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