Graeme M. Hansford

A lightweight near-infrared spectrometer for the detection of trace atmospheric species

This paper describes the development and deployment of a lightweight in situ near-infrared tunable diode laser absorption spectrometer (TDLAS) for balloon-borne measurements of trace species such as methane in the upper troposphere and stratosphere. The key feature of the instrument design is its ability to provide high sensitivity measurements with better than 1 part in 10(6) Hz(-1/2) optical sensitivity in a lightweight package weighing as little as 6 kg, and maintaining this level of performance over the wide range of conditions experienced during field measurements. The absolute accuracy for methane measurements is approximately 10% limited by uncertainties in determining the gas temperature in the measurement volume. The high sensitivity and high temporal resolution (2.3 s measurement period) enables details of the fine-scale structure in the atmosphere to be measured. The TDLAS instrument has been used on a number of major international measurement campaigns. Intercomparison with other instruments during these campaigns have confirmed the comparability of the results from this instrument with measurements made by a range of other techniques, and demonstrated the instruments suitability for studies of atmospheric dynamics, transport, and mixing processes.

Infrared laser spectroscopy of jet-cooled methyl manganese pentacarbonyl

Infrared absorption spectra of jet‐cooled CH3Mn(CO)5 and CD3Mn(CO)5 in the region of the two strongly allowed CO vibrations have been measured using diode lasers. Analysis of the spectra yielded values for the band centers and rotational constants for parallel bands of both isotopic species, and for the perpendicular band of CH3Mn(CO)5; the latter also provided an estimate of the Coriolis constant for this vibration. The spectra were consistent with essentially free rotation of the methyl group. The rotational constants were in close agreement with those derived from electron diffraction data: however, the B‐rotational constants provide a revised estimate for the axial Mn–CO bond length.

Planetary science and exploration in the deep subsurface : results from the MINAR Program, Boulby Mine, UK

The authors would also like to acknowledge the funding provided by the STFC Impact Acceleration Fund. Claire R. Cousins is supported by a Royal Society of Edinburgh Research Fellowship. The development of the ExoMars PanCam, the AUPE2 system and the PanCam data processing pipeline has been supported by funding from the UK Space Agency (lead funding agency) and the European Community’s Seventh Framework Program.

PoDFluX: a new Monte Carlo ray-tracing model for powder diffraction and fluorescence.

PoDFluX is a new Monte Carlo ray-tracing program that simulates from first principles x-ray powder diffraction from crystalline materials and x-ray fluorescence from materials with a defined elemental composition. This model has been written primarily for the optimization of miniaturized planetary x-ray diffraction instrumentation but wider applications are certainly possible. A particular strength of the model is the implementation of several variance-reduction techniques for the minimization of execution times. Comparisons of model output with experimental diffraction and fluorescence data show good quantitative agreement.

Back-reflection energy-dispersive X-ray diffraction: A novel diffraction technique with almost complete insensitivity to sample morphology

A novel X-ray diffraction (XRD) technique, which exhibits almost complete insensitivity to the morphology of and distance to the sample, is presented for the first time. This technique applies energy-dispersive XRD (EDXRD) in a back-reflection geometry, with 2θ ≃ 180°. Although this geometry leads to low resolution of diffraction peaks and the greatest overlap with fluorescence peaks, it nevertheless yields a combination of properties that are unique in the field of X-ray diffractometry. It is likely that diffraction patterns can be obtained with no or very minimal sample preparation. Furthermore, the intrinsic geometry of the method and the simplicity inherent to EDXRD enables a compact lightweight instrument design, suitable for field-portable or hand-held XRD and X-ray fluorescence analysis. Application to geological and planetary science is emphasized in this paper. The characteristics of the technique are elucidated via theoretical considerations and ray-trace modelling, and the simplest possible implementation is described.

The suppression of fluorescence peaks in energy-dispersive X-ray diffraction

A novel method to separate diffraction and fluorescence peaks in energy-dispersive X-ray diffraction (EDXRD) is described. By tuning the excitation energy of an X-ray tube source to just below an elemental absorption edge, the corresponding fluorescence peaks of that element are completely suppressed in the resulting spectrum. Since Bremsstrahlung photons are present in the source spectrum up to the excitation energy, any diffraction peaks that lie at similar energies to the suppressed fluorescence peaks are uncovered. This technique is an alternative to the more usual method in EDXRD of altering the scattering angle in order to shift the energies of the diffraction peaks. However, in the back-reflection EDXRD technique [Hansford (2011). J. Appl. Cryst. 44, 514–525] changing the scattering angle would lose the unique property of insensitivity to sample morphology and is therefore an unattractive option. The use of fluorescence suppression to reveal diffraction peaks is demonstrated experimentally by suppressing the Cau2005K fluorescence peaks in the back-reflection EDXRD spectra of several limestones and dolomites. Three substantial benefits are derived: uncovering of diffraction peak(s) that are otherwise obscured by fluorescence; suppression of the Cau2005K escape peaks; and an increase in the signal-to-background ratio. The improvement in the quality of the EDXRD spectrum allows the identification of a secondary mineral in the samples, where present. The results for a pressed-powder pellet of the geological standard JDo-1 (dolomite) show the presence of crystallite preferred orientation in this prepared sample. Preferred orientation is absent in several unprepared limestone and dolomite rock specimens, illustrating an advantage of the observation of rocks in their natural state enabled by back-reflection EDXRD.

High-resolution X-ray diffraction with no sample preparation

A novel, high-resolution X-ray diffraction (XRD) technique that provides completely non-destructive, high-quality XRD analyses of unprepared samples is demonstrated. The method shows great potential in the characterization of cultural heritage artefacts.

Phase-targeted X-ray diffraction

A method to enhance the X-ray diffraction signal of a specific targeted crystalline phase within a sample is presented. This technique can be implemented in a handheld or in-line instrument format.