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Jourdain E.,Roche Holding AG | Roques J.P.,Roche Holding AG | Chauvin M.,Roche Holding AG | Clark D.J.,Roche Holding AG | Clark D.J.,Createc Ltd
Astrophysical Journal | Year: 2012

Operational since 2002 on board the INTEGRAL observatory, the SPI spectrometer can be used to perform polarization measurements in the hard X-ray/softγ-ray domain (130 keV-8 MeV). However, this phenomenon is complex to measure at high energy and requires high fluxes. Cyg X-1 appears to be the best candidate amongst the X-ray binaries since it is one of the brightest persistent sources in this energy domain. Furthermore, a polarized component has recently been reported above 400 keV from IBIS data. We have therefore dedicated our efforts to developing the required tools to study the polarization in the INTEGRAL SPI data and have first applied them to 2.6 Ms of Cyg X-1 observations, covering 6.5 years of the INTEGRAL mission. We have found that the high energy emission of Cyg X-1 is indeed polarized, with a mean polarization fraction of 76% ± 15% at a position angle estimated to be 42°± 3°, for energies above 230 keV. The polarization fraction clearly increases with energy. In the 130-230 keV band, the polarization fraction is lower than 20%, but exceeds 75% between 370 and 850 keV, with the (total) emission vanishing above this energy. This result strongly suggests that the emission originates from the jet structure known to emit in the radio domain. The same synchrotron process could be responsible for the emission from radio to MeV, implying the presence of high energy electrons. This illustrates why the polarization of the high energy emission in compact objects is an increasingly important observational objective. © 2012. The American Astronomical Society. All rights reserved.


Chauvin M.,Toulouse 1 University Capitole | Chauvin M.,Roche Holding AG | Roques J.P.,Toulouse 1 University Capitole | Roques J.P.,Roche Holding AG | And 3 more authors.
Astrophysical Journal | Year: 2013

We present recent improvements in polarization analysis with the INTEGRAL SPI data. The SPI detector plane consists of 19 independent Ge crystals and can operate as a polarimeter. The anisotropy characteristics of Compton diffusions can provide information on the polarization parameters of the incident flux. By including the physics of the polarized Compton process in the instrument simulation, we are able to determine the instrument response for a linearly polarized emission at any position angle. We compare the observed data with the simulation sets by a minimum χ2 technique to determine the polarization parameters of the source (angle and fraction). We have tested our analysis procedure with Crab Nebula observations and find a position angle similar to those previously reported in the literature, with a comfortable significance. Since the instrument response depends on the incident angle, each exposure in the SPI data requires its own set of simulations, calculated for 18 polarization angles (from 0° to 170° in steps of 10°) and unpolarized emission. The analysis of a large number of observations for a given source, required to obtain statistically significant results, represents a large amount of computing time, but it is the only way to access this complementary information in the hard X-ray regime. Indeed, major scientific advances are expected from such studies since the observational results will help to discriminate between the different models proposed for the high energy emission of compact objects like X-ray binaries and active galactic nuclei or gamma-ray bursts. © 2013. The American Astronomical Society. All rights reserved.


Joyce M.J.,Lancaster University | Adams J.C.,Lancaster University | Heathcote J.A.,Dounreay Site Restoration Ltd DSRL | Mellor M.,Createc Ltd
Proceedings of Institution of Civil Engineers: Energy | Year: 2013

A key challenge in disposing of nuclear legacy facilities and planning a new nuclear plant is how to assess the extent or likelihood of radioactive contamination in construction materials and the ground. This paper summarises the status of two techniques based on the analysis of emitted radiation from materials that comprise such structures, and describes how this analysis can be used to infer the depth of contamination without the need to penetrate the structure or to destroy it in the process. Two experimental facilities have been developed to test the efficacy of these techniques, and data are provided for the most widespread contaminant experienced in the sector: caesium-137. Finally, the influence on the technique of the likely variety of silica-based media to be encountered in the nuclear industry is described, together with a summary of challenges to be addressed in future research.


Beaumont J.S.,Lancaster University | Mellor M.P.,Createc Ltd. | Villa M.,Vienna University of Technology | Joyce M.J.,Lancaster University | Joyce M.J.,Hybrid Instruments Ltd.
Nature Communications | Year: 2015

Knowledge of the neutron distribution in a nuclear reactor is necessary to ensure the safe and efficient burnup of reactor fuel. Currently these measurements are performed by in-core systems in what are extremely hostile environments and in most reactor accident scenarios it is likely that these systems would be damaged. Here we present a compact and portable radiation imaging system with the ability to image high-intensity fast-neutron and gamma-ray fields simultaneously. This system has been deployed to image radiation fields emitted during the operation of a TRIGA test reactor allowing a spatial visualization of the internal reactor conditions to be obtained. The imaged flux in each case is found to scale linearly with reactor power indicating that this method may be used for power-resolved reactor monitoring and for the assay of ongoing nuclear criticalities in damaged nuclear reactors. © 2015 Macmillan Publishers Limited.


