Collinear Laser Spectroscopy at ISAC

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Collinear Laser Spectroscopy at ISAC

• ISAC Seminar
• May 2005
• Thomas Cocolios
• McGill University

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Outline

• Nucleus properties
• Collinear Laser Spectroscopy
• Interest in the Lanthanides
• Experiment specifics

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Hyperfine Structure
m
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Isotope Shit
Isotope 1
Isotope 2
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Collinear Laser Spectroscopy
Laser beam
Accelerated beam (several tens of keV)
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Doppler Compression
For DE 3 eV n 18578.8 cm-1
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Interest in Lanthanum

• Models predict a change in deformation at
  low neutron number, observable with ltr2gt.
• Study of Lanthanum has been limited to long
  lived isotopes so far.

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Studied Transition
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Observed Spectrum
Microwave OLIS Source providing up to 2nA at the
detection region At the biggest peak, the signal
goes up to 9000 600 8400Hz which gives
4.2Hz/pA Background 600Hz gt Noise
25Hz
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Background
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Prediction with RIB

• Amongst the isobars, about 1pA is La. An estimate
  of the signal then is 4 Hz
• Signal-to-noise is then 1-to-5 over one second
  and does not permit peak identification
• Signal-to-noise increases as the square-root of
  the time gt it takes 10 times better
  signal-to-noise (2-to-1 ratio) for proper
  identification. For a scan of 500 channels, it
  then takes 500102 50000s 14 hours
• TOO LONG !!

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Improvements

• Reducing Laser induced backgrounds by knife-edged
  apertures, widen apertures, blacken plates.
• Laser Scattered Light ? Hz.mW-1 gt 33 Hz
• Shielding the activity at the source to bring
  that share of the background to 0 Hz.

TOTAL background 64 Hz Noise 8 Hz Scan
8000s 2 hrs 15 min
TOTAL background 140 Hz Noise 12 Hz Scan
18000s 5 hrs
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Conclusion

• Unknown metastable population from surface source
  limits prediction
• Long acquisition requires laser and energy
  stability
• At least one last offline test before going for
  radioactive beam