Laser Spectroscopy on Bunched Radioactive Ion Beams Jon Billowes University of Manchester Balkan School on Nuclear Physics, Bodrum 2004
Lecture 1. 1.1 Nuclear moments 1.2 Hyperfine interaction in free atoms 1.3 Lasers and laser spectroscopy 1.4 Collinear-beams laser spectroscopy Lecture 2. 2.1 Ion beam cooling and bunching 2.2 Experiments with bunched beams 2.3 Laser ionization techniques Balkan School on Nuclear Physics, 2004 www.man.ac.uk/dalton/files
Summary of Isotope Shift and Hyperfine Structure Isotope shift of atomic transition ppm shift Analysis yields the change in nuclear mean square charge radius Hyperfine structure of atomic transition 176 Hf 178 Hf Nuclear size, static and dynamic deformations (Isotope shift found using centroids of hyperfine multiplet) Nuclear spin I Magnetic moment µ Quadrupole moment Q s 177 Hf
2.1 Ion beam cooling and bunching Fast ion beam Ion beam cooler Light collection region (Laser resonance fluorescence) +40 kv Reduces energy-spread of ion beam Ions accelerated while still in low-pressure helium acquire a large energy spread the collinear-beams Improves emittance method of loses ion both beamresolution and sensitivity. Trap and accumulates ions typically for 300 ms Solution: Releases an ions beam in a 15 cooler µs bunch
The JYFL cooler/buncher
Principle of RFQ trap Time-averaged force towards central axis Damping of motion provided by lowpressure helium gas at room temperature
Bunching ions in the RFQ cooler
Ion beam cooler Light collection region (Laser resonance fluorescence) Reduces energy-spread of ion beam +40 kv Improves emittance of ion beam Trap and accumulates ions typically for 300 ms Releases ions in a 15 µs bunch
Background reduction by signal gating
Sensitivity gains using the RFQ ion-cooler 200 BEFORE 8000 ions/sec 100 Laser frequency 5.3 hours Photons from laser-excitation of radioactive 88 Zr 30 AFTER 2000 ions/sec 48 minutes 0
2.2 Experiments with bunched beams 1. Zr isotopes shape changes near N=50 shell 2. Ce isotopes shape transition at N=60 3. Neutron-deficient Ti proton skins? 4. High spin isomers effect of pairing reduction?
Fission fragment spectroscopy Proton number Zr V. Rubchenya Neutron number Fission product yields at IGISOL (25 MeV p + 238 U)
Charge radii of Zr isotopes mean square charge radius 40 Zr Deformed nucleus Spherical nucleus Spherical droplet model Myers & Schmidt, Nucl. Phys. A410 (1983) 61.
Radii predictions for 40 Zr from B(E2) values (Very similar to 38 Sr behaviour) 40Zr Shaded areas: only B(E2) to the first 2 + state used. Should also include higher states and B(E3) strenghts.
Isotope shifts of neutron-rich Ce Mean square charge radii 331 nm (Ce + )
Brix-Kopfermann plot (differential changes in mean square charge radii)
Light Ti isotopes Produced by 45 Sc (p, xn) 46-x Ti Is 44 Ti an α-cluster nucleus? 40 Ca or 40 Ca 44 Ti Off-set centre of mass In fact: almost no difference in predicted rms radius! 42 Ti Does 42 Ti have a proton skin? (the laser measurement would be very sensitive to this) T 1/2 = 200 ms Neutron number
Comparison with RMF (G. A. Lalazissis et al., Nucl. Phys. A628 (1998) 221 Comparison with neighbouring chains
The K=8 isomers in 130 Ba and 176 Yb Structure of 2-neutron 8 - state in 176 Yb
The 176 Yb K=8 isomer Production: (d,pn) at 13 MeV, 5.5 µa Flux: 200 isomers/sec (total flux at A=176: 8,400 ions/sec)
8-23/2-16 +
Calculation by Bordeaux Group (Quentin, Pillet, Libert) Without pairing effects, Isomer shift = +0.092 fm 2 Including pairing Isomer shift = -0.086 fm 2 (Experiment: -0.076(12) fm 2 )
Explaining 178 Hf (16 + ) isomer shift Similar features now found in 4 isomers: smaller radius than ground state, but not due to reduction in deformation. Effect greatest for 4qp state. Effect for 2qp isomer is about twice the normal odd-even staggering (a 1qp effect?).
New development: Laser ion source FURIOS (using laser resonance ionization) Powerful pulsed lasers can be tuned to ionize neutral atoms of a selected element with high efficiency 2-laser scheme 3-laser scheme Applications: Laser ion sources beams selected by mass and atomic number Ultra-high sensitivity laser spectroscopy collinear beams RIS
The CRIS method 5 µs Atom bunch 50 Hz delivery rate, synchronized with laser pulse All atoms from the ion source have a chance to be ionized Resonance located by ion counting (not photon counting) Doppler-broadening free 10 ns Off-line tests with 27 Al 50 Hz repetition rate lasers Ionization limit 532 nm 308 nm
Collinear resonance ionization spectroscopy Charge exchange cell Ionization region
Laser fluorescence spectra 27 Al 1.5 GHz 308.2 nm Detection efficiency: 309.3 nm 1 photon detected per 50,000 atoms in beam 309.2 nm
Comparison with low-flux bunched beams Photon counting (12 minutes) Ion counting (4 minutes) Sensitivity: 1 resonance ion per 30 atoms within 1 µs time window (compared with 1 photon per 50,000 atoms) 1.5 GHz
Laser transportation and atom beam overlap Cyclotron beam CVL Dye 1 Laser beams Dye 2 Gas inlet ~ 10cm Ion beam to experiments Ti:Sa 1 Ti:Sa 2 Ion guide Mass separator Ti:Sa 3 RF multipole Laser system Nd:YAG
(Fast Universal Resonant laser IOn Source) Ti:Sapphir e lasers Nd:YAG pump laser Decay spectroscopy Penning Trap Mass spectroscopy Collinear laser spectroscopy Ion Guide RFQ cooler
Accessibility of elements using lasers Elements studied with dye laser RIS V. Fedoseyev, ISAC-TRIUMF 1 H Dye laser RIS possible LIS Workshop, 2000 2 He 3 Li 4 Be Ti:Sapphire laser RIS demonstrated 5 B 6 C 7 N 8 O 9 F 10 Ne Ti:Sapphire laser RIS possible 11 Na 12 Mg 13 Al 14 SI 15 P 16 S 17 Cl 18 Ar 19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 31 Ga 32 Ge 33 As 34 Se 35 Br 36 Kr 37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 49 In 50 Sn 51 Sb 52 Te 53 I 54 Xe 55 Cs 56 Ba 57 La 72 Hf 73 Ta 74 W 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84 Po 85 At 86 Rn 87 Fr 88 Ra 89 Ac Rf 104 105Ha 106 107 108 109 110 111 112 113 58 Ce 95 Pr 60 Nd 61 Pm 62 Sm 63 Eu 64 Gd 65 Tb 66 Dy 67 Ho 68 Er 69 Tm 70 Yb 71 Lu 90 Th 91 Pa 92 U 93 Np 94 Pu 95 Am 96 Cm 97 Bk 98 Fc 99 Es 100 Fm 101 Md 102 No 103 Lr NIPNET meeting, Saariselka,, April 2004
End of Lecture 2