Localisation of gamma-ray interaction points in thick monolithic CeBr3 and LaBr3:Ce scintillators

Localisation of gamma-ray interaction points in monolithic scintillator crystals can simplify the design and improve the performance of a future Compton telescope for gamma-ray astronomy. In this paper we compare the position resolution of three monolithic scintillators: a 28x28x20 mm3 (length x breadth x thickness) LaBr3:Ce crystal, a 25x25x20 mm3 CeBr3 crystal and a 25x25x10 mm3 CeBr3 crystal. Each crystal was encapsulated and coupled to an array of 4x4 silicon photomultipliers through an optical window. The measurements were conducted using 81 keV and 356 keV gamma-rays from a collimated 133Ba source. The 3D position reconstruction of interaction points was performed using artificial neural networks trained with experimental data. Although the position resolution was significantly better for the thinner crystal, the 20 mm thick CeBr3 crystal showed an acceptable resolution of about 5.4 mm FWHM for the x and y coordinates, and 7.8 mm FWHM for the z-coordinate (crystal depth) at 356 keV. These values were obtained from the full position scans of the crystal sides. The position resolution of the LaBr3:Ce crystal was found to be considerably worse, presumably due to the highly diffusive optical in- terface between the crystal and the optical window of the enclosure. The energy resolution (FWHM) measured for 662 keV gamma-rays was 4.0% for LaBr3:Ce and 5.5% for CeBr3. The same crystals equipped with a PMT (Hamamatsu R6322-100) gave an energy resolution of 3.0% and 4.7%, respectively

Characterization of a CCD array for Bragg spectroscopy

The average pixel distance as well as the relative orientation of an array of 6 CCD detectors have been measured with accuracies of about 0.5 nm and 50 $\mu$rad, respectively. Such a precision satisfies the needs of modern crystal spectroscopy experiments in the field of exotic atoms and highly charged ions. Two different measurements have been performed by illuminating masks in front of the detector array by remote sources of radiation. In one case, an aluminum mask was irradiated with X-rays and in a second attempt, a nanometric quartz wafer was illuminated by a light bulb. Both methods gave consistent results with a smaller error for the optical method. In addition, the thermal expansion of the CCD detectors was characterized between -105 C and -40 C.Comment: Submitted to Review of Scientific Instrument

Localisation of gamma-ray interaction points in thick monolithic cebr3 and labr3:ce scintillators

Localisation of gamma-ray interaction points in monolithic scintillator crystals can simplify the design and improve the performance of a future Compton telescope for gamma-ray astronomy. In this paper we compare the position resolution of three monolithic scintillators: a 28x28x20 mm(3) (lengthxbreadth x thickness) LaBr3:Ce crystal, a 25x25x20 mm(3) CeBr3 crystal and a 25x25x10 mm(3) CeBr3 crystal. Each crystal was encapsulated and coupled to an array of 4x4 silicon photomultipliers through an optical window. The measurements were conducted using 81 keV and 356 keV gamma-rays from a collimated Ba-133 source. The 3D position reconstruction of interaction points was performed using artificial neural networks trained with experimental data. Although the position resolution was significantly better for the thinner crystal, the 20 mm thick CeBr3 crystal showed an acceptable resolution of about 5.4 mm FWHM for the x and y coordinates, and 7.8 mm FWHM for the z-coordinate (crystal depth) at 356 keV. These values were obtained from the full position scans of the crystal sides. The position resolution of the LaBr3: Ce crystal was found to be considerably worse, presumably due to the highly diffusive optical interface between the crystal and the optical window of the enclosure. The energy resolution (FWHM) measured for 662 keV gamma-rays was 4.0% for LaBr3: Ce and 5.5% for CeBr3. The same crystals equipped with a PMT (Hamamatsu R6322-100) gave an energy resolution of 3.0% and 4.7%, respectively

IR detectors for the GERB instrument on MSG.

