A novel method for modeling the neutron Time of Flight (nTOF) detector response in current mode to inertial confinement fusion experiments

There are several machines in this country that produce short bursts of neutrons for various applications. A few examples are the Z-machine, operated by Sandia National Laboratories in Albuquerque, NM; the OMEGA Laser Facility at the University of Rochester in Rochester, NY; and the National Ignition Facility (NIF) operated by the Department of Energy at Lawrence Livermore National Laboratory in Livermore, California. They all incorporate neutron time of flight (nTOF) detectors which measure neutron yield, and the shapes of the waveforms from these detectors contain germane information about the plasma conditions that produce the neutrons. However, the signals can also be clouded\u27 by a certain fraction of neutrons that scatter off structural components and also arrive at the detectors, thereby making analysis of the plasma conditions more difficult. These detectors operate in current mode — i.e., they have no discrimination, and all the photomultiplier anode charges are integrated rather than counted individually as they are in single event counting. Up to now, there has not been a method for modeling an nTOF detector operating in current mode. MCNP-PoliMi** was developed in 2002 to simulate neutron and gamma-ray detection in a plastic scintillator, which produces a collision data output table about each neutron and photon interaction occurring within the scintillator; however, the post-processing code which accompanies MCNP-PoliMi assumes a detector operating in single-event counting mode and not current mode. Therefore, the idea for this work had been born: could a new post-processing code be written to simulate an nTOF detector operating in current mode? And if so, could this process be used to address such issues as the impact of neutron scattering on the primary signal? Also, could it possibly even identify sources of scattering (i.e., structural materials) that could be removed or modified to produce \u27cleaner\u27 neutron signals? This process was first developed and then applied to the axial neutron time of flight detectors at the Z-Facility mentioned above. First, MCNP-PoliMi was used to model relevant portions of the facility between the source and the detector locations. To obtain useful statistics, variance reduction was utilized. Then, the resulting collision output table produced by MCNP-PoliMi was further analyzed by a MATLAB post-processing code. This converted the energy deposited by neutron and photon interactions in the plastic scintillator (i.e., nTOF detector) into light output, in units of MeVee\u0444 (electron equivalent) vs time. The time response of the detector was then folded into the signal via another MATLAB code. The simulated response was then compared with experimental data and shown to be in good agreement. To address the issue of neutron scattering, an \u27Ideal Case,\u27 (i.e., a plastic scintillator) was placed at the same distance from the source for each detector location with no structural components in the problem. This was done to produce as \u27pure\u27 a neutron signal as possible. The simulated waveform from this \u27Ideal Case\u27 was then compared with the simulated data from the \u27Full Scale\u27 geometry (i.e., the detector at the same location, but with all the structural materials now included). The \u27Ideal Case\u27 was subtracted from the \u27Full Scale\u27 geometry case, and this was determined to be the contribution due to scattering. The time response was deconvolved out of the empirical data, and the contribution due to scattering was then subtracted out of it. A transformation was then made from dN/dt to dN/dE to obtain neutron spectra at two different detector locations. Matzen, K., Phys. Plasmas 4, 1519 (1997). T.R. Boehly, D.L. Brown, R.S. Craxton, R.L. Keck, J.P. Knauer, J.H. Kelly, T.J. Kessler, S.A. Kumpan, S.J. Loucks, S.A. Letzring, F.J. Marshall, R.L. McCrory, S.F.B. Mose, W. Seka, J.M. Soures, and C.P. Verdon, \u27Initial performance results of the OMEGA laser system,\u27 Opt. Commun., vol. 133, pp. 495-506, 1997. E.I. Moses, \u27The National Ignition Facility: Status and plans for the experimental program,\u27 Fusion Sci. Technol., vol 44, pp. 11-18, 2003. **S.A. Pozzi, E. Padovani, M. Marsequerra, Nucl. Instr. and Meth. A 513 (2003) 550-558. MeVee = amount of light produced by 1 MeV deposited by a Compton scattered electron

Sarbanes-Oxley Act of 2002: Are Multi-National Corporations Unduly Burdened?

