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Mass Spectrometry

2012 Student Practice in JINR Fields of Research 1.oct.2012. Mass Spectrometry. Brief introduction (part1). I. Sivacek flerovlab.jinr.ru. Mass spectrometer. Ion source – analyzing magnet – detector (basic setup) Isotope identification Molecule identification

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Mass Spectrometry

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  1. 2012 Student Practice in JINR Fields of Research 1.oct.2012 Mass Spectrometry Brief introduction (part1) I. Sivacek flerovlab.jinr.ru

  2. Mass spectrometer • Ion source – analyzing magnet – detector (basic setup) • Isotope identification • Molecule identification • Chromatography • Microscopes • AMS • RIBsand many more…

  3. Charged particles and ions • Neutral atoms (p = e) • Charged atoms = ions (p ≠ e) • Neutral particles (f.e. neutron) • Charged particles (f.e. proton, electron…) • Charged = with electric charge

  4. How to create ion ? • E=hν (a) • If energy is given to neutral atom • Excitation, de-excitation (a) • Ionization (b) • Thermal ionization • Chemical ionization • ECR (uniform magnetic field; plasma; 2,45 GHz microwave power) Incident radiation (Or other kind of energy) (b) -

  5. Ions with kinetic energy • Interactions of charged particles and ions: • ionization • excitation • elastic scattering • bremmstrahlung

  6. Ion ionization • Bethe formula for ion energy loss • α ~ 1 MeV/cm (1 atm = 101 kPa = 760 Torr) • Bragg curve – stopping power => Vacuum is needed ! Electron density of target Ion charge Ion velocity

  7. Electric and magnetic field • Electric field: (accelerates) • Magnetic field E = |U2 – U1| Lorentz Law (1)

  8. Mass separation in magnetic field • Mass-over-charge ratio radius r Generally at E-M field =1 mag. field: E=0; |Fm| = qvB.sinα => r = (m/q)(v/B) (2)

  9. Cyclotron Magnetic field • Lorentz force in magnetic field keeps orbits • Electrical field between duants accelerates ions • Cyclotron frequency (particle velocity does not depend on time of flight thru magnetic field)* Beamline * (2) => r = const. v Duants (electrodes with HF oscillating electric field)

  10. Detection of particles • Generally, all types of detector can be used • Spectroscopic detectors • Semiconductor • Scintillators • Gas detectors • Time-of-flight (and many more) • Counters (quantitative analysis) • Gas detectors • Pick-ups • Faraday cups (and many many more…) Warning: Since high ionization ability of charged ions, proper choice of detector strongly depends on application and characteristics of detected beam !!

  11. Mass resolution • Ability of device to resolve between two masses m and m+Δm • Defined as (by FWHM) Resolution on ion source-magnet-detector array Radius of ion in magnetic field Dispersion on ion source Dispersion after magnetic sector D [mm/%p] D = Δx/ΔBρ = Δx/Δp strip number Strip Translation on focal plane Ion impulse

  12. End of part 1 Now you are free for a while

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