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

spectroscopy

IS 534:Beta-delayed fission, laser spectroscopy

and shape-coexistence studies with radioactive 85At beams

IS 534 (addendum):Laser spectroscopy

and shape-coexistence studies with radioactive 79Au beams

Shape Coexistence in the Lead Region studied by laser resonance spectroscopy

• A collaboration of ~30 atomic and nuclear physicists•12 institutions

ISOLDE

Preliminary results for At and Au isotopes!

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

IRIS

Isotope/isomer shift1 ppm

A,Z A-1,Z

Laser beams

Experiments

Mass separation

Target Hot Cavity Extractor Ion Source

Reaction products(neutral)

IonsProtonsTarget material

60 kV

Laser Ion Source at ISOLDELaser Ion Source at ISOLDE

•Isotope 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, or ToF spectra while scanning the frequency

Laser beams

Mass separatorprotons target

ion source

Laser Ion Source at IRISLaser Ion Source at IRIS

A 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 ISOLDEDetection: Windmill System at ISOLDE

Annular Si Si

pure 50 keV beam from RILIS+ISOLDE

Setup: Si detectors from both sides of the C-foil

• Large geometrical efficiency (up to 80%)• 2 fold fission fragment coincidences• ff-γ, γ-α, γ-γ, etc coincidences

C-foils20 mg/cm2 Si detectors

50 keV beam from ISOLDE

SiAnnular Si

ff

ff

C-foil

MINIBALL Ge cluster

A. Andreyev et al., PRL 105, 252502 (2010)

The WM technique requires waiting for the decay of the isotope (usually, α-decay). Not practical for long-lived or stable isotopes (or for β-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/Δm ~ 105

MR-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).

Tape driving device

2(2 1) (2 1)

( )12 1

f i f fi f

i i

F F J F IS F F

F JI

JIJIJIFJIF

JJIIFFK

JIJI

JJIIKKB

KAF

FFFF iffi

,...,1|||,|,

)1()1()1(

)12()12(2

)1()1()1(75.0

2

0,

-10000 0 10000 20000 30000 40000

0

100

200

co

unt

I FC, p

A

, MHz

197Au, stable

200

600

1000

1400 179Au, T1/2

=7.1 s, E=5850 keVAmplitudes of the components:

Positions of the components:

)(1790 Au

)(1970 Au

Ji=1/2

Jf=1/2

F1=I-1/2

F2=I+1/2

F’1=I-1/2

F’2=I+1/2

0

F

QBA ,

Number of components and their relative intensities give the possibility to determine nuclear spin I

-10000 0 10000 20000 30000 40000

0

100

200

co

unt

I FC, p

A

, MHz

197Au, stable

200

600

1000

1400 179Au, T1/2

=7.1 s, E=5850 keV

IS

, ' , ' '( )

'A A A A

NMS SMS

A AF M M

A A

( / )NMS

p e

Mm m

93.0)(,2 AuKrK

Green Beams 90 W @ 532 nm

UV beam18 W @ 355 nm

10kHz rep rate6 - 8 ns pulses

RILIS upgradeRILIS upgrade

CVL to Nd:Yag

Laser ion source at ISOLDENd:YAG lasersDye lasersTi:Sa lasers

3 Ti:Sa lasers:5 GHz linewidthUp to 5 W output power680 – 1030 nm (fund.)35 ns pulse length

RILIS upgradeRILIS upgrade

Dye+Ti:Sa system

Since 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.

2 21/2 3/2

276.9 511 5786 6

nm nm nm

NBL CVLp P d D continuum

Isotope shift δ A,A’:

2, ’ , ’

- '     

'A A A A

A AF r M

A A

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/hfs’s were previously measured for 535 nm transition with reliably established F and M for 186-207Tl:

2.4x107 2.8x107 3.2x107 3.6x107 4.0x1071.2x107

1.4x107

1.6x107

1.8x107

2.0x107

2.2x107

2.4x107

2.6x107

2.8x107

mg

m

A, A'

=A, A'

AA'/(A-A')

King plot for 535 nm and 277 nm lines in Tl

A

,205

(277

nm

)

A,205 (535 nm)

187m

203

207

191m189m

193m

190

186

188

192

194

g

Isotope shift δ A,A’:

2, ’ , ’

- '     

'A A A A

A AF r M

A A

, ' , '

'

'A A A A

A A

A A

Δσ for different transitions should lie on thestraight line with a slope Fλ1/ Fλ2

