Radioactive ion beam facilities How does they work ? 2012 Student Practice in JINR Fields of Research 9.oct.2012 I. Sivacek flerovlab.jinr.ru
Feb 23, 2016
Radioactive ion beam facilities
How does they work ?
2012 Student Practice in JINR Fields of Research 9.oct.2012
I. Sivacek flerovlab.jinr.ru
How to prepare secondary beams ?
Efficiency and selectivity
• ISOL systems has advantage in better selectivity
• Fragment separators have more intensive secondary beams
• Every process has it’s own efficiencyξ = ξDiff ・ ξIon ・ ξSep
I2 = σ Nt Φ ξ
EFFICIENCY IS CRUCIALProper choice of equipment for each experiment is needed !
Secondary beams preparation
• In-flight (10 - 1000 MeV/u, thin target)– Projectile fragmentation (scattering to small
angles, few nucleons lost)• Heavy projectile on light target -> n-rich, mid A• Light projectile on heavy target -> n-def., low A
– Fusion• Cold – 1n channel (GSI Darmstadt)• Hot – 3n, 4n with double-magic 48Ca (JINR Dubna)
• Isotopes with τ ~ μs• Significant emittance
Secondary beams preparation
• ISOL (any target, any projectile)– Fragmentation (protons, heavy ions)– Fission (neutrons, heavy ions)• Variety of mid-A isotopes (light and heavy fragment)
– Spallation (protons)• n-deficient, close to β-stability line
– Fusion (heavy ions)• n-def,. far from β-stability, ~ 5 MeV/u projectiles, selective
• τ > ms• High selectivity, better emittance, up to 60 keV
Thermalization of reaction products
• Thick hot target (ISOLDE) *converter – high Z (W, Ta)
• Hot catcher (MASHA)– Fast release, high diffusion and effusion efficiency (low
effusion materials Ti, V, Zr, Nb, Mo, Hf, Ta, W – ideal for construction materials – Ta heater at MASHA catcher)
• Gas catcher (Gas cell for thermalization of reaction products)
*IGISOL
Target-catcher system is usually not selective
&
MASHA hot catcher
Heavy ionbeam
Target
Hot catcher(graphite)
1TO12, 114
ECR
Heater
Separating foil
4-sector diaphragm for beam diagnostic
2 μm Ti foil
Ion source• IGISOL (ions are evacuated in 1+ or 2+ state)
– Charge state: evacuation time, He purity, e - ion density in gas cell, chemical properties
• Impact ionization (elements Wi > 7 eV)
– Energetic electrons hit neutral atom in el. field• Thermoionization/surface ionizations– X+ (Wi < 7 eV); X- (EA > 1,5 eV) *catcher heater materials
• Laser resonance ionization• Electron cyclotron resonance
Not very selective
Very fast method
Very selective (alkali metals, halogens)
VERY selective
Not very selective, great efficiency
Laser ionization
• Isobaricaly and isomericaly pure secondary beams
• Pulse laser – tunable wavelength
• Competitive de-excitation
• Non resonant high power laser ionization for highly charged ion beams
Electron cyclotron resonance
• Plasma including all electrons and ions• Magnetic field keeps plasma volume• Resonance frequency 2πf = ω = e.B/m for electron
mass m, elementary charge e and magnetic field strength B = 0,0875 T
• 2,45 GHz microwave power – electrons gain energy in resonance
• Impact ionization• C, N, O: ~ 50%; Xe: ~ 90% (only volatile elements)
ECR ion source scheme
Working gas (He)Reaction products
1+ reaction products,1+ working gas
40 kV acceleration
Mass separation• Fragment separators (in-flight)– Light fragments q = Z– Heavy fragments q ≤ Z -> degraders
• Mass separators (ISOL)– Dipole magnet (magnets, or combination with TOF)– The higher angle – the better resolution
Ion optics• Dipole magnets – mass analysis
• Quadrupole lenses – focusation– linear corrections of beam-shape– dispersion changes– linear or 3D ion traps (*mass analysis)
– HF quadrupoles - beam cooling• Sextupoles– 2nd order (nonlinear) corrections of beam spot– wobbler
Detection systems
• Position-sensitive spectrometric “stop detectors”• Time-of-flight systems• Faraday cups for beam diagnostic
• Post acceleration– Linac– Tandem accelerators– Cyclotrones (also used as very precise mass separators)
QUESTIONS !Now is the right time for