Mineral diagnostics: SEM-EDS Monte Carlo strategy for optimised measurements of ultrathin fragments in Cultural Heritage studies

The availability of minute quantities of sampling material is often an issue in the context of cultural heritage and archaeology due, for instance, to the value of the sample, its uniqueness or the small amount of residual material which testify the original form of the art to be restored. In this context, electron-excited energy-dispersive X-ray spectrometry (EDS) performed in a scanning electron microscope (SEM) has proven to be a primary methodology for analysing minute quantities of material thanks to its morphological and micro-analytical capability. However, when dealing with micro- and sub-micrometre specimens, as can be the case in ultrathin glass and metal fragments, several effects resulting from the physics and operational settings of the measurement must be considered to avoid quantification errors. In this paper, a detailed study of the effects of micro- and nanometric-sized glass and gold-alloy fragments on SEM-EDS microanalysis is presented. Monte Carlo simulations of different kinds of elongated glass fragment, with a square section and a thickness of 0.1 to 10 µm, and of some gold alloys demonstrated a strong influence in terms of the fragment size and operational conditions (beam energy, detector position, etc.). This work can be used to devise an appropriate and optimised measurement strategy.

A simulational study of the indirect-geometry neutron spectrometer BIFROST at the European Spallation Source, from neutron source position to detector position

The European Spallation Source (ESS) is intended to become the most powerful spallation neutron source in the world and the flagship of neutron science in upcoming decades. The exceptionally high neutron flux will provide unique opportunities for scientific experiments but also set high requirements for the detectors. One of the most challenging aspects is the rate capability and in particular the peak instantaneous rate capability, i.e. the number of neutrons hitting the detector per channel or cm2 at the peak of the neutron pulse. The primary purpose of this paper is to estimate the incident rates that are anticipated for the BIFROST instrument planned for ESS, and also to demonstrate the use of powerful simulation tools for the correct interpretation of neutron transport in crystalline materials. A full simulation model of the instrument from source to detector position, implemented with the use of multiple simulation software packages, is presented. For a single detector tube, instantaneous incident rates with a maximum of 1.7 GHz for a Bragg peak from a single crystal and 0.3 MHz for a vanadium sample are found. This paper also includes the first application of a new pyrolytic graphite model and a comparison of different simulation tools to highlight their strengths and weaknesses.

Spectroscopic Characterization of Laser Ablated Germanium Plasma

In the present study, the germanium (Ge) sample has been studied by laser induced breakdown spectroscopy which leads to the formation of plasma plume in the air. This research work comprises on pure Ge sample, and it has been studied using laser irradiance 1.831011 watt.cm-2 and Q-Switched Nd:YAG laser pulse (λ ~ 1064 nm wavelength and  ~ 5 ns pulse width). The spatially resolved plasma plume parameters are investigated, such as variation of electron temperature Te and electron number density ne as a function of detector position. These parameters show variation in the plasma plume and yield electron temperature Te from 12340 to 7640 ± 1200 K. Whereas electron number density ne varies from 3.61017 to 1.601017 cm-3 with the change in detector position is moving away from plasma plume from 0 to 3 mm. The results show that electron temperature Te and electron number density ne are estimated from the Boltzmann plot method and by using Lorentzian function at spectral line using FWHM full width at half maximum at 265.11 nm (4p5s 3 p2 → 4p 2 3 p2) wavelength of Ge (I) line, respectively.

Position evaluation of ex-core neutron flux measurement in new type graphite reactors

Several concepts of new reactors use graphite. Some of them use graphite as a moderator, some of them as a reflector. There are at least two concepts of these graphitetype reactors under development in the Czech Republic. Both reactors use graphite as the reflector. An in-core measurement might be impossible to use because of various reasons, for instance, high temperature or aggressive environment. Therefore, this article focuses on ex-core neutron flux measurement system placed in the graphite reflector and the optimization of ex-core detector position. A set of experiments were performed at LR-0 reactor. The LR-0 is a light water reactor with a well-defined neutron field, which can be used for different material insertion tests and testing of its influence on criticality. Several modifications of LR-0 cores were modelled in Monte Carlo codes Serpent and KENO. A set of calculations were performed for verification of the criticality and neutron flux course in the reactor core and graphite reflector. Further investigation was focused on the influence of the presence of a graphite reflector on the neutron distribution in the reactor core. The LR-0 graphite experiments were also used to verify the calculations. Based on the results of this article, the optimal position of ex-core detectors in the graphite reflector is proposed.