F535nm, M535nm F277nm, M277nm

King plot

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

183Tl, I=1/2, T1/2=6.9 s

184Tl, I=2, T1/2=11 s

185Tl, I=1/2, T1/2=19.5 s

185Tl, I=9/2, T1/2=1.8 s

183Tl, I=1/2, T1/2=6.9 s

184Tl, I=2, T1/2=11 s

183Tl, I=9/2, T1/2= 53 ms

184Tl, I=10, T1/2= 37 ms

180Tl, I=(4,5), T1/2=1.1 s

181Tl, I=1/2, T1/2=3.4 s

182Tl, I=(4,5), T1/2=3.1 s

179Tl, I=1/2, T1/2= 0.23 s

IRIS

IRIS & ISOLDE

ISOLDE

186Tl, I=10, T1/2= 2.9 s

195mTl, I=9/2, T1/2=3.6 s

197mTl, I=9/2, T1/2=0.54 s

Hyperfine structures observed for 184Tl with different detection modes

with frequency of the narrow-band laser fixed at the marked positions isomer selectivity is obtained and one can investigate properties of the pure isomer state

hfs of the previously unknown isomer (I=10)

ground state hfs

Isomer selectivity for Isomer selectivity for 184184Tl (ISOLDE)Tl (ISOLDE)

Shape coexistence and charge radii in Pb Shape coexistence and charge radii in Pb regionregion

?

85At?

2011: 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

At

Photoionization scheme for the radioactive element At

Optimal photoionization scheme.Narrow band lasers for 1st and 2nd transitions

216 nm

795 nm

532 nmIP

6p5, J=3/2

6p47s, J=3/2

6p48p(?), J=3/2 or 5/2

In collaboration with TRIUMF-ISAC radioactive ion beam facility with the TRILIS laser ion source

IP (At)=9.317510(84) eV 2 2

Mn

RIP E

n

Precise determination of the Ionization Potential for the radioactive element At

15410.9 15411.0 15411.1 15411.2 15411.3 15411.4

0

1000

2000

3000

4000

5000

6000 hfs for m.s. (I=10) hfs for g.s. (I=3)

, cm-1

N

198At15411.123pure g.s. (I=3)

15411.0 15411.1 15411.2 15411.3 15411.4 15411.5

0

200

400

600

800

1000

1200

1400

1600

1800

hfs for g.s. (I=9/2) hfs for m.s. (I=1/2)

N

, cm-1

197At15411.154pure g.s. (I=9/2)

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

IS534: Isomer selectivity for IS534: Isomer selectivity for 197,198197,198AtAt

IS534: Astatine HFS spectraIS534: Astatine HFS spectra

1st step scanning is better for Δ<r2> extraction2nd step scanning is better for hfs resolution (Q and μ determination). But to decipher these hfs’sone should know J for 58805 cm-1 level (5/2 or 3/2)

2, ’ , ’

- '     

'A A A A

A AF r M

A A

216 nm

795 nm

532 nmIP

-5000 0 5000 10000 15000

0

100

200

300

400

500

600

700

800

N

, MHz

197At, I=1/2, 2nd step scan

The number of peaks (4 rather than 3) unambiguously points to J=3/2 for 58805 cm-1 atomic state in At

IS534:IS534: Additional atomic spectroscopic information Additional atomic spectroscopic information

for Astatinefor Astatine

216 nm

795 nm

532 nmIP

58805 cm-1, J=3/2 or 5/2

J=3/2

J=3/2

F1=1

Jf=5/2

F2=2

F’1=2

F’2=3

Ji=3/2

I=1/2

Jf=3/2

F1=1

F2=2

F’1=1

F’2=2

Ji=3/2

795 nm

-5.0E+07

-4.0E+07

-3.0E+07

-2.0E+07

-1.0E+07

0.0E+00

0.0E+00 2.0E+07 4.0E+07 6.0E+07

A,205(795nm) A

,20

5 (2

16

nm

)

197g

197m

207

198g198m

217

, ' , '

'

'A A A A

A A

A A

Isotope shift δ A,A’:

2, ’ , ’

- '     

'A A A A

A AF r M

A A Δσ for different transitions should lie on a straight line with a slope Fλ1/ Fλ2

King plot for 216 nm and 795 nm lines King plot for 216 nm and 795 nm lines in Atin At

F216/F795(At)=-2.26(8)

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

IS534IS534 October 2012:October 2012:Charge radii of At isotopesCharge radii of At isotopes

WM

WM

MR-ToF

FC

108 110 112 114 116 118 120 122 124 126 128 130 132 134

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Po At At isomers

<r2 >

N,1

26, f

m2

N

Astatine seems to follow Polonium δ<r2> 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:October 2012:IS534 experiment at ISOLDE – Au IS534 experiment at ISOLDE – Au

isotopesisotopes

•Are the light Au isotopes deformed?

