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1.
  • Marcelli, N., et al. (author)
  • Time Dependence of the Flux of Helium Nuclei in Cosmic Rays Measured by the PAMELA Experiment between 2006 July and 2009 December
  • 2020
  • In: Astrophysical Journal. - : IOP PUBLISHING LTD. - 0004-637X .- 1538-4357. ; 893:2
  • Journal article (peer-reviewed)abstract
    • Precise time-dependent measurements of the Z = 2 component in the cosmic radiation provide crucial information about the propagation of charged particles through the heliosphere. The PAMELA experiment, with its long flight duration (2006 June 15-2016 January 23) and the low energy threshold (80 MeV/n) is an ideal detector for cosmic-ray solar modulation studies. In this paper, the helium nuclei spectra measured by the PAMELA instrument from 2006 July to 2009 December over a Carrington rotation time basis are presented. A state-of-the-art three-dimensional model for cosmic-ray propagation inside the heliosphere was used to interpret the time-dependent measured fluxes. Proton-to-helium flux ratio time profiles at various rigidities are also presented in order to study any features that could result from the different masses and local interstellar spectra shapes.
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2.
  • Morris, Richard J.H., et al. (author)
  • Field dependent study on the impact of co-evaporated multihits and ion pile-up for the apparent stoichiometric quantification of GaN and AlN
  • 2022
  • In: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 241
  • Journal article (peer-reviewed)abstract
    • For atom probe tomography, multihits and any associated ion pile-up are viewed as an “Achilles” heel when trying to establish accurate stoichiometric quantification. A significant reason for multihits and ion pile-up is credited to co-evaporation events. The impact is the underestimation of one or more elements present due to detector inadequacies when the field evaporated ions are spatially and temporally close. Nitride materials, especially GaN and AlN, have been shown to suffer a strong field dependent compositional bias, with N having the characteristics for being a species prone to ion pile-up. In this paper we have explored through field dependent measurements on GaN and AlN the associated impact of co-evaporated multihits and ion pile-up. To achieve this a normal CAMECA electrode along with a specially modified GRID electrode, which was designed to manipulate co-evaporated ions and hence ion pile-up, were employed. From our results and in-depth analysis, any co-evaporation and associated ion pile-up is found to be either very small, or not species dependent. Thus, ion pile-up cannot be attributed as the cause for the significant N underestimation observed in these materials.
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