Laser spectroscopy and resonant laser ionization atomic tools to probe the nuclear landscape. Iain Moore University of Jyväskylä, Finland

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1 Laser spectroscopy and resonant laser ionization atomic tools to probe the nuclear landscape Iain Moore University of Jyväskylä, Finland Nordic Conference on Nuclear Physics 2011

2 Outline Introduction to laser spectroscopy Medium-heavy nuclei at JYFL and ISOLDE In-source resonance ionization spectroscopy Towards the future

3 A nuclear fingerprint in the atomic spectrum 20 µev Model Dependent (inferred) Model Independent (measured) Y + Dynamic / static deformations Sizes Quadrupole moments Isotope Shift δ<r 2 > Isomer Shift δ<r 2 > Single / few particle configurations Spins Magnetic moments Hyperfine Splitting

4 Laser spectroscopy measurements (almost) to date After 1995 Before 1995 Z B. Cheal and K.T. Flanagan, J. Phys. G 37 (2010) N J. Billowes and P. Campbell, J. Phys. G 21 (1995) 707

5 The workhorse Collinear Laser Spectroscopy Ion Source Charge exchange CW tunable laser Separator electrostatic acceleration (30-60 kv) Applied Doppler tuning voltage PMT 178g,m Hf (isomer 8 - spin) ν 0 ν

6 JYFL and ISOLDE: complementary facilities Thick target (45 g/cm 2 UC x ) Protons (1.4 GeV) ISCOOL IGISOL Thin foil targets (mg/cm 2 ) Fast extraction (~1 ms) Chemically non-selective Ion guide COLLAPS

7 RF cooler-buncher innovations in detection Ungated Charge exchange Background due to scattered light Photon counts 76 Ga Gated (64-70 μs) TOF (50 ms acc.) Applied Doppler tuning voltage End plate potential PMT Accumulate Reacceleration potential Release z Background suppression 50 ms/6 μs = ~10 4

8 Evolution of nuclear shells far from stability ``Tensor force attractive between L+1/2 and L-1/2 orbitals 1g 9/2 N=50 5/2 Otsuka (PRL 95 (2005) ) protons neutrons Spin inversion (also seen between 73 Cu and 75 Cu) K.T. Flanagan et al., PRL 103 (2009) Not quantitatively predicted by any theory (collective state) N=40 3/2 3/2 2 3/2 1/2 3/2 3/2 3/2 Emptying of p3/2 B. Cheal et al., PRL 104 (2010)

9 Discovery potential of laser spectroscopy Isomeric state discovered in 80 Ga 4p 2 P 3/2 5s 2 S 1/2 (Dipole transition: F = 0, +/- 1) I=3 At most 6 peaks expected. Not seen in high precision mass measurements. J. Hakala et al., PRL 101 (2008) B. Cheal et al., PRC 82 (2010) (R) Isomeric states may be missed due to Τ 1/2 or mass/energy resolution

10 But what if the atomic/ionic spin is unfavourable? Optical manipulation of ionic/atomic states J=0 J=1 gives μ, Q, δ<r 2 > but not I Access to more accessible/efficient transitions New elements to study tunable pump laser

11 Completing the study of deformation at N=60 δ<r 2 > 50,N (fm 2 ) 5 Kr Rb Sr 4 Y Zr 3 Nb ** Mo * Z = 36 to N * F.C. Charwood et al., Phys. Lett. B 674 (2009) 23 ** B. Cheal et al., Phys. Rev. Lett. 102 (2009) N

12 Charge radii and masses: complementary tools F.C. Charwood et al., Phys. Lett. B 690 (2010) 346 Unlike the Z~40 region, the Mn charge radii do not follow the nuclear binding trends, rather they closely reflect the behaviour in level systematics and nuclear shell model structure. G. Audi et al., Nucl. Phys. A 729 (2003) 337

13 Resonance ionization spectroscopy (RIS) non-resonant ionization excitation of auto-ionizing states ionization of Rydberg-states ~6 ev (5-9 ev) ionization potential higher excited states σ Ι ~ cm 2 σ Ι ~ cm 2 extraction field or collisional ionization energy first excited state E 1 Z Laser σ R ~ cm 2 ground state 0 ev E 0 Mass Separator Efficiency Selectivity N

14 RIS in-source vs. collinear laser spectroscopy RIS is sensitive and selective Low lifetimes, low yields X Poor resolution Complementary method Post-accelerated isomeric beams Cu β β 1 + (g.s.) Counts Collinear data (ISOLDE 2008) Cu I. Stefanescu et al., PRL 98 (2007) P. Vingerhoets Relative et al., Frequency PRC 82 (2010) (MHz)

