfer compounds via a sulfur mediated cyclisation reaction. This second reaction illustrates a fundamentally new type of TCNQ-based chemistry as confirmed by X-ray crystallography and high-resolution mass spectrometry. A possible reaction mechanism for the formation of the thiomorpholine-based chromophores is considered
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High intensity positron program at LLNL
No full textLawrence Livermore National Laboratory (LLNL) is the home of the world's highest current beam of keV positrons. The potential for establishing a national center for materials analysis using positron annihilation techniques around this capability is being actively pursued. The high LLNL beam current will enable investigations in several new areas. We are developing a positron microprobe that will produce a pulsed, focused positron beam for 3-dimensional scans of defect size and concentration with submicron resolution. Below we summarize the important design features of this microprobe. Several experimental end stations will be available that can utilize the high current beam with a time distribution determined by the electron linac pulse structure, quasi-continuous, or bunched at 20 MHz, and can operate in an electrostatic or (and) magnetostatic environment. Some of the planned early experiments are: two-dimensional angular correlation of annihilation radiation of thin films and buried interfaces, positron diffraction holography, positron induced desorption, and positron induced Auger spectra
An estimate of collisional beam scattering during final focus in NDCX-II
No full textThe final focus of NDCX-II contains a region with quite high plasma density. We estimate here how much collisional scatter we expect from transit through this plasma. A separate question, not explored here, is how much scatter there might be off of collective fluctuations in the neutralizing plasma, including those driven by the passage of the beam
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Radiation damage of germanium detectors
No full textIn the course of a continuing study of the proton damage of germanium detectors, a reverse electrode configuration coaxial detector that had been fabricated at Lawrence Berkeley Laboratory (LBL) five years ago and a 1 cm thick planar detector made from the same crystal were irradiated with 5.1 GeV protons in a recent experiment. These detectors were irradiated simultaneously--there were actually a total of five detectors in line. The coaxial detector was considerably less sensitive to the high-energy proton damage than was the planar detector. These data indicate a factor of approx. 3. This would imply a factor of approx. 60 when comparing coaxial detectors having the opposite electrode configuration. Although additional experiments must be done, the evidence is now quite strong that coaxial germanium detectors having the n/sup +/ contact on the coaxial periphery should not be used in any situation subject to significant radiation damage such as on an extended mission in space
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Low-energy, high-intensity positron beam experiments with a linac
No full textPrevious experiments with positrons from radionuclides have demonstrated that positron beams are a rich source of information about the surface condition of solids. We have now demonstrated the possibility of producing very intense beams at the Lawrence Livermore 100 MeV electron linac and installed an apparatus that produces a variable energy positron beam at energies between 500 eV and 20 keV with sufficient intensity to perform a variety of new positron experiments. The positron beam is pulsed with 10 ns to 3 microseconds duration at rates up to 1440 pulses per second, with as many as 10/sup 6/ positrons available per pulse. Experiments that require either pulsed or steady currents are possible in an ultrahigh vacuum environment. For the first time two-dimensional angular correlation spectra of the surface positron and positronium annihilation at a single crystal sample have been obtained for copper. 6 references, 4 figures, 1 table
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High-energy proton radiation damage of high-purity germanium detectors
No full textMotivated by their applicability to gamma-ray spectroscopy experiments in space, quantitative studies of radiation damage effects in high-purity germanium detectors due to high-energy charged particles have been initiated with the irradiation by 6 GeV/c protons of two 1.0 cm thick planar detectors maintained at 88/sup 0/K. The threshold for resolution degradation and the annealing characteristics differs markedly from those previously observed for detectors irradiated by fast neutrons. Under proton bombardment, degradation in the energy resolution was found to begin below 7 x 10/sup 7/ protons/cm/sup 2/, and increased proportionately in both detectors until the experiment was terminated at a total flux of 5.7 x 10/sup 8/ protons/cm/sup 2/, equivalent to about a six year exposure to cosmic-ray protons in space. At the end of the irradiation, the FWHM resolution measured at 1332 keV stood at 8.5 and 13.6 keV, with both detectors of only marginal utility as a spectrometer due to the severe tailing caused by charge trapping. The two detectors displayed a significant difference in proton damage sensitivity, which is consistent with fast neutron damage effects. To ensure that detector variability did not influence the comparison of proton- and neutron-induced damage effects, one of the detectors had been used previously in a neutron damage experiment. The threshold for high-energy proton damage was found to be markedly lower, roughly 5 x 10/sup 7/ protons/cm/sup 2/, compared to 3 x 10/sup 9/ neutrons/cm/sup 2/ for fast neutrons. Annealing these detectors after proton damage was found to be much easier than after neutron damage. A satisfactory level of recovery after high-energy proton damage can be achieved with in-situ annealing in the range of 100/sup 0/C
Radiological impact of high-energy accelerators on the environment
No full textThe potential radiological impact of high-energy, high-intensity accelerators in the environment is discussed. It is shown that there are three sources of radiation exposure to the general public resulting from the operation of high-energy accelerators. In order of importance these are (a) the prompt radiation field, produced when the accelerator is operating; (b) the release of radionuclides and aerosols into the atmosphere; and (c) the production of radionuclides in the groundwater system around the accelerator. Of these three sources, (a) is dominant and typically exceeds (b) by about an order of magnitude. To date, experience at many accelerator laboratories has shown that the quantity of accelerator-produced radionuclides released to nearby groundwater systems (c) is either extremely small or immeasurable. The population dose equivalent resulting from the operation of several large high-energy facilities is compared
Optimal Placement and Sizing of Distributed Generation
No full textIn this thesis work we solve the problem of optimal placement and sizing of distributed generation by using an original Fuzzy Adaptive Particle Swarm Optimization algorithm and a Mixed Integer Linear Programming formulation of the problem. The goal of integrating Fuzzy Logic in Particle Swarm Optimization is to be able to overcome some of the classical disadvantages of the algorithm. Particle Swarm Optimization has been traditionally criticized for the complexity to set the acceleration constants of the algorithm and the low exploration capabilities of the algorithm. In this thesis work, it is proposed a new implementation of Particle Swarm Optimization that avoids the complex setting procedure of the acceleration constants of the algorithm, while aiming at improving the exploration capabilities of the algorithm. In this thesis work it is also analyzed a novel Mixed Integer Linear Programming formulation of the problem of optimal sitting of distributed generation in distribution networks implemented in DER- CAM, a tool developed at the Lawrence Berkeley National Laboratory. The results of the two models are analyzed and contrasted against each other for a real case study of an islanded microgrid located in the north of the U.S. Results obtained in the case study depict the differences between the two analyzed approaches to solve the problem. It is found that over and under estimations of voltage magnitudes in high and low loading scenarios of distribution networks have the potential to impact investment decisions in distributed generation capacity for the linear formulation of the problem. Also the models analyzed depict the synergies between renewable energy technologies and thermal generators to increase energy savings while maintaining the operation limits of the grid.Technology, Policy and ManagementEngineering and Policy AnalysisEngineering and Policy Analysi
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Detectors for high resolution dynamic pet
No full textThis report reviews the motivation for high spatial resolution in dynamic positron emission tomography of the head and the technical problems in realizing this objective. We present recent progress in using small silicon photodiodes to measure the energy deposited by 511 keV photons in small BGO crystals with an energy resolution of 9.4% full-width at half-maximum. In conjunction with a suitable phototube coupled to a group of crystals, the photodiode signal to noise ratio is sufficient for the identification of individual crystals both for conventional and time-of-flight positron tomography
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