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Search Results: 1 - 10 of 175556 matches for " Steven E. Boggs "
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Simulated Performance of a Germanium Compton Telescope
Steven E. Boggs,Pierre Jean
Physics , 2000,
Abstract: To build upon the goals of the upcoming INTEGRAL mission, the next generation soft gamma-ray (0.2-20 MeV) observatory will require improved sensitivity to nuclear line emission while maintaining high spectral resolution. We present the simulated performance of a germanium Compton telescope (GCT) design, which will allow a factor of ten improvement in sensitivity over INTEGRAL/SPI. We also discuss a number of issues concerning reconstruction techniques and event cuts, and demonstrate how these affect the overall performance of the telescope.
Supracervical Lymph Node Biopsy under Local Anesthesia: A Cautionary Tale!  [PDF]
Steven D. Boggs, Elizabeth A. M. Frost
Open Journal of Anesthesiology (OJAnes) , 2015, DOI: 10.4236/ojanes.2015.53009
Abstract: A middle aged woman was scheduled for supracervical lymph node biopsy under local anesthesia. A scheduling conflict caused a significant operating room delay and she became very nervous. A surgical resident asked for anesthetic assistance in calming the patient. Assured that the case was under local anesthesia only, the anesthesiologist gave the patient soda to drink. In the operating room, the lady could not tolerate the procedure but as she now was at risk for aspiration, the anesthesiologist suggested the case be terminated and rescheduled. The surgeon disagreed and continued but was confronted with substantial bleeding. Emergency induction of general anesthesia was required. Postoperatively bleeding continued requiring re-exploration and intensive care unit admission. The patient developed a compressive left brachial plexopathy. The anatomy of the area indicated that general anesthesia was the preferred technique. The importance of team work and communication is underscored. Complications are more frequent when perioperative changes are made.
Unveiling Physical Processes in Type Ia Supernovae With a Laue Lens Telescope
Nicolas M. Barrière,John A Tomsick,Steven E. Boggs,Peter von Ballmoos,Julien Rousselle
Physics , 2011,
Abstract: We present in this paper a focusing gamma-ray telescope that has only one goal: addressing the true nature of Type Ia Supernovae (SNe Ia). This telescope is based on a Laue lens focusing a 100-keV wide energy band centered on 847 keV, which correspond to a bright line emitted by the decay chain of 56Ni, a radioactive element massively produced during SNe Ia events. Spectroscopy and light curve measurements of this gamma-ray line allow direct measurement of the underlying explosion physics and dynamics, and thus discriminate among the competing models. However reaching this goal the observation of several events with high detection significance, meaning more powerful telescopes. The telescope concept we present in this paper is composed of a Laue lens held 30 m apart from the focal instrument (a compact Compton telescope) by an extensible mast. With a 3-sigma sensitivity of 1.8\times10-6 ph/s/cm2 in the 3%-broadened line at 847 keV (in 1Ms observation time), dozens of SNe Ia could be detected per year out to \sim40 Mpc, enough to perform detailed time-evolved spectroscopy on several events each year. This study took place in the framework of the DUAL mission proposal which was recently submitted to ESA for the third medium class mission of the Cosmic Vision program.
Developing a second generation Laue lens prototype: high reflectivity crystals and accurate assembly
Nicolas M. Barrière,John A. Tomsick,Steven E. Boggs,Alexander Lowell,Peter von Ballmoos
Physics , 2011, DOI: 10.1117/12.899893
Abstract: Laue lenses are an emerging technology that will enhance gamma-ray telescope sensitivity by one to two orders of magnitude in selected energy bands of the \sim 100 keV to \sim 1.5 MeV range. This optic would be particularly well adapted to the observation of faint gamma ray lines, as required for the study of Supernovae and Galactic positron annihilation. It could also prove very useful for the study of hard X-ray tails from a variety of compact objects, especially making a difference by providing sufficient sensitivity for polarization to be measured by the focal plane detector. Our group has been addressing the two key issues relevant to improve performance with respect to the first generation of Laue lens prototypes: obtaining large numbers of efficient crystals and developing a method to fix them with accurate orientation and dense packing factor onto a substrate. We present preliminary results of an on-going study aiming to enable a large number of crystals suitable for diffraction at energies above 500 keV. In addition, we show the first results of the Laue lens prototype assembled using our beamline at SSL/UC Berkeley, which demonstrates our ability to orient and glue crystals with accuracy of a few arcsec, as required for an efficient Laue lens telescope.
