Opportunities with collinear laser spectroscopy at DESIR:

Size: px

Start display at page:

Download "Opportunities with collinear laser spectroscopy at DESIR:"

John Rose
5 years ago
Views:

1 Opportunities with collinear laser spectroscopy at DESIR: the LUMIERE facility GOALS of LUMIERE experiments: Gerda Neyens, K.U. Leuven, Belgium (1) measure ground state properties of exotic isotopes: (see Campbell, Cheal, Flanagan, Charlwood, Furukawa, Cocolios) * nuclear spin * magnetic moment + sign deduce parity of the g.s. * quadrupole moment + sign deduce deformation / core polarization * charge radius get information on single particle and collective behavior and their interplay (2) measure β-asymmetry of a specific β-decay branch: (see T. Shimoda talk) determine spins of levels in daughter isotope

2 Opportunities with collinear laser spectroscopy at DESIR: the LUMIERE facility LUMIERE: Laser Utilization for Measurement and Ionization of Exotic Radioactive Elements Methods based on ion (or atom) laser interactions: Colinear laser spectroscopy β-nmr spectroscopy on laser-polarized beams β-decay spectroscopy on laser-polarized beams

3 Colinear laser spectroscopy: measure the hyperfine structure (HFS) in a free atom/ion Fine structure: electron levels with spinj 3 2 S 1/2 F P 3/2 2 1 λ L = nm (3.82 ev) Hyperfine structure 0 2 E ~ A 1 Example: atomic levels and HFS of 67 Cu (nuclear g.s. spin I=3/2) I-J < F < I+J E ~ B B = e QV zz measure Q A= µb J IJ = gb J /J measure g Fluorescence photon counts relative frequency (MHz) Relative distances: spin dependent Need to resolve all HFS levels to be measure the spin High resolution needed ion velocity should be very well defined to reduce Doppler broadening of the resonances (< 0.01% error on beam velocity) use an accelerated ion beam = COLINEAR LASER SPECTROSCOPY

4 Colinear Laser Spectroscopy: resonant interaction between accelerated ion beam and a parallel laser beam ion beam from ISOL-target/gas cell : energy uncertainty ~ few/several ev error on energy remains constant during acceleration error on beam velocity decreases with increasing beam velocity: ΔE=const=δ( 1 / 2 mv 2 ) mvδv Narrow Doppler line width ~ 50 MHz can be achieved with beam of 60 kev

Ion beam Collinear Laser Spectroscopy with optical detection of the fluorescent decay on continuous ion beam Photon counters Need 10 6 ions/s Large photon background from laser beam!

5 Ion beam Collinear Laser Spectroscopy with optical detection of the fluorescent decay on continuous ion beam Photon counters Need 10 6 ions/s Large photon background from laser beam! Laser beam Change velocity of ion beam = Doppler tuning of ion beam Electrostatic lenses to scan ion beam energy from +10 kev to -10 kev to scan hyperfine structure levels: ν scan =ν laser γ(1+β) β U 1/2 Photon counts Example: 25 Mg measure fluorescent photon decay

6 Collinear Laser Spectroscopy with optical detection of the fluorescent decay on bunched beam IMPROVE DETECTION SENSITIVITY by 2 orders of magnitude by using a BUNCHED ion beam reduces photon background by factor 4000 = T/ T T = 25 µs pulse length T = 100 ms repetition rate Example: 72 Cu Need 10 4 ions/s 40 hours Limit without ion bunching Limit with ion bunching 2 hours Relative frequency (MHz)

7 Collinear Laser Spectroscopy with β-asymmetry detection on polarized nuclei Need 10 3 ions/s Ion beam Photon counters Magnet coil β-scintillators crystal Laser beam Doppler tuning Magnet coil β-scintillators Resonant optical pumping with circularly polarized laser light to polarize the atoms and nuclei m F2 m F1 Total atomic spin F gets polarized through pumping Nuclear spins are polarized! β asymmetry 31 Mg Detection of HFS via asymmetric nuclear β-decay after implantation in crystal Dopple tuning voltage

