Measurement of energies and intensities of multiple ionization satellite (MIS) excited in light elements by helium ion beams

TNA project number: 19001708-ST

Measurement of energies and intensities of multiple ionization satellite (MIS) excited in light elements by helium ion beams

Scientific background:

Over 1600 X-ray spectra have been collected from the alpha particle X-ray spectrometers on Mars rovers including the present Curiosity rover. The spectra are excited by the radionuclide ²⁴⁴Cm, which emits 5 MeV He ions for PIXE and Pu L X-rays for XRF. These spectra provide elemental analysis of rocks, soils and dust as part of the quest to identify formerly habitable (water-bearing) environments. Applicant is a member of the Curiosity APXS team within NASA’s Mars Science Laboratory. Excitation of K X-rays by 5 MeV He ions produces also energy-shifted satellites due to 1, 2 or 3 L-shell spectator vacancies. These cause significant distortion of the diagram lines and worsen the quality of spectrum fits by the GUPIX(Mars) code. An MIS database is needed to support a correction procedure that is already devised. This work will increase analytical accuracy and will also support more accurate terrestrial PIXE analysis using alpha beams, especially when partnered with RBS; this could lead to increased use of these two IBA methods in a complementary manner.

Measurements performed within TNA project:

The wavelength-dispersive in-vacuum x-ray spectrometer of J. Stefan Institute (Ljubljana, Slovenia) [1] have been used to record high energy resolution KaL^N X-ray spectra of Ca and Cr induced in collisions with MeV alpha particles. The targets used were metallic Cr, Cr₂O₃, and CaF₂. The KaL^N X-ray spectra of Cr and Cr₂O₃ were measured using three different energies of He ions, namely 3 MeV, 4 MeV and 5 MeV. For CaF₂ we have collected only spectra induced with 5 MeV He beam. The main purpose of the experiment was to record KaL^N spectra with good enough statistics to determine precisely energy/intensity of the corresponding satellite lines. The results for the energy shifts and relative intensities of the groups will be incorporated in the MIS database providing an empirical means for inclusion of one peak per satellite group when modelling energy-dispersive spectra (GUPIX(Mars) code).

[1] M. Kavčič, M. Budnar, A. Mühleisen, F. Gasser, M. Žitnik, K. Bučar, R. Bohinc, Design and performance of a versatile curved-crystal spectrometer for high-resolution spectroscopy in the tender x-ray range, Rev. Sci. Instr. 83, 033113 (2012). http://dx.doi.org/10.1063/1.3697862

Data files:

We are sharing the detector files (a series of single exposure 2D raw images) collected by the Andor DX438-BV CCD camera (770 × 1152 pixels with pixel size 22.5×22.5 μm²) after the diffraction on the crystal analyzer. The horizontal axis of the detector corresponds to the dispersion axis and diffracted photons are detected at different horizontal positions according to their wavelength, the vertical axis of the detector serves mainly to accumulate more statistics. The final emission spectra are obtained from the corresponding detector files using the home-written data processing software.