The Collinear Resonance Ionization
Spectroscopy (CRIS) Programme at
ISOLDE
Jon Billowes for the CRIS Collaboration
Isotope shift of an atomic transition
ppm shift
Analysis of shift yields the change in nuclear mean square charge radius:
δ<r2> = <r2>A´
Isotope A
<r2>A
A´
volume
R
θ
R = R0 ( 1 + β2 Y2,0 (θ,φ))
z
deformation
Hyperfine Structure of atomic transition
Analysis of hyperfine
factors
Upper atomic
state
ν0
Nuclear spin I
Lower atomic
state
Magnetic moment µ
Quadrupole moment Qs
Experimental
spectrum
+
isotope shifts
ν0
For measurements on radioactive nuclei, need:
• High sensitivity
• High (sub-Doppler) resolution
δ<r2>
High sensitivity method developed at JYFL:
Bunched‐beam collinear laser spectroscopy
Gas‐filled linear RFQ trap
Ion beam
cooler
Laser beam
Light collection region
5 μs
(Laser resonance fluorescence)
+39.9 kV
40 kV
Reduces energy-spread of ion beam
Improves emittance of ion beam
+40 kV
Ion source
Trap and accumulates ions – typically for 300 ms
Photons only counted during the 5µs when ion Releases
ions in a 15 µs bunch
beam passes photomultiplier tube.
50 ms trapping = 104 reduction in background compared with a continuous ion beam
High sensitivity method developed at JYFL:
Bunched‐beam collinear laser spectroscopy
Gas‐filled linear RFQ trap
Ion beam
cooler
Laser beam
Light collection region
(Laser resonance fluorescence)
+39.9 kV
40 kV
Reduces energy-spread of ion beam
Improves emittance of ion beam
+40 kV
Ion source
Inefficient
of signal ions – typically for 300 ms
Trapdetection
and accumulates
All improved by
• Small
solid angle
Releases
ions in a 15 µs bunch counting ions
• Low quantum efficiency
instead of photons
• Background from laser light
Count ions instead:
Collinear Resonance Ionization Spectroscopy (CRIS)
Atom bunch
(mass selected, A)
(only a very small fraction of this
beam may be the nuclide of
interest)
Synchronized
laser pulses
Lasers only ionize
selected element, Z
Method can either measure laser resonances with high sensitivity and low background
Microchannel
plate
Ion Counter
6
Count ions instead:
Collinear Resonance Ionization Spectroscopy (CRIS)
Atom bunch
(mass selected, A)
(only a very small fraction of this
beam may be the nuclide of
interest)
Synchronized
laser pulses
Lasers only ionize
selected element, Z
Method can either measure laser resonances with high sensitivity and low background
Ion Counter
or
or
provide hyper‐pure samples of exotic nuclei, for low‐background nuclear spectroscopy
Catcher foil station &
Nuclear radiation detectors
(LANDS: Laser‐assisted nuclear decay spectroscopy) 7
ISOLDE ‐ CERN
1.4 GeV protons
from PSB
GPS target
radioactive
laboratory
HRS target
GPS
HRS
control
room
ISCOOL
CRIS laser line
ion beam
buncher
HIE ‐ ISOLDE extension
CRIS beam-line
Interaction region
(ultra high vacuum to
minimize collisional
ionization)
First measurements – francium isotopes
202-206,218,219,229,231Fr
179-185Tl
197,198,203,205,207,209,211,217At
191-210,216,218Po
182-189Pb
177-182Au
Neutron-rich Fr with CRIS:
Poster PS1-B031 (Ivan Budincevic)
N = 126
Neutron-deficient Fr isotopes at TRIUMF (high resolution):
A. Voss et al., Phys. Rev. Lett. 111, 122501 (2013)
30 Hz Nd:YAG (15 mJ)
synchronized with a pulse from a
RILIS frequency-doubled
10 kHz Ti:Sa (~50 mW)
Francium laser ionization scheme
K.T. Flanagan et al: proposal to INTC to
measure Fr isotopes, 2008
11
Example spectrum: 204Fr ground state and two isomers
Resolution: limited only by Ti:Sa pulsed laser to 1.5 GHz
Efficiency: 1% - including beam transport, neutralization, ionization and detection
Lowest yield:
202Fr
measured with production yield of ~100 atoms/sec
Neutron-deficient isotopes measured: Charge radii and magnetic moments for 202g,202m,
203,204g, 204m1, 204m2, 205, 206g, 206m1, 206m2,
LANDS – laser assisted nuclear
decay spectroscopy:
separation of 204Fr ground state and
two isomers
Alpha spectrum
K.M. Lynch et al., Phys. Rev. X 4 011055 (2014)
Laser resonance spectrum
Mean square charge radii of francium isotopes
The CRIS Collaboration
J. Billowes, T.E. Cocolios, K.T. Flanagan, T.J. Procter, A. Smith, I. Strashnov,
K.M. Lynch, S. Franchoo, V. Fedosseev, B. Marsh, G. Simpson, M. Bissell,
I. Budincevic, R.P. De Groote, S. De Schepper, R.F. Garcia Ruiz, H. Heylen, J.
Papuga, G. Neyens, H.H. Stroke, R.E. Rossel, S. Rothe, K. Wendt
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[email protected]