In-source laser spectroscopy of isotopes far from stability

(ISOLDE, CERN & IRIS, PNPI)Anatoly BarzakhPNPI

IS 511: Shape coexistence in the lightest Tl isotopes studied by laser spectroscopyIS 534: Beta-delayed fission, laser spectroscopy and shape-coexistence studies with radioactive 85At beamsIS 534 (addendum): Laser spectroscopy and shape-coexistence studies with radioactive 79Au beamsShape Coexistence in the Lead Region studied by laser resonance spectroscopy A collaboration of ~30 atomic and nuclear physicists12 institutionsISOLDEPreliminary results for At and Au isotopes!

Magnetic moments, hyperfine structure anomaly and mean squared charge radii of neutron deficient Tl isotopesIRIS

A,ZLaser Ion Source at ISOLDEIsotope shift (IS), hyperfine structure (HFS) measurements: The wavelength of the narrow-band laser is scanned across the chosen transition. The photoion current at the collector of the mass separator increases at the resonance. Detection of photoion current by measuring FC current, a//g or ToF spectra while scanning the frequency

Laser beamsMass separatorprotonstargetion sourceLaser Ion Source at IRISA substantial increase of the ionization efficiency can be achieved by decreasing of the inner diameter of the laser ion source tube with a corresponding focusing of the laser beam inside. At IRIS facility the laser spot as low as 1 mm in diameter can be provided due to a lens, placed in a distance of 2 m from the ion source

Detection: Windmill System at ISOLDEAnnular Si Sipure 50 keV beam from RILIS+ISOLDESetup: Si detectors from both sides of the C-foil

Large geometrical efficiency (up to 80%) 2 fold fission fragment coincidences ff-, -, -, etc coincidencesC-foils20 mg/cm2Si detectors50 keV beam from ISOLDESiAnnular SiffffaC-foilMINIBALL Ge clusterA. Andreyev et al., PRL 105, 252502 (2010)The WM technique requires waiting for the decay of the isotope (usually, -decay). Not practical for long-lived or stable isotopes (or for -decaying).

R. N. Wolf et al., Nucl. Instr. and Meth. A 686, 82-90 (2012), S. Kreim et al., INTC-P-299, IS 518 (2011)Multi-reflection time-of-flight mass separator (MR-ToF MS)

Detection: MR-ToF MS at ISOLDE

~1000 revolutions, ~35 ms, m/m ~ 105MR-ToF MS is not limited by decay scheme or long half-lives MR-ToF MS offers a way to separate background for direct single-ion detection using MCP (time scale: tens of ms).

Amplitudes of the components:Positions of the components:Ji=1/2Jf=1/2F1=I-1/2F2=I+1/2F1=I-1/2F2=I+1/2Number of components and their relative intensities give the possibility to determine nuclear spin I

IS

Green Beams 90 W @ 532 nmUV beam18 W @ 355 nm10kHz rep rate6 - 8 ns pulsesRILIS upgradeCVL to Nd:Yag

Laser ion source at ISOLDENd:YAG lasersDye lasersTi:Sa lasers3 Ti:Sa lasers:5 GHz linewidthUp to 5 W output power680 1030 nm (fund.)35 ns pulse lengthRILIS upgradeDye+Ti:Sa systemSince the two systems can be used either independently or in combination, there exists far greater flexibility for switching from one ionization scheme to another or rapidly changing the scanning step.

J. A. Bounds et al., Phys. Rev. C36, 2560 (1987); R. Menges et al., Z. Phys. A341 (1992) 475; H. A. Schuessler et al., Hfi 74 (1992) 13 IS/hfss were previously measured for 535 nm transition with reliably established F and M for 186-207Tl:

Electronic factor and mass shift for 277 nm transition (IRIS)

IRISIRIS & ISOLDEISOLDE186Tl, I=10, T1/2= 2.9 s195mTl, I=9/2, T1/2=3.6 s197mTl, I=9/2, T1/2=0.54 s

Hyperfine structures observed for 184Tl with different detection modesground state hfsIsomer selectivity for 184Tl (ISOLDE)

Shape coexistence and charge radii in Pb region2011: Tl isotopes: IS511 ISOLDE and IRIS (Gatchina)Pb ISOLDE, PRL98, 112502 (2007) H. De Witte et al.Po ISOLDE, T. Cocolios et al., PRL106, 052503 (2011)

