SONTRAC: an imaging spectrometer for solar neutrons

An instrument capable of unambiguously determining the energy and direction of incident neutrons has important applications in solar physics-as well as environmental monitoring and medical/radiological sciences. The SONTRAC (SOlar Neutron TRACking) instrument is designed to operate in the neutron energy range of 20-250 MeV. The measurement principle is based on non-relativistic double scatter of neutrons off ambient protons (n-p scattering) within a block of densely packed scintillating fibers. Using this double-scatter mode it is possible to uniquely determine neutron energy and direction on an event-by-event basis. A fully operational science model of such an instrument has been built using 300 μm (250 μm active) scintillating fibers. The science model consists of a 5×5×5 cm cube of orthogonal plastic scintillating fiber layers. Two orthogonal imaging chains, employing image intensifiers and CCD cameras, allow full 3-dimensional reconstruction of scattered proton particle tracks. We report the results of the science model instrument calibration using 35-65 MeV protons. The proton calibration is the first step toward understanding the instrument response to n-p scatter events. Preliminary results give proton energy resolution of 2% (6%) at 67.5 (35) MeV, and angular resolution of 2° (4.5°) at 67.5 (35) MeV. These measurements are being used to validate detailed instrument simulations that will be used to optimize the instrument design and develop quantitative estimates of science return. Based on the proton calibration, neutron energy and angular resolution for a 10×10×10 cm version of SONTRAC is expected to be ~5% an

Advanced characterization and simulation of SONNE: a fast neutron spectrometer for Solar Probe Plus

SONNE, the SOlar NeutroN Experiment proposed for Solar Probe Plus, is designed to measure solar neutrons from 1-20 MeV and solar gammas from 0.5-10 MeV. SONNE is a double scatter instrument that employs imaging to maximize its signal-to-noise ratio by rejecting neutral particles from non-solar directions. Under the assumption of quiescent or episodic small-flare activity, one can constrain the energy content and power dissipation by fast ions in the low corona. Although the spectrum of protons and ions produced by nanoflaring activity is unknown, we estimate the signal in neutrons and γ−rays that would be present within thirty solar radii, constrained by earlier measurements at 1 AU. Laboratory results and simulations will be presented illustrating the instrument sensitivity and resolving power

Development of the fast neutron imaging telescope

We report on the development of a next generation neutron telescope, with imaging and energy measurement capabilities, sensitive to neutrons in the 2-20 MeV energy range. The Fast Neutron Imaging Telescope (FNIT) was initially conceived to study solar neutrons as a candidate instrument for the Inner Heliosphere Sentinels (IHS) program under formulation at NASA. This detector is now being adapted to locate Special Nuclear Material (SNM) for homeland security purposes by detecting fission neutrons and reconstructing the image of their source. In either case, the detection principle is based on multiple elastic neutron-proton scatterings in organic scintillator. By reconstructing the scattering coordinates and measuring the recoil proton energy, the direction and energy of each neutron can be determined and discrete neutron sources identified. We describe the performance of the FNIT prototype, report on the current status of R&D efforts and present the results of recent laboratory measurements

Development and performance of the Fast Neutron Imaging Telescope for SNM detection

FNIT (the Fast Neutron Imaging Telescope), a detector with both imaging and energy measurement capabilities, sensitive to neutrons in the range 0.8-20 MeV, was initially conceived to study solar neutrons as a candidate design for the Inner Heliosphere Sentinel (IHS) spacecraft of NASA\u27s Solar Sentinels program and successively reconfigured to locate fission neutron sources. By accurately identifying the position of the source with imaging techniques and reconstructing the Watt spectrum of fission neutrons, FNIT can detect samples of special nuclear material (SNM), including heavily shielded and masked ones. The detection principle is based on multiple elastic neutron-proton scatterings in organic scintillators. By reconstructing n-p event locations and sequence and measuring the recoil proton energies, the direction and energy spectrum of the primary neutron flux can be determined and neutron sources identified. We describe the design of the FNIT prototype and present its energy reconstruction and imaging performance, assessed by exposing FNIT to a neutron beam and to a Pu fission neutron source

Design optimization and performance capabilities of the fast neutron imaging telescope (FNIT)

We describe the design optimization process and performance characterization of a next generation neutron telescope, with imaging and energy measurement capabilities, sensitive to neutrons in the 1-20 MeV energy range. The response of the Fast Neutron Imaging Telescope (FNIT), its efficiency in neutron detection, energy resolution and imaging capabilities were characterized through a combination of lab tests and Monte Carlo simulations. Monte Carlo simulations, together with experimental data, are also being used in the development and testing of the image reconstruction algorithm. FNIT was initially conceived to study solar neutrons as a candidate instrument for the Inner Heliosphere Sentinel (IHS) spacecraft. However, the design of this detector was eventually adapted to locate Special Nuclear Material (SNM) sources for homeland security purposes, by detecting fission neutrons. In either case, the detection principle is based on multiple elastic neutron-proton scatterings in organic scintillator. By reconstructing event locations and measuring the recoil proton energies, the direction and energy spectrum of the primary neutron flux can be determined and neutron sources identified. This paper presents the most recent results arising from our efforts and outlines the performance of the FNIT detector