•What are the spins of ground and isomeric states?

267.7 nm

306.6 nm

674.1 nmIP

autoionizing state

Au ionization scheme

Au hfs spectraAu hfs spectra

F1=0

Jf=1/2

F2=1

F’1=0

F’2=1

Ji=1/2

I=1/2

0—>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)

F’2

F’1

F1

F2

Is it possible to discriminate between I=1/2 Is it possible to discriminate between I=1/2 and I=3/2 for Au isotopes by hfs spectra?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+ calculated

177Au (WM)

Number of peaks and their intensities ratiofix ground state spins of 177,179Au: I=1/2

Why is 1/2+1/2+ 181Tl177Au decay hindered?

Plot from A.Andreyev et al., PRC 80, 024302 (2009)

1/2+

1/2+

~1.6N , pure sph. 3s1/2, (as in the heavier Tl’s)

~1.1N , (preliminary) mixed/def/triaxial 3s1/2,/d3/2

HF>3 I=3/2

Summary: Charge Radii in Pb regionSummary: Charge Radii in Pb region

• At seems to follow Po unusual δ<r2> 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

1. IS’s and hfs’s 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).

2. 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.

3. 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.

4. Coordinated (ISOLDE&IRIS) program for Tl isotopes investigation enabled us to use both installation more efficiently.

5. 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 Au’s, to fill the gaps and go further for At’s (ISOLDE), to investigate Bi isotopes (IRIS), etc.

Conclusions

5000

10000

15000

0

400

800

1200

0400800

1200

0200400600

1000

2000

3000

-12000 -9000 -6000 -3000 0 3000 6000 9000 120000

50010001500

A=191m, I=9/2E= 265, 326 keV

T1/2= 313 s

A=193m, I=9/2E= 365 keV

T1/2=127 s

A=195m, I=9/2E=384 keV

T1/2=3.6 s

(MHz)

coun

tsco

unts

coun

tsco

unts

IS

A=197m, I=9/2E=386 keV

T1/2=0.54 s

coun

tsI FC

, arb

. uni

ts

A=205, I=1/2Faraday cupstable isotope

A=189m, I=9/2E= 216 keV

T1/2= 84 s

Hyperfine structure anomaly for Au isotopesHyperfine structure anomaly for Au isotopes

,22

11

2211 , Aln

AlnA

lnln a

a )()(1 2211

,

, 2121

2

2211

1

221122

2

11

1lnln AAAA

Alnln

Alnlnln

AlnA

)1()(

)(0

00

0

Anl

A

A

A

A

AAA nla

nla

I

I

IRIS: 30 new 189Hg γ-lines from 189mTl decay are unambiguously identified by hfs patternand their relative intensities are determined

Additional nuclear spectroscopic information Additional nuclear spectroscopic information from Tl isotopes decayfrom Tl isotopes decay

ISOLDE: decay schemes for some Tl isotopesare determined

183Tl, I=1/2, T1/2=6.9 s

184Tl, I=2, T1/2=11 s

185Tl, I=1/2, T1/2=19.5 s

185Tl, I=9/2, T1/2=1.8 s

186Tl, I=10, T1/2=2.9 s

195Tl, I=9/2, T1/2=3.6 s

197Tl, I=9/2, T1/2=0.54 s

…

186Tl, I=7, T1/2=27.5 s

187Tl, I=9/2, T1/2=15.6 s

188Tl, I=7, T1/2=71 s

190Tl, I=7, T1/2=3.7 m

189Tl, I=9/2, T1/2=84 s

190Tl, I=2, T1/2=2.6 m

191Tl, I=9/2, T1/2=5.2 m

192Tl, I=7, T1/2=10.8 m

192Tl, I=2, T1/2=9.6 m

194Tl, I=7, T1/2=32.8 m

193Tl, I=9/2, T1/2=2.1 m

194Tl, I=2, T1/2=33 m

203Tl, I=1/2, stable

207Tl, I=1/2, T1/2=4.77 m

repeated for another atomic transition

(276.9 nm)

for King-plot calibration

21/26p P 2

3/26d Dpreviously measured for

23/26p P 2

1/27s S

transition (535.2 nm)