The Sarbanes-Oxley Act was enacted by Congress in response to the frauds perpetrated by several large U.S. companies; Enron and WorldCom were the main catalysts for the swift regulatory response. Though the primary impetus of Sarbanes-Oxley was to deter corruption domestically, its impact has had multinational reach. Problems arise when foreign corporations domiciled outside the United States are subject to both U.S. securities law and the laws of their home country, particularly when the laws are in conflict. This five part comment examines the effect that the Sarbanes–Oxley Act of 2002 has had on multinational corporations. The comment begins by providing the background of the Act noting the circumstances that brought about its enactment. Part two outlines the sections of the Act that have a direct regulatory impact on multinational corporations registered on a United States exchange and the necessary steps that the effected corporations have taken in order to manage the regulations imposed by the Act. Some sections of the Act regulate multinational corporations specifically, while other sections indirectly affect multinational corporations. Part three of the comment analyzes the interaction of Sarbanes-Oxley with international corporate governance rules and regulations, giving particular attention to the European Union, specifically France and Germany. It examines which regulations have been more successful and the reasons for that success. The comment finds the best place to view the success of Sarbanes-Oxley is the decision of a multinational corporation to cross-list on a United States exchange. The success of the Act can also be seen by looking at the effect Sarbanes-Oxley has had on other countries’ corporate governance regulations. In part four, the comment looks at the extraterritorial applicability of United States law and how it affects the enforcement of the regulations mandated by the Sarbanes-Oxley Act on multinational corporations. It examines the history of extraterritorial power of federal legislation on activities occurring outside the United States, but having an impact domestically. The comment concludes by looking at what the Sarbanes-Oxley Act will mean for the future of corporate activity both inside and outside of the United States. It also emphasizes that legislation alone will not be enough to deter corruption, but until all corporations can effectively police themselves, there will always be the taint of corruption looming on the horizon

Theory for Calcium-Phosphate Crystal Formation in Tissue from Scanning Electron Microscope Data

Scanning electron microscope (SEM) morphological analysis combined with energy dispersive characteristic x-ray analysis provides insight into the mechanism of biological mineralization. A time series of tissue micrographs and mineralization measurements can permit the determination of the mineralization kinetic behavior and is the basis upon which a computer model has been devised. The computer model is constructed from fundamental principles of crystal nucleation and precipitation theory. Various general forms of the model are tested against the laboratory data for goodness-of-fit using the least squares method, and two models are found to be acceptable. Both of the acceptable models involve inhibition of the mineralization process which has a reaction order ranging from one to two. A third model involving constant nucleation rate must be rejected. Having established working first principle models for the mineralization process, one can compute a constant number of nucleation sites and a supersaturation value for calcium in various mineralized tissues such as the spongiosa and fibrosa of heart valve leaflet implants. These quantities are determined and used in discussing a general theory for biomineralization which emphasizes therapeutic considerations

Study of Rat Lung Alveoli using Corrosion Casting and Freeze Fracture Methods Coupled with Digital Image Analysis

Relative areas and volumes can be estimated from vascular corrosion casts of rat lung alveoli using a calibration obtained from bulk frozen hydrated tissue. These morphometric measurements are roughly independent of the shrinkage and distortion artifacts known to arise in the corrosion casting procedure. Digital image processing of the SEM micrographs is employed to facilitate the measurement of casts and frozen tissue. The vascular corrosion casting technique is modified also to permit successful casting of alveolar air passages. The modified technique produces faithful casts of dead-ended luminal structures where continuous perfusion of casting medium into the tissue is not possible. The casts of alveolar air passages and their corresponding vasculature are compared to determine the volume of a single alveolus. By utilizing the calibrated measurements of lung areas and volumes, an estimate of lung vascular surface area per unit volume is obtained. This number, when multiplied by the respiratory tidal volume of the rat, may represent the total lung vascular surface area available for physiological gas exchange during normal respiration