THERMAL MODEL FOR THE DESORPTION OF (MOLECULAR) IONS INDUCED BY MeV HEAVY IONS

H. VOIT; E. NIESCHLER; B. NEES; R. SCHMIDT; CH. SCHOPPMANN; P. BEINING; J. SCHEER

doi:10.1051/jphyscol:1989238

Movement of secondary electrons due to the irradiation of heavy ions: Role of the composite electric field formed from the polarization of molecules and molecular ions

Radiation Physics and Chemistry ◽

10.1016/j.radphyschem.2012.10.015 ◽

2013 ◽

Vol 85 ◽

pp. 36-41 ◽

Cited By ~ 13

Author(s):

Kengo Moribayashi

Keyword(s):

Electric Field ◽

Heavy Ions ◽

Molecular Ions ◽

Secondary Electrons

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Heavy positive ion groups in Titan's ionosphere: Cassini Plasma Spectrometer IBS observations

10.5194/egusphere-egu21-2726 ◽

2021 ◽

Author(s):

Richard Haythornthwaite ◽

Andrew Coates ◽

Geraint Jones ◽

Anne Wellbrock ◽

Hunter Waite ◽

...

Keyword(s):

Heavy Ions ◽

Ion Beam ◽

Negative Ions ◽

Molecular Ions ◽

Upper Atmosphere ◽

High Mass ◽

Aerosol Formation ◽

Polycyclic Aromatic ◽

Plasma Spectrometer ◽

Positive Ion

IntroductionTitan is the largest moon of Saturn and has a thick extended atmosphere along with a large ionosphere. Titan's ionosphere contains a plethora of hydrocarbons and nitrile cations and anions as measured by the Ion Neutral Mass Spectrometer and Cassini Plasma Spectrometer (CAPS) onboard the Cassini spacecraft1.Previous ion composition studies in Titan&#8217;s ionosphere by Cassini instruments revealed "families" of ions around particular mass values and a regular spacing of 12 to 14 u/q between mass groups 2. These are thought to be related to a carbon or nitrogen backbone that dominates the ion chemistry2. Previous studies also identified possible heavy ions such as naphthalene, anthracene derivatives and an anthracene dimer at 130, 170 and 335 u/q respectively1.&#160;&#160;Methodology&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; The CAPS Ion Beam Spectrometer3 is an electrostatic analyser that measures energy/charge ratios of ions. During the Titan flybys Cassini had a high velocity (~6 km/s) relative to the low ion velocities (< 230 m/s) observed in the ionosphere. The ions were also cold, having ion temperatures around 150K. The combination of these factors meant that the ions appeared as a highly-directed supersonic beam in the spacecraft frame. This means the ions appear at kinetic energies associated with the spacecraft velocity and the ion mass, therefore the measured energy spectra (eV/q) can be converted to mass spectra (u/q).&#160;Results and ConclusionsPositive ion masses between 170 and 310 u/q are examined with ion mass groups identified between 170 and 275 u/q containing between 14 and 21 heavy (carbon/nitrogen/oxygen) atoms4. These groups are the heaviest positive ion groups reported so far from the available in situ ion data at Titan.The ion group peaks are found to be consistent with masses associated with Polycyclic Aromatic Compounds, including Polycyclic Aromatic Hydrocarbon (PAH) and nitrogen-bearing polycyclic aromatic molecular ions. The ion group peak identifications are compared with previously proposed neutral PAHs5 and are found to be at similar masses, supporting a PAH interpretation. The spacing between the ion group peaks is also investigated, finding a spacing of 12 or 13 u/q indicating the addition of C or CH. Lastly, the occurrence of several ion groups is seen to vary across the five flybys studied, possibly relating to the varying solar radiation conditions observed across the flybys.The discovery of these groups will aid future atmospheric chemical models of Titan through identification of prominent heavy positive ions and further the understanding between the low mass ions and the high mass negative ions, as well as the process of aerosol formation in Titan's atmosphere.References1. Waite et al., The Process of Tholin Formation in Titan&#8217;s Upper Atmosphere, Sci., 2007, doi:10.1126/science.11397272. Crary et al., Heavy ions, temperatures and winds in Titan's ionosphere: Combined Cassini CAPS and INMS observations, P&SS, 2009, doi:10.1016/j.pss.2009.09.006.3. Young et al., Cassini Plasma Spectrometer Investigation. Space Sci. Rev., 2004, doi:10.1007/s11214-004-1406-44. Haythornthwaite et al., Heavy Positive Ion Groups in Titan's Ionosphere from Cassini Plasma Spectrometer IBS Observations, eprint arXiv:2009.087495. L&#243;pez-Puertas et al., Large Abundances of Polycyclic Aromatic Hydrocarbons in Titan's Upper Atmosphere, ApJ, 2013, doi:10.1088/0004-637X/770/2/132

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Specimen Preparation of Near Surface Ion Irradiated Samples

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100117820 ◽

1985 ◽

Vol 43 ◽

pp. 170-171

Author(s):

K. F. Russell ◽

L. L. Horton

Keyword(s):

Radiation Damage ◽

Heavy Ions ◽

Target Material ◽

Metal Alloys ◽

Specimen Surface ◽

Specimen Preparation ◽

Particle Accelerators ◽

Near Surface ◽

Graaff Accelerator ◽

Van De Graaff

Beams of heavy ions from particle accelerators are used to produce radiation damage in metal alloys. The damaged layer extends several microns below the surface of the specimen with the maximum damage and depth dependent upon the energy of the ions, type of ions, and target material. Using 4 MeV heavy ions from a Van de Graaff accelerator causes peak damage approximately 1 μm below the specimen surface. To study this area, it is necessary to remove a thickness of approximately 1 μm of damaged metal from the surface (referred to as “sectioning“) and to electropolish this region to electron transparency from the unirradiated surface (referred to as “backthinning“). We have developed electropolishing techniques to obtain electron transparent regions at any depth below the surface of a standard TEM disk. These techniques may be applied wherever TEM information is needed at a specific subsurface position.

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