Development and use of laser-ionized At beams at ISOLDE Determination of optical lines and efficient photoionization scheme. First measurement of the ionization potential of the element At

Beta delayed fission of 194,196At

Charge radii and electromagnetic moments measurement for At isotopes

AtPhotoionization scheme for the radioactive element At6p5, J=3/26p47s, J=3/26p48p(?), J=3/2 or 5/2In collaboration with TRIUMF-ISAC radioactive ion beam facility with the TRILIS laser ion source

Precise determination of the Ionization Potential for the radioactive element At

Isomer selectivity enable ISOLTRAP team to measure masses of 197g,198gAt.Nuclear spectroscopic information for pure g.s. was obtainedIS534: Isomer selectivity for 197,198At

IS534: Astatine HFS spectra1st step scanning is better for extraction2nd step scanning is better for hfs resolution (Q and determination). But to decipher these hfss one should know J for 58805 cm-1 level (5/2 or 3/2)

The number of peaks (4 rather than 3) unambiguously points to J=3/2 for 58805 cm-1 atomic state in AtIS534: Additional atomic spectroscopic information for Astatine58805 cm-1, J=3/2 or 5/2J=3/2J=3/2I=1/2

Isotope shift A,A:

for different transitions should lie on a straight line with a slope F1/ F2King plot for 216 nm and 795 nm lines in AtF216/F795(At)=-2.26(8)

compare with F256/F843(Po)=-2.241(7)for similar transitions in Po

IS534 October 2012:Charge radii of At isotopesWMWMMR-ToFFCAstatine seems to follow Polonium trend i.e. there is the same early onset of deformation after N=113. Data for lighter isotopes are necessary to verify this conclusion

October 2012:IS534 experiment at ISOLDE Au isotopesAre the light Au isotopes deformed?

What are the spins of ground and isomeric states?

Au ionization schemeAu hfs spectra

F1=0Jf=1/2F2=1F1=0F2=1Ji=1/2I=1/20>0 transition is forbidden!Only 3 rather than usual 4 peaks will be seen in the hfs spectra of isotopes with I=1/2 (for I=3/2 4 peaks)F2F1F1F2Is it possible to discriminate between I=1/2 and I=3/2 for Au isotopes by hfs spectra?

IS534: Hyperfine Structure Scans for 177,179Au 179Au (WM)179Au 3/2+ calculated179Au 1/2+ calculated177Au (WM)Number of peaks and their intensities ratiofix ground state spins of 177,179Au: I=1/2

Why is 1/2+1/2+ 181Tl177Au a decay hindered? Plot from A.Andreyev et al., PRC 80, 024302 (2009) 1/2+ 1/2+

Summary: Charge Radii in Pb region At seems to follow Po unusual trend Back to sphericity in the lightest Au isotopes Magnetic/quadrupole moments will be deduced Large amount of by-product nuclear spectroscopic information on At and Au and their daughter products

ISs and hfss for 10 At isotopes (isomers) were measured for two transitions, 216 nm and 795 nm, The fast switching between these modes of scanning provides much more flexibility to experiment and gives more reliable and complementary data for analysis (especially for atoms without known spectroscopic information). MR-ToF mass separator was used for photo-ions detection for the first time. This method seems to be indispensable for measurements with great surface ionized background and for long lived isotopes with great yield and/or absence of alpha decay mode.Using WM installation for photo-ions detection gives the possibility to obtain wealth of additional nuclear spectroscopic information (decay schemes, spin and parity assignment etc.) without supplementary time requirement.Coordinated (ISOLDE&IRIS) program for Tl isotopes investigation enabled us to use both installation more efficiently.Very interesting results for At and Au isotopes by IS/hfs measurements were obtained: inverse jump of deformation, unexpected spin assignments, shape isomers etc. The study of shape coexistence in the lead region will be continued: to go further for Aus, to fill the gaps and go further for Ats (ISOLDE), to investigate Bi isotopes (IRIS), etc.

Conclusions

Hyperfine structure anomaly for Au isotopes

IRIS: 30 new 189Hg -lines from 189mTl decay are unambiguously identified by hfs pattern and their relative intensities are determinedAdditional nuclear spectroscopic information from Tl isotopes decayISOLDE: decay schemes for some Tl isotopesare determined