15 Early onset of deformation in Po isotopes Mid-shell (N=104) Shell closure (N=126) δ<r 2 > (fm 2 )[arb. separation] Spherical FRDM Τ 1/2 = 33 ms 0.3 ions s -1 T. Cocolios et al., PRL 106 (2011)

16 Resonant laser ionization in a gas cell Laser beams Longitudinal Ar/He from gas purifier Dual Chamber design 500 mbar The aim: (by separating stopping and laser ionization chambers) Beam from Cyclotron Laser Ionization chamber Target Ion collector Ionization chamber Ion Collector Filament Increasing laser ionization efficiency at high cyclotron beam currents Increasing selectivity (collection of non-neutral ions) >2200 RIB, stable Ni Laser beams Transverse SPIG Exit hole Ø mm In-source spectroscopy of neutron deficient Cu isotopes (T. Cocolios et al., PRL 103 (2009) ) Investigate possibility of performing similar measurements near N=Z line around A=100 Yu. Kudryavtsev et al., NIM B 267 (2009) 2908

17 In-cell laser spectroscopy on Ag 109 Ag N=50 92 Mo( 14 N,2pxn) 103-x Ag nat Zn( 36 Ar,pxn) * Ag 101 Ag 102 Ag 99 Ag 100 Ag 97 Ag 98 Ag Preliminary results missing comparison with shell model calculations Courtesy of Iain Darby

18 Development of a novel hot cavity at JYFL Count rate (ions/s) Step 3: non-resonant 511 nm P sat = 3.3(W) Power (W) Count rate (ions/s) Step 2: nm P sat = 10(6) mw Power (mw) Count rate (ions/s) Step 1: nm P sat = 1.7(4) mw M. Reponen et al., Eur. Phys. J. A 42 (2009) Power (mw)

19 Towards the study of the exotic 94 Ag m (21 + ) Not directly measured with JYFLTRAP! β + daughter 2p daughter N=Z=47 Exotic decay modes: βγ, βp and β2p, direct p and 2p 2p decay explained by large prolate deformation? I. Mukha et al., Nature 439 (2006) 298 I. Mukha et al., PRL 95 (2005) J. Cerny et al., PRL 103 (2009) Excitation energies of 21 + isomer based on 1p and 2p decay differ by 1400(545) kev. A. Kankainen et al., PRL 101 (2008)

20 Towards laser spectroscopy in a gas jet Simulation of the spectral linewidth in copper. Doppler broadening ( K) Pressure broadening Expanding gas jet is cold and has low pressure (300 K) Resolution in gas jet limited by laser bandwidth T. Sonoda et al., NIMB 267 (2009) 2918

21 Laser Ion Source (Trap) Ion repeller RFQ segments Electron repeller 10 mm Switchable electrodes Hot cavity or gas cell Atoms Buffer Gas Laser Beams Ions End plate U DC Accumulate Laser ions Surface ions Electrons Release K. Blaum et al., NIMB 204 (2003) 331; I.D. Moore et al., AIP Conference Proceedings 831 (2006) 511 Z

22 Gas jet studies at JYFL 0.17 mbar 2.3 mbar P He = 56 mbar 0.59 mbar 5.6 mbar M. Reponen, I.D. Moore et al., NIMA 635 (2011) 24

23 Laser spectroscopy of Ni: gas cell vs. gas jet Reference cell FWHM= ~ 3 GHz Gas cell He 200 mbar FWHM= ~ 6 GHz Gas jet 7 GHz FWHM= ~ 4 GHz

24 IGISOL-4 (Autumn 2011 / Spring 2012) K=30 MeV K=130 MeV Off-line source: (discharge, carbon cluster ) Laser ionization & gas jet LIST Decay spectroscopy Mass spectrometry & post-trap spectroscopy Collinear laser spectroscopy

25 Looking towards the future Towards Superheavy Elements A variety of techniques are needed to probe the regions of interest. Further away from Stability Clusters and Halos Refractory Elements around Shell Closures TRIUMF ( 74 Rb recent measurement!) MSU (Becola) LaSpec at FAIR (prototype at TRIGA) Lumiere at DESIR, SPIRAL2

26 Manchester, Birmingham, JYFL laser collaboration ISOLDE (COLLAPS) Leuven (LISOL team) Thank you