PubMed | Lancaster University, Vienna University of Technology and Createc Ltd.
Type: | Journal: Nature communications | Year: 2015

Knowledge of the neutron distribution in a nuclear reactor is necessary to ensure the safe and efficient burnup of reactor fuel. Currently these measurements are performed by in-core systems in what are extremely hostile environments and in most reactor accident scenarios it is likely that these systems would be damaged. Here we present a compact and portable radiation imaging system with the ability to image high-intensity fast-neutron and gamma-ray fields simultaneously. This system has been deployed to image radiation fields emitted during the operation of a TRIGA test reactor allowing a spatial visualization of the internal reactor conditions to be obtained. The imaged flux in each case is found to scale linearly with reactor power indicating that this method may be used for power-resolved reactor monitoring and for the assay of ongoing nuclear criticalities in damaged nuclear reactors.


Beaumont J.,Lancaster University | Mellor M.P.,Createc Ltd. | Joyce M.J.,Lancaster University
Radiation protection dosimetry | Year: 2014

A new mixed-field imaging system has been constructed at Lancaster University using the principles of collimation and back projection to passively locate and assess sources of neutron and gamma-ray radiation. The system was set up at the University of Manchester where three radiation sources: (252)Cf, a lead-shielded (241)Am/Be and a (22)Na source were imaged. Real-time discrimination was used to find the respective components of the neutron and gamma-ray fields detected by a single EJ-301 liquid scintillator, allowing separate images of neutron and gamma-ray emitters to be formed. (252)Cf and (22)Na were successfully observed and located in the gamma-ray image; however, the (241)Am/Be was not seen owing to surrounding lead shielding. The (252)Cf and (241)Am/Be neutron sources were seen clearly in the neutron image, demonstrating the advantage of this mixed-field technique over a gamma-ray-only image where the (241)Am/Be source would have gone undetected. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.


Adams J.C.,Lancaster University | Mellor M.,Createc Ltd. | Joyce M.J.,Lancaster University
Environmental Science and Technology | Year: 2011

A method to determine the depth of buried localized radioactive contamination nonintrusively and nondestructively using principal component analysis is described. The γ-ray spectra from two radionuclides, cesium-137 and cobalt-60, have been analyzed to derive the two principal components that change most significantly as a result of varying the depth of the sources in a bespoke sand-filled phantom. The relationship between depth (d) and the angle (θ) between the first two principal component coefficients has been derived for both cases, viz.d(φ)=x+ylogeφwhere x and y are constants dependent on the shielding material and the γ-ray energy spectrum of the radioactivity in question, and φ is a function of θ. The technique enables the depth of a localized radioactive source to be determined nonintrusively in the range 5 to 50 mm with an accuracy of ±1 mm. © 2011 American Chemical Society.


Adams J.C.,Lancaster University | Joyce M.J.,Lancaster University | Mellor M.,Createc Ltd.
ANIMMA 2011 - Proceedings: 2nd International Conference on Advancements in Nuclear Instrumentation, Measurement Methods and their Applications | Year: 2011

A non-intrusive technique using principal component analysis, to infer the depth of the fission fragment caesium-137, when it is buried under silica sand has been described. Using energy variances within different γ-ray spectra, a complete depth model was produced for a single caesium-137 source buried under 1mm depths ranging between 5-50 mm. This was achieved using a cadmium telluride detector and a bespoke phantom. In this paper we describe the advancement of the technique by further validating it using blind tests for applications outside of the laboratory, where not only the depth (z) but also the surface (x, y) location of γ-ray emitting contamination is often poorly characterised. At present the technique has been tested at the point of maximum activity above the entrained γ-ray emitting source (where the optimal x, y location is known). This is not usually practical in poorly characterized environments where the detector cannot be conveniently placed at such an optimal location to begin with and scanning at multiple points around the region of interest is often required. Using a uniform scanning time, the point of maximum intensity can be located by sampling in terms of total count rate, and converging on this optimal point of maximum intensity. © 2011 IEEE.


Beaumont J.,Lancaster University | Mellor M.P.,Createc Ltd. | Joyce M.J.,Lancaster University
IEEE Nuclear Science Symposium Conference Record | Year: 2013

Passive imaging of fast neutrons has great potential in aiding the assessment of radiation environments. Knowledge of the spatial dependence of neutron flux allows the location of neutron sources to be deduced, additionally contributing the neutron components of radiation dosimetry calculations which can strongly impact strategies in scenarios such as decommissioning or accident response. Using the new prototype mixed-field imaging system at Lancaster University we have previously reported to the Nuclear Science Symposium in 2012 [1] the success of imaging sources of fast-neutron radiation and that neutron spectroscopy can be used alongside imaging techniques to identify different types of neutron sources. This research seeks to further investigate these applications by experimentally determining the resolving power of the system, in both imaging and radiation source recognition techniques. © 2013 IEEE.


Adams J.C.,Lancaster University | Joyce M.J.,Lancaster University | Mellor M.,Createc Ltd
Applied Radiation and Isotopes | Year: 2012

A phantom has been used to position two radiation sources, separately, when buried under dry-silica sand at depths between 5 and 50. mm. A γ-ray energy spectrum was then measured at every 1. mm depth. Principal component analysis has been conducted, which has led to a non-linear fit being established, allowing the depth of entrainment to be accurately inferred. The technique has been expanded for additional shielding media: water, aggregate and both wet and dry soil. The technique has also been expanded beyond the previous depth constraint of 50. mm. © 2011 Elsevier Ltd.

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