Properties of Pt Schottky Type Contacts On High-Resistivity CdZnTe Detectors
Aleksey E. Bolotnikov,Steven E. Boggs,C. M. Hubert Chen,Walter R. Cook,Fiona A. Harrison,Stephen M. Schindler
Physics , 2001, DOI: 10.1016/S0168-9002(01)01506-6
Abstract: In this paper we present studies of the I-V characteristics of CdZnTe detectors with Pt contacts fabricated from high-resistivity single crystals grown by the high-pressure Brigman process. We have analyzed the experimental I-V curves using a model that approximates the CZT detector as a system consisting of a reversed Schottky contact in series with the bulk resistance. Least square fits to the experimental data yield 0.78-0.79 eV for the Pt-CZT Schottky barrier height, and <20 V for the voltage required to deplete a 2 mm thick CZT detector. We demonstrate that at high bias the thermionic current over the Schottky barrier, the height of which is reduced due to an interfacial layer between the contact and CZT material, controls the leakage current of the detectors. In many cases the dark current is not determined by the resistivity of the bulk material, but rather the properties of the contacts; namely by the interfacial layer between the contact and CZT material.
In-flight PSF calibration of the NuSTAR hard X-ray optics
Hongjun An,Kristin K. Madsen,Niels J. Westergaard,Steven E. Boggs,Finn E. Christensen,William W. Craig,Charles J. Hailey,Fiona A. Harrison,Daniel K. Stern,William W. Zhang
Physics , 2014, DOI: 10.1117/12.2055481
Abstract: We present results of the point spread function (PSF) calibration of the hard X-ray optics of the Nuclear Spectroscopic Telescope Array (NuSTAR). Immediately post-launch, NuSTAR has observed bright point sources such as Cyg X-1, Vela X-1, and Her X-1 for the PSF calibration. We use the point source observations taken at several off-axis angles together with a ray-trace model to characterize the in-orbit angular response, and find that the ray-trace model alone does not fit the observed event distributions and applying empirical corrections to the ray-trace model improves the fit significantly. We describe the corrections applied to the ray-trace model and show that the uncertainties in the enclosed energy fraction (EEF) of the new PSF model is < 3% for extraction apertures of R > 60" with no significant energy dependence. We also show that the PSF of the NuSTAR optics has been stable over a period of ~300 days during its in-orbit operation.
Developing a method for soft gamma-ray Laue lens assembly and calibration
Nicolas M. Barrière,John A. Tomsick,Steven E. Boggs,Alexander Lowell,Colin Wade,Max Baugh,Peter von Ballmoos,Nikolay V. Abrosimov,Lorraine Hanlon
Physics , 2013, DOI: 10.1016/j.nima.2013.12.006
Abstract: Laue lenses constitute a promising option for concentrating soft gamma rays with a large collection area and reasonable focal lengths. In astronomy they could lead to increased telescope sensitivity by one to two orders of magnitude, in particular for faint nuclear gamma-ray lines, but also for continua like hard X-ray tails from a variety of compact objects. Other fields like Homeland security and nuclear medicine share the same need for more sensitive gamma-ray detection systems and could find applications for gamma-ray focusing optics. There are two primary challenges for developing Laue lenses: the search for high-reflectivity and reproducible crystals, and the development of a method to accurately orient and fix the thousands of crystals constituting a lens. In this paper we focus on the second topic. We used our dedicated X-ray beamline and Laue lens assembly station to build a breadboard lens made of 15 crystals. This allowed us to test our tools and methods, as well as our simulation code and calibration procedure. Although some critical points were identified, the results are very encouraging, with a crystal orientation distribution lower than $10''$, as required to build a Laue lens telescope dedicated to the study of Type Ia supernovae (30-m focal length). This breadboard lens represents an important step towards raising the technology readiness level of Laue lenses.