Quantification and correction of the scattered X-rays from a megavoltage photon beam to a linac-mounted kilovoltage imaging subsystem

Objective: To quantify and correct megavoltage (MV) scattered X-rays (MV-scatter) on an image acquired using a linac-mounted kilovoltage (kV) imaging subsystem. Methods and materials: A linac-mounted flat-panel detector (FPD) was used to acquire an image containing MV-scatter by activating the FPD only during MV beam irradiation. 6-, 10-, and 15 MV with a flattening-filter (FF; 6X-FF, 10X-FF, 15X-FF), and 6- and 10 MV without an FF (6X-FFF, 10X-FFF) were used. The maps were acquired by changing one of the irradiation parameters while the others remained fixed. The mean pixel values of the MV-scatter were normalized to the 6X-FF reference condition (MV-scatter value). An MV-scatter database was constructed using these values. An MV-scatter correction experiment with one full arc image acquisition and two square field sizes (FSs) was conducted. Measurement- and estimation-based corrections were performed using the database. The image contrast was calculated at each angle. Results: The MV-scatter increased with a larger FS and dose rate. The MV-scatter value factor varied substantially depending on the FPD position or collimator rotation. The median relative error ranges of the contrast for the image without, and with the measurement- and estimation-based correction were −10.9 to −2.9, and −1.5 to 4.8 and −7.4 to 2.6, respectively, for an FS of 10.0 × 10.0 cm2. Conclusions: The MV-scatter was strongly dependent on the FS, dose rate, and FPD position. The MV-scatter correction improved the image contrast. Advances in knowledge: The MV-scatters on the TrueBeam linac kV imaging subsystem were quantified with various MV beam parameters, and strongly depended on the fieldsize, dose rate, and flat panel detector position. The MV-scatter correction using the constructed database improved the image quality.

Fission chambers for space effect reduction in the application of the area method: A new approach

The possibility of preparing fission chambers for the experimental determination of subcriticality without time-consuming corrections has been presented. The reactor detectors set consists of monoisotopic chambers. Each chamber is intended for a specific position in the system. Individual weights, rated a priori for all detectors in their positions, allow for quick calculation of whole system subcriticality. The inconveniences related to the spatial effect are minimized. This is achieved by computational simulation of the area method results, for each detector position and all possible fissionable and fissile nuclides. Next, one nuclide is selected, specific for the given position, presenting the smallest difference from the MCNP KCODE precisely estimated kkcode. The case study is made using the model of VENUS-F core.

Freeform Mirror Design for Novel Laser Warning Receivers and Laser Angle of Incidence Sensors

In this paper, we present a novel configuration of an optical angle-of-incidence (AOI) sensor based on the application of a freeform mirror. The main challenge in designing this mirror was to provide a strictly linear transformation between AOI and the spatial position of the spot created on the linear detector array. Another two goals of this paper were to minimize stray light issues (improve the dynamic range) and create an intermediate focus and lateral shift in the detector position with respect to the plane of incidence. From an optical point of view, the designed mirror can thus be understood as the composition of three components: a high-numerical-aperture (NA) fully achromatic f-theta lens in one cross-section and a perfectly focusing lens, combined with a deviating prism in the second (orthogonal) cross-section. In comparison to the standard “shade” methods, the proposed approach allows a constant angular resolution to be maintained over the entire field of view. The mirror was designed on the basis of fundamental geometrical rules by numerically solving differential problems using an innovative scheme based on the minimization of the specific merit function. The proposed method was practically applied to design a freeform mirror for a 90°/120° field-of-view sensor, showing a satisfactory performance.