Radioactive ion beam facilities How does they work ? 2012 Student Practice in JINR Fields of Research 9.oct.2012 I. Sivacekflerovlab.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 efficiency ξ = ξ Diff ・ ξ Ion ・ ξ Sep I 2 = σ N t Φ ξ EFFICIENCY IS CRUCIAL Proper choice of equipment for each experiment is needed !

Secondary beams preparation In-flight ( 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 48 Ca (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 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 W i > 7 eV) – Energetic electrons hit neutral atom in el. field Thermoionization/surface ionizations – X + (W i 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 – 2 nd 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