Solid Sample-SIMS on Biomolecules with Fast Ion Beams from the Uppsala EN-Tandem Accelerator
Secondary Ion Mass Spectrometry (SIMS) on bioorganic solids was first performed by R.D. MACFARLANE and coworkers  in 1974 using fission fragments from a Cf-252 source as primary particles. Fission fragments are fast particles i.e. with a velocity larger than the Bohr velocity (v0=2.0.108 cm/s) interacting mainly with the electrons in a medium. In most SIMS-studies performed so far slow particles are used as primaries. Slow particles interact primarily via elastic collisions with the atoms in a solid. Macfarlane called the mass spectrometric method based on the use of fission fragments from Cf-252 and time-of-flight (TOF) analysis, 252CfPlasma Desorption Mass Spectrometry (PDMS), and proposed a new formation process different from that assumed for the secondary ion formation by keV-ions. 1976 BENNINGHOVEN et al. applied static SIMS to bioorganic solids. Very similar spectra were found and therefore the same ion formation process for PDMS and SIMS was postulated . A major contribution to the field was made in 1981 by BARBER et.al.  with the introduction of slow ion-liquid sample-SIMS with a magnetic sector instrument (FAB).A1ready at an early stage Macfarlane et.al. showed that fission fragments were very effective to desorb and ionize large and labile biomolecules  and a joint study by the Texas and Uppsala groups showed that the fast primaries are more efficient than slow primaries and more so the larger the molecule is .
KeywordsFission Fragment Thickness Dependence Slow Particle Initial Velocity Distribution Plasma Desorption Mass Spectrometry
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