The Geostationary Earth Radiation Budget (GERB) instrument is to be flown on ESA’s Meteosat Second Generation (MSG) satellite in 2000. The purpose of the instrument is to measure accurately the daily cycle of the reflected and emitted radiation of the Earth over at least a five year period. The measurements will be made from geostationary orbit and will complement those planned from instruments in low Earth polar orbits. The data from GERB will provide the first consistent measurements of the hour-by-hour variation of clouds and simultaneous measurements of the radiation balance, and will allow climate models to be further developed and validated. The instrument will accumulate images of the Earth disc every 15 minutes in wavebands of 0.32 - 4.0 m and 0.32 - 30 m with a nadir resolution of 50 km. The detector for this instrument consists of a 256 pixel linear array of thermoelectric (TE) elements. The TE array operates at room temperature and is blacked to give a flat spectral response over the 0.32 - 30 m band. The detector hybrid consists of the 256 pixel detector plus 4 Application Specific Integrated Circuits (ASICs), comprising 64 channels each, which perform front end analogue signal processing, A/D conversion and multiplexing. As the MSG platform is spin-stabilised, the Earth image is stabilised on the detector using a de-spin mirror and is only present on the detector for 40 ms. Integration of the signal over the 40 ms and taken over a 15 minute observation period enables the radiance in both long and short wavebands to be measured to an accuracy better than 1%. The detector concept is described and test results of a prototype system are presented

Registration by interactive inverse simulation: application for adaptive radiotherapy

International audiencePurpose. This paper introduces a new methodology for semi-automatic registration of anatomical structure deformations. The contribution is to use an interactive inverse simulation of physics-based deformable model, computed in real-time. Methods. The method relies on non-linear Finite Element Method (FEM) within a constraint-based framework. Given a set of few registered points provided by the user, a real-time optimization adapts the boundary conditions and(/or) some parameters of the FEM in order to obtain the adequate geometrical deformations. To dramatically fasten the process, the method relies on a projection of the model in the space of the optimization variables. In this reduced space, a quadratic programming problem is formulated and solved very quickly. The method is validated with numerical examples for retrieving some unknown parameters such as the Young's modulus and some pressures on the boundaries of the model. Results. The approach is employed it in the context of radiotherapy of the neck where weight loss during the 7 weeks of the therapy modifies the volume of the anatomical structures and induces large deformations. Indeed sensitive structures such as the parotid glands may cross the target volume due to these deformations which leads to adverse effects for the patient. We thus apply the approach for the registration of the parotid glands during the radiotherapy of the head and neck cancer. 2 Eulalie Coevoet et al. Conclusions. The results show how the method could be used in a clinical routine and be employed in the planning in order to limit the radiations of these glands

Performance characteristics of the PAW instrumentation on Beagle 2 (the astrobiology lander on ESA's Mars Express Mission)

The performance of the PAW instrumentation on the 60kg Beagle 2 lander for ESA’s 2003 Mars Express mission will be described. Beagle 2 will search for organic material on and below the surface of Mars in addition to a study of the inorganic chemistry and mineralogy of the landing site. The lander will utilize acquisition and preparation tools to obtain samples from below the surface, and both under and inside rocks. In situ analysis will include examination of samples with an optical microscope, Mossbauer and fluorescent X-ray spectrometers. Extracted samples will be returned to the lander for analysis, in particular a search for organics and a measurement of their isotopic composition. The PAW experiment performance data will be described along with the status of the project

Defence contractors and diversification into the civil sector: Rolls-Royce, 1945-2005

A number of studies have shown that defence contractors have exhibited a marked reluctance to diversify away from defence and develop civil applications. However, the aero engine manufacturer Rolls-Royce is one defence contractor to which this does not apply. Over a 60-year period it has moved from being almost entirely dependent on defence work to a point where defence now constitutes barely one-fifth of its turnover. This article examines the development of the company's civil aerospace business over the period since 1945. It focuses specifically on the strategies used by Rolls-Royce in the civil aerospace field. These strategies are explored in the context of changes in market conditions, technology, and governance arrangements. The effectiveness of the various strategies, including their contribution to the company's current position, is evaluated.Aerospace Industry, Defence Diversification, Strategy, Technology, Gas Turbine, Rolls-Royce,