74 research outputs found
Design and characterisation of metallic glassy alloys of high neutron shielding capability
This paper reports the design, making and characterisation of a series of Fe-based bulk metallic glass alloys with the aim of achieving the combined properties of high neutron absorption capability and sufficient glass forming ability. Synchrotron X-ray diffraction and pair distribution function methods were used to characterise the crystalline or amorphous states of the samples. Neutron transmission and macroscopic attenuation coefficients of the designed alloys were measured using energy resolved neutron imaging method and the very recently developed microchannel plate detector. The study found that the newly designed alloy (Fe48Cr15Mo14C15B6Gd2 with a glass forming ability of Ø5.8 mm) has the highest neutron absorption capability among all Fe-based bulk metallic glasses so far reported. It is a promising material for neutron shielding applications
A high resolution, high frame rate detector based on a microchannel plate read out with the Medipix2 counting CMOS pixel chip.
The future of ground-based optical astronomy lies with advancements in adaptive optics (AO) to overcome the limitations that the atmosphere places on high resolution imaging. A key technology for AO systems on future very large telescopes are the wavefront sensors (WFS) which detect the optical phase error and send corrections to deformable mirrors. Telescopes with >30 m diameters will require WFS detectors that have large pixel formats (512x512), low noise (<3 e-/pixel) and very high frame rates (~1 kHz). These requirements have led to the idea of a bare CMOS active pixel device (the Medipix2 chip) functioning in counting mode as an anode with noiseless readout for a microchannel plate (MCP) detector and at 1 kHz continuous frame rate. First measurement results obtained with this novel detector are presented both for UV photons and beta particles
CalFUSE v3: A Data-Reduction Pipeline for the Far Ultraviolet Spectroscopic Explorer
Since its launch in 1999, the Far Ultraviolet Spectroscopic Explorer (FUSE)
has made over 4600 observations of some 2500 individual targets. The data are
reduced by the Principal Investigator team at the Johns Hopkins University and
archived at the Multimission Archive at Space Telescope (MAST). The
data-reduction software package, called CalFUSE, has evolved considerably over
the lifetime of the mission. The entire FUSE data set has recently been
reprocessed with CalFUSE v3.2, the latest version of this software. This paper
describes CalFUSE v3.2, the instrument calibrations upon which it is based, and
the format of the resulting calibrated data files.Comment: To appear in PASP; 29 pages, 13 figures, uses aastex, emulateap
Synchrotron Microtomography and Neutron Radiography Characterization of the Microstruture and Water Absorption of Concrete from Pompeii
There is renewed interest in using advanced techniques to characterize
ancient Roman concrete. In the present work, samples were drilled from the
"Hospitium" in Pompeii and were analyzed by synchrotron microtomography (uCT)
and neutron radiography to study how the microstructure, including the presence
of induced cracks, affects their water adsorption. The water distribution and
absorptivity were quantified by neutron radiography. The 3D crack propagation,
pore size distribution and orientation, tortuosity, and connectivity were
analyzed from uCT results using advanced imaging methods. The concrete
characterization also included classical methods (e.g., differential
thermal-thermogravimetric, X-ray diffractometry, and scanning electron
microscopy). Ductile fracture patterns were observed once cracks were
introduced. When compared to Portland cement mortar/concrete, Pompeii samples
had relatively high porosity, low connectivity, and similar coefficient of
capillary penetration. In addition, the permeability was predicted from models
based on percolation theory and the pore structure data to evaluate the fluid
transport properties
Single photon imaging at ultra-high resolution
Abstract We present a detection system capable of imaging both single photon/positive ion and multiple coincidence photons/positive ions with extremely high spatial resolution. In this detector the photoelectrons excited by the incoming photons are multiplied by microchannel plate(s) (MCP). The process of multiplication is spatially constrained within an MCP pore, which can be as small as 4 μm for commercially available MCPs. An electron cloud originated by a single photoelectron is then encoded by a pixellated custom analog ASIC consisting of 105 K charge sensitive pixels of 50 μm in size arranged on a hexagonal grid. Each pixel registers the charge with an accuracy o
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