PIXE Group Current and Recent Research

Our research continues to revolve around particle-induced X-ray emission (PIXE) both in the Guelph Pelletron Accelerator Lab and on the Mars Science Lab’s Curiosity rover. GUPIX development continues, as does our derived GUAPX code for the Mars rover alpha particle X-ray spectrometers.

  • We have improved the accuracy of PIXE analysis of major and minor elements in mono-mineralic rocks to the level of 1-2%. This involved projects which are described in the PhD thesis of Chris Heirwegh (now research staff member at Cal Tech):
    (i) comparison of PIXE yields from light elements with GUYLS predictions in which both XCOM and FFAST mass attenuation coefficients were used; the outcome was a new blended MAC database for GUPIX;
    (ii) development of a correction within GUPIX for non-linear channel-energy response in SDDs.
    Since then, MSc student Dan Cureatz has developed an elegant computer tool which can determine the parameters of the above correction.

  • Working with Chris Heirwegh during his PDF period and Brianna Ganly (visitor from CSIRO, Australia), we have improved the quality of GUAPX fits to spectra from the Curiosity rover’s alpha particle X-ray spectrometer; this necessitated solving the problem of apparent energy shifts of light element X-rays. These shifts arise from two sources:  non-linearity and alpha-induced multiple ionization satellites. A database for MIS has been constructed and incorporated into GUAPX; it will also be incorporated in GUPIX for terrestrial alpha-PIXE.

  • We are presently collaborating with Matjasz Kavčič (Institute Josef Stefan, Slovenia) and Stjepko Fazinič (Ruder Boskovič Institute, Croatia) and their local colleagues on further development of the MIS database mentioned above. This involves high-resolution wavelength-dispersive X-ray at the IJS and RBI ion beam facilities. Work on Ti is complete and measurements on K, Cl, Ca, Cr, Fe are being scheduled for summer 2019

  • In collaboration with G.M. Perrett at Cornell University we succeed in quantitative prediction from first principles (geochemical, mineralogical and physical) of the mineral phase effects upon APXS analytical results for light elements. These effects were first reported by us following our 2012 fundamental parameters calibration of the Curiosity APXS.

  • Development of a Monte Carlo simulate program to predict X-ray yields generated by APXS was started by MSc student David Thomson and concluded by Erin Flannigan and Dustin Tesselaar.  The predictions for moo-mineral standards agreed closely with our 2012 APXS calibration measurements, and thus provided strong support for our fundamental parameters approach. 

  • The MSc thesis work of Erin Flannigan involved the development and calibration of an accelerator-based PIXE system which would emulate the Mars APXS. It was used by her to measure the mineral phase effects first noted in geo-standards during calibration of the Curiosity APXS. Excellent agreement was found between PIXE and APXS, and the APXS calibration was “expanded” by adding new rock types (e.g. basaltic trachy-andesites) to the geostandard suite.

  • In collaboration with Dr Jeff Berger we have applied the PIXE Emulator System in a study of 65 weathered Hawaiian rocks which appear to emulate formations seen by Curiosity in Gale Crater. The work demonstrates the system’s potential for study of terrestrial analogues of Martian rocks. These rocks were analyzed for us also by borate fusion XRF thereby enabling us to use them as secondary standards. MS student Leanne Sargent is using these to extend the emulator calibration to “GRMs” having high Mg content.  

  • Leanne has also installed and calibrated a Si(Li) X-ray detector which has enabled us to extend the emulation work to trace elements.

  • With Dr Perrett and Dustin Tesselaar, together with Prof. Mariek Schmidt and her students at Brock university, we have devised a method for correcting the APXS analysis of Martian rocks for the ubiquitous thin layer of wind-blown dust that is typically present. The method uses the “as is” APXS spectrum of the rock plus a second spectrum acquired after brushing as much of the deposit off as possible (100% removal is not possible). The first round of this work was done with Gale Crater mudstones. The converse approach has been demonstrated, analyzing a thin dark layer deposited by fluids on the Mazatzal sample examined in the early days of the Spirit Rover at Gusev Crater.

  • A major project is underway to upgrade GUPIXWIN to GUPIX-3. This involves many new features including database improvements and extensions.

  • We have developed a new code GUMAP which will assist workers doing micro-PIXE imaging. The user can construct 2D element maps from Oxford Microbeams list mode files and then select small regions of interest on her monitor. For each of these a PIXE spectrum is created which can be sent to GUPIXWIN for determination of element concentrations.