Atmospheric neutron measurements with the SONTRAC science model

–The SOlar Neutron TRACking (SONTRAC) telescope was originally developed to measure the energy spectrum and incident direction of neutrons produced in solar flares, in the energy range 20 - 250 MeV. While developed primarily for solar physics, the SONTRAC detector may be employed in virtually any application requiring both energy measurement and imaging capabilities. The SONTRAC Science Model (SM) is presently being operated at the University of New Hampshire (UNH) as a ground-based instrument to investigate the energy spectrum, zenith and azimuth angle dependence of the cosmic-ray induced sea-level atmospheric neutron flux. SONTRAC measurements are based on the non-relativistic double scatter of neutrons off ambient protons within a block of scintillating fibers. Using the n-p elastic double-scatter technique, it is possible to uniquely determine the neutron’s energy and direction on an event-by-event basis. The 3D SM consists of a cube of orthogonal plastic scintillating fiber layers with 5 cm sides, read out by two CCD cameras. Two orthogonal imaging chains allow full 3D reconstruction of scattered proton tracks

Galactomannan Does Not Precede Major Signs on a Pulmonary Computerized Tomographic Scan Suggestive of Invasive Aspergillosis in Patients with Hematological Malignancies

Background. Detection of serum galactomannan (GM) antigen and presence of the halo sign on a pulmonary computerized tomographic (CT) scan have a high specificity but a low sensitivity to diagnose invasive aspergillosis (IA) in patients at risk for this disease. To our knowledge, the relationship between the time at which pulmonary infiltrates are detected by CT and the time at which GM antigens are detected by enzyme immunoassay (EIA) has not been studied. Methods. In a prospective study, tests for detection of GM were performed twice weekly for patients with hematological malignancies who had undergone hematopoetic stem cell transplantation (HSCT) or had received induction and/or consolidation chemotherapy. A pulmonary CT scan was performed once weekly. Infiltrates were defined as either major or minor signs. IA was classified as proven, probable, or possible, in accordance with the definition stated by the European Organization for Research and Treatment of Cancer-Invasive Fungal Infections Cooperative Group and the National Institute of Allergy and Infectious Diseases Mycoses Study Group. Results. We analyzed 161 episodes of infection in 107 patients (65 allogeneic HSCT recipients, 30 autologous HSCT recipients, and 66 induction and/or consolidation chemotherapy recipients). A total of 109 episodes with no IA, 32 episodes with possible IA, and 20 episodes with probable or proven IA were identified. Minor pulmonary signs were detected by CT in 70 episodes (43%), and major pulmonary signs were detected by CT in 11 episodes (7%). Univariate and multivariate analyses revealed no significant association between detection of GM by EIA and detection of abnormal pulmonary signs by CT. A significant association was found between GM levels and receipt of piperacillin-tazobactam. GM test results were not positive before major signs were seen on CT images. Only 7 (10%) of 70 patients with minor pulmonary signs had positive GM test results before detection of the greatest pathologic change by CT. Conclusions. We show that detection of GM by EIA does not precede detection of major lesions by pulmonary CT. In the clinical setting, the decision to administer mold-active treatment should based on detection of new pulmonary infiltrates on CT performed early during infection, rather than on results of EIA for detection of G

Open Problems on Central Simple Algebras

We provide a survey of past research and a list of open problems regarding central simple algebras and the Brauer group over a field, intended both for experts and for beginners.Comment: v2 has some small revisions to the text. Some items are re-numbered, compared to v

A predictive score for retinopathy of prematurity in very low birth weight preterm infants

Aims This study describes the development of a score based on cumulative risk factors for the prediction of severe retinopathy of prematurity (ROP) comparing the performance of the score against the birth weight (BW) and gestational age (GA) in order to predict the onset of ROP.Methods A prospective cohort of preterm infants with BWp1500 g and/or GAp32 weeks was studied. the score was developed based on BW, GA, proportional weight gain from birth to the 6th week of life, use of oxygen in mechanical ventilation, and need for blood transfusions from birth to the 6th week of life. the score was established after linear regression, considering the impact of each variable on the occurrences of any stage and severe ROP. Receiver operating characteristic (ROC) curves were used to determine the best sensitivity and specificity values for the score. All variables were entered into an Excel spreadsheet (Microsoft) for practical use by ophthalmologists during screening sessions.Results the sample included 474 patients. the area under the ROC curve for the score was 0.77 and 0.88 to predict any stage and severe ROP, respectively. These values were significantly higher for the score than for BW (0.71) and GA (0.69) when measured separately.Conclusions ROPScore is an excellent index of neonatal risk factors for ROP, which is easy to record and more accurate than BW and GA to predict any stage ROP or severe ROP in preterm infants. the scoring system is simple enough to be routinely used by ophthalmologists during screening examination for detection of ROP. Eye (2012) 26, 400-406; doi: 10.1038/eye. 2011.334; published online 23 December 2011Hosp Clin Porto Alegre, Dept Ophthalmol, BR-90035903 Porto Alegre, RS, BrazilUniv Fed Rio Grande do Sul, Dept Ophthalmol, Sch Med, Porto Alegre, RS, BrazilUniversidade Federal de São Paulo, Dept Ophthalmol, Sch Med, São Paulo, BrazilUniv Fed Rio Grande do Sul, Dept Paediat, Newborn Sect, Sch Med, Porto Alegre, RS, BrazilUniversidade Federal de São Paulo, Dept Ophthalmol, Sch Med, São Paulo, BrazilWeb of Scienc

Defining motility in the Staphylococci

The ability of bacteria to move is critical for their survival in diverse environments and multiple ways have evolved to achieve this. Two forms of motility have recently been described for Staphylococcus aureus, an organism previously considered to be non-motile. One form is called spreading, which is a type of sliding motility and the second form involves comet formation, which has many observable characteristics associated with gliding motility. Darting motility has also been observed in Staphylococcus epidermidis. This review describes how motility is defined and how we distinguish between passive and active motility. We discuss the characteristics of the various forms of Staphylococci motility, the molecular mechanisms involved and the potential future research directions