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Gas jet laser ionization: developments towards selective RIB production and studies of exotic atomsIain MooreJYFL, FinlandI.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013

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General introduction to RIB production Probing the gas jet

In-jet laser ionization

OutlookOutline of talk

I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013

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General methods of RIB production (I)

I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013High-energyprimary beamRadioactive atomsLow-energyion beamMass selectionISOL methodkVHigh yield but difficult for refractoryelements, chemically active elements.Z and T1/2 dependenceBorn in 1951, Niels Bohr InstituteISOL facilities: TRIUMF, GANIL, ALTO,ISOLDE (Wed. talks) SPES (Thurs.)ISOL primary beam often ~100 MeV/u, in-flight beam ~1 GeV/u. Isotope separation via em separator.Thick target ISOL method.3

I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013

High-energy primary beamProjectile fragmentsIsotope selectionMedium-energyion beamIn-flight method

General methods of RIB production (II)Very fast separation, access to s half-livesand beams of ALL elements.Often poor beam quality.Precision experiments at low-energy notdirectly accessible.First in-flight separator, Oak Ridge (1958)

The ion guide / gas catcher method

I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013

an ISOL system for ALL elements, fast extractionProjectile sourceThin targetmass separatorNeutralizationLaser re-ionizationZ selectivity;Laser Ion GuideIon survivalIGISOL

Fast beamsPurification in-flightelectrical fields``The best of both worldsUniversal, but for IGISOL we have a lot of isobaric contamination.Low yields due to thin target.5~6 eV(5-9 eV)ground statefirst excited statehigher excited statesionization potentialE1energy0 eVE0non-resonant ionizationexcitation ofauto-ionizing statesionization ofRydberg-statesextractionfield orcollisionalionizationPrinciples of laser ionizationsR ~ 10-12 cm2sI ~ 10-17 cm2sI ~ 10-15 cm2Efficiency Selectivity

NZ

I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 20136General requirement is that all resonant steps should be saturated. Bottle neck is then the ionization step. Very important to increase the cross section of ionization. Cross section for excitation of AI state is related to the transition rate of state and hence linewidths are typically 1-2 oom larger than bound state resonances. Rydberg levels are atomic states of high n close to IP. Ionization occurs via E fields, IR radiation or collisions. The laser provides the element (Z) selectivity, the magnet provides A selectivity and thus increases the selectivity. Selectivity in RIS defined as the probability of exciting the thing you want (eg isotope) to the often far more abundant things unwanted. Typical laser selectivities can be ~1000 per step.

I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013

repetition rate: ~10 kHz tuning range: - fundamental 700 - 1000 nm - frequency doubled 350 - 500 nm - frequency tripled 240 330 nm - frequency quad. 205 - 250 nm laser linewidth: >5 GHz (broad) 15 GHz to 1.5 WMark 2 (Nagoya, Japan)Mark 3 (JYFL, Finland) - cw Matisse laser ordered with pump - ring cavity being developed - TEM locking electronics bought27Al

Towards the future

I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013

In-gas-cell and in-gas-jet laser ionization at S3 facility, SPIRAL-2, GANILContinuation of jet studies with laser ionization (nozzles etc)Spectroscopy of exotic nuclei in the jet with injection-locked lasers

Thank you

Mikael Reponen, Volker Sonnenschein, Ilkka PohjalainenTobias Kron, Klaus Wendt Yuri KudryavtsevHideki TomitaYu. Kudryavtsev et al., NIM B 267 (2009) 2908Dual-chamber gas cell commissioning (2012)

Laser beamsLongitudinalSPIGAr/He from gas purifierIon CollectorIonizationchamber

Beam from CyclotronTargetExit hole 0.5 1 mm17%11%2%M. Reponen, PhD thesis, JYFL (2012)

36Ar(natZn,pxn)101-97Ag

36Ar beam intensity (pA)223Ra -recoil sourceefficiencies33

FWHM= ~ 3 GHzFWHM= ~ 6 GHzFWHM= ~ 4 GHzHe 200 mbarGas cellGas jetReference cell 7 GHzLaser spectroscopy of Ni: gas cell vs. gas jet

No sensitivity to nuclearstructure however

Gas cellT. Sonoda et al., NIMB 267 (2009) 2918

34Ni scan in He buffer gas using LIST longitudinal. SPIG DC = 20 V. Resolution dominated by laser bandwidth. 7 GHz blue Doppler shift in gas jet correlates to 1660 m/s gas jet velocity.Not possible to extract nuclear information due to the limited contribution to the isotope shift of the nuclear effects, combined with the low resolution of the pulsed laser system.