8 Collinear Laser Spectroscopy with ion detection or β/α-decay detection after resonant re-ionization (CRIS) Need ion/s Charge exchange cell: neutralize the ion beam atom beam See Kieran Flanagan Under development at ISOLDE Re-ionization region Pure ion beam: only resonantly ionized ion detection No background! Higher efficiency! AIS nm D 3/2 CONDITION: Ulta High Vacuum Deflection of ions towards ion detector Neutral background 327.4nm Cu atomic levels P 1/2 S 1/2 resonant re-ionisation of atom beam: apply two lasers at same time: - step one: resonant excitation (narrow band laser) (to scan hyperfine structure) - step two: ionization (broad band)

9 β-nmr spectroscopy on laser-polarized beams: High precision measurements of g-factor, Q-moment Need 10 3 ions/s Ion beam Photon counters Magnet coil β-scintillators crystal + rf-coil Laser beam Doppler tuning Magnet coil β-scintillators Set tuning voltage to select polarized beam Scan the rf-frequency ω rf g-factor β-asymmetry(%) 33 Mg, HFS I=3/2 hω L m=3/2 m=1/2 m=-1/2 m=-3/2 Zeeman splitting β-asymmetry(%) 33 Mg, NMR Relative laser frequency (MHz) RF-frequency (khz)

10 β-decay on laser-polarized beams: measure β-decay asymmetry parameter in β γ and β γ γ coincidence Need 100 ions/s See T. Shimoda Developed at Triumf Asymmetry parameter in allowed β-decay depends on the initial and final spin.

Possible layout for collinear spectroscopy at DESIR: anormal-vacuum line with 2 (or 3) end stations for optical detection, polarized beam experiments, a UHV beam with differential pumping for CRIS

11 Possible layout for collinear spectroscopy at DESIR: anormal-vacuum line with 2 (or 3) end stations for optical detection, polarized beam experiments, a UHV beam with differential pumping for CRIS CRIS beam line β-nmr set-up Polarization axis β-γasymmetry set-up Polarization axis Multi-purpose station (e.g. photon-ion coincidence detection) Polarization axis BUNCHED and COOLED beams from off-line ion source S2 or S3 beams based on collinear laser beam line at TRIUMF C.D.P. Levy et al. / Nuclear Physics A 746 (2004) 206c 209c

12 Day-1 experiments:shell structure far from stability ( 78 Ni, 132 Sn, 100 Sn) Extend existing laser spectroscopy studies beyond doubly-magic nuclei far from stability study the evolution of shell structure via spins, moments, radii, isomers, 249 Bk Am 249 Cf 255 Fm 254 Es With S3 beams from gas cell or laser ion source: neutron-deficient Sn, In, Cd nuclear structure around 100 Sn 82 Complementary to ion-source laser ionisation: higher resolution allows quadrupole moments and spin measurements In Cd Sn Gd Eu Sm Lu Hg Au Pt Hf Rn Po Tb Nd Ba Ra Fr Ir Yb Er Tm Ho Dy 227 Ac 232 Th Bi Pb Tl 248 Cm Pu Np U Sr Rb Cs Xe 32-40,46 Ar Ne ,45 Ti 6 He 6-11 Li Kr Na Be Cu Cu Ca K Zr Ag Ga With U-target + n-converter more neutron rich Sn, In, Cd nuclear structure below 132 Sn more neutron-rich in Cu, Ga, nuclear structure at 78 Ni and beyond N=50

13 Currently following groups showed interest: P. Campbell, K. Flanagan, J. Billowes, University of Manchester G.N., M. Bissell, K.U. Leuven F. Leblanc, IPN Orsay J.C. Thomas, GANIL D. Yordanov, ISOLDE-CERN G. Georgiev, CSNSM Orsay D.L. Balabanski, INRE, Sophia Please contact me if you are interested to help building (or financing) this set-up

14 Collinear Laser Spectroscopy with optical detection of the fluorescent decay Laser beam, Laser beam, fixed frequency Laser on fixed frequency Mass Mass separated separated ion ion beam beam E= 60 kev Retardation Electrostatic lenses zone: electrostatic lenses -10 kv +10 kv -10 kv +10 kv Electrostatic Electrostatic deflection deflection to scan ion beam energy Alkaline vapor Produce atom beam by charge exchange Charge exchange cell, heated ΔE=const=δ( 1 / 2 mv 2 ) mvδv ΔE=const=δ( 1 / 2 mv 2 ) mvδv Excitation / Observation Resonant excitation region of atoms Detect fluorescent decay Light guide with phototube Photo multiplier Photo multiplier

Laser Spectroscopy on Bunched Radioactive Ion Beams

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