XMM-Newton Finds That SAX J1750.8-2900 May Harbor the Hottest, Most Luminous Known Neutron Star
Alexander W. Lowell,John A. Tomsick,Craig O. Heinke,Arash Bodaghee,Steven E. Boggs,Philip Kaaret,Sylvain Chaty,Jerome Rodriguez,Roland Walter
Physics , 2012, DOI: 10.1088/0004-637X/749/2/111
Abstract: We have performed the first sensitive X-ray observation of the low-mass X-ray binary SAX J1750.8-2900 in quiescence with XMM-Newton. The spectrum was fit to both a classical black body model, and a non-magnetized, pure hydrogen neutron star atmosphere model. A power law component was added to these models, but we found that it was not required by the fits. The distance to SAX J1750.8-2900 is known to be D = 6.79 kpc from a previous analysis of photospheric radius expansion bursts. This distance implies a bolometric luminosity (as given by the NS atmosphere model) of (1.05 +/- 0.12) x 10^34 (D/6.79 kpc)^2 erg s^-1, which is the highest known luminosity for a NS LMXB in quiescence. One simple explanation for this surprising result could be that the crust and core of the NS were not in thermal equilibrium during the observation. We argue that this was likely not the case, and that the core temperature of the NS in SAX J1750.8-2900 is unusually high.
High Energy X-Ray Detection OF G359.89-0.08 (Sgr A-E): Magnetic Flux Tube Emission Powered By Cosmic Rays?
Shuo Zhang,Charles J. Hailey,Frederick K. Baganoff,Franz E. Bauer,Steven E. Boggs,William W. Craig,Finn E. Christensen,Eric V. Gotthelf,Fiona A. Harrison,Kaya Mori,Melania Nynka,Daniel Stern,John A. Tomsick,William W. Zhang
Physics , 2014, DOI: 10.1088/0004-637X/784/1/6
Abstract: We report the first detection of high-energy X-ray (E>10 keV) emission from the Galactic Center non-thermal filament G359.89-0.08 (Sgr A-E) using data acquired with the Nuclear Spectroscopic Telescope Array (NuSTAR). The bright filament was detected up to ~50 keV during a NuSTAR Galactic Center monitoring campaign. The featureless power-law spectrum with a photon index of ~2.3 confirms a non-thermal emission mechanism. The observed flux in the 3-79 keV band is ~ 2.0e-12 erg/cm^2/s, corresponding to an unabsorbed X-ray luminosity of ~2.6e34 erg/s assuming a distance of 8.0 kpc. Based on theoretical predictions and observations, we conclude that Sgr A-E is unlikely to be a pulsar wind nebula (PWN) or supernova remnant-molecular cloud (SNR-MC) interaction, as previously hypothesized. Instead, the emission could be due to a magnetic flux tube which traps TeV electrons. We propose two possible TeV electron sources: old PWNe (up to ~100 kyr) with low surface brightness and radii up to ~30 pc or molecular clouds (MCs) illuminated by cosmic rays (CRs) from CR accelerators such as SNRs or Sgr A*.
Initial Results from NuSTAR Observations of the Norma Arm
Arash Bodaghee,John A. Tomsick,Roman Krivonos,Daniel Stern,Franz E. Bauer,Nicolas Barriere,Steven E. Boggs,Finn E. Christensen,William W. Craig,Eric V. Gotthelf,Charles J. Hailey,Fiona A. Harrison,Jaesub Hong,Kaya Mori,William W. Zhang
Physics , 2014, DOI: 10.1088/0004-637X/791/1/68
Abstract: Results are presented for an initial survey of the Norma Arm gathered with the focusing hard X-ray telescope NuSTAR. The survey covers 0.2 deg$^2$ of sky area in the 3-79 keV range with a minimum and maximum raw depth of 15 ks and 135 ks, respectively. Besides a bright black-hole X-ray binary in outburst (4U 1630-47) and a new X-ray transient (NuSTAR J163433-473841), NuSTAR locates three sources from the Chandra survey of this region whose spectra are extended above 10 keV for the first time: CXOU J163329.5-473332, CXOU J163350.9-474638, and CXOU J163355.1-473804. Imaging, timing, and spectral data from a broad X-ray range (0.3-79 keV) are analyzed and interpreted with the aim of classifying these objects. CXOU J163329.5-473332 is either a cataclysmic variable or a faint low-mass X-ray binary. CXOU J163350.9-474638 varies in intensity on year-long timescales, and with no multi-wavelength counterpart, it could be a distant X-ray binary or possibly a magnetar. CXOU J163355.1-473804 features a helium-like iron line at 6.7 keV and is classified as a nearby cataclysmic variable. Additional surveys are planned for the Norma Arm and Galactic Center, and those NuSTAR observations will benefit from the lessons learned during this pilot study.
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