67 860 cm-1

39 081.19 cm-1

50 934.89 cm-1

�1 = 255.80 nm

�2 = 843.37 nm

0 cm-1

�3 = 588 nm to 604 nm

Po

IEliterature

6p 7s S3 5

2

6p 7p P3 5

2

6p P4 3

2

16740

16760

16780

16800

16820

16840

16860

16880

16900

16920

16940

0.0

0.2

0.4

0.6

Sca

n 3

Fit

Ion Current (pA)

Gro

up

s=

6 t

o=

44

gg

Excita

tio

n E

ne

rgy

Ab

ove

2E

xcite

d S

tate

nd

5000 5500 6000 6500 7000 7500 8000 8500 90000

50

100

150

200

250

Energy (keV)

Counts

per

1 k

eV

5900 5950 6000 6050 61000

50

100

150

200

250

Co

un

ts p

er

1 k

eV

Energy (keV)

218Po

218Po

214Po

217 218At/ Rn 213

Po

�-spectrum= 218um

0

50

100

150

200

250

300

350

400

6400 6500 6600 6700 6800 6900

Energy (keV)

Co

un

ts p

er

1 k

eV

Energy (keV)

Co

un

ts p

er

1 k

eV

5000 5500 6000 6500 7000 7500 8000 8500 90000

40

80

120

160

200

217Po

217Po

216

213

Po/Fr

217At

217 216Rn/ At

213Po

216Po/

213Fr

241Am

�-spectrum= 217um

208Po

216 +Po, I=0 217 +Po, I=(9/2 ) 218 +Po, I=0

a) b)

c) d)

e)

Figure 3 | Results from the in-source laser spectroscopy of polonium. a) Rydberg spectrum of Po. b) Ionization scheme for Po. The last step

was scanned to obtain a). The second step was scanned and -decay spectra c,d) The gated signal reveals the hyperfine spectra displayed in

e). Figures taken from [8]

�

In-source laser spectroscopy of polonium isotopes:From atomic physics to nuclear structure

Dr. Sebastian Rothe

Sources, Targets & Interactions Group

Engineering Department

CERN

Email: Sebastian.ROTHE@cern.ch

Imp

rove

d S

etu

p

In-source laser spectroscopy is a powerful method to investigate optical

spectra of radioisotopes created at on-line radioactive ion beam facilities

such as CERN-ISOLDE.

Through the measurements of isotope shift and hyperfine splitting of the

atomic spectrum an isotope one can derive nuclear ground state

properties (change in mean-square charge radius < >, spin, magnetic

dipole moment, el. quadrupole moment) [1].

Figure shows the evolution of < > measured for even Z elements

from Pt to Ra. The most prominent feature is the extreme odd-even

staggering of the n-deficient Hg. For Po, the onset of deformation is

clearly seen as a departure from the trend-line of the largely spherical

lead isotopes [2,3]. For the n-rich region, a reversal of the odd-even

�

�

r

r

2

21

Intr

od

uct

ion

staggering (seen in Ra) would be an indicator of octupolar deformation

interpreted as a pear-shaped nucleus [4]. The results shown for n-rich Po

were obtained at CERN-ISOLDE using the Resonance Ionization Laser Ion

Source (RILIS) [5] as a precision spectroscopy tool. Missing data is

attributed to the overwhelming background of Fr contamination. The

RILIS makes use of step-wise resonant excitation of the atom using lasers

tuned to specific optical transitions of an element. A last step releases the

electron by lifting it above the ionization energy (IE).

In fact the IE is a fundamental property of the atom that can also be

studied by using the RILIS . The precision of

the IE value of Po can be improved by spectroscopy of high-lying Rydberg

states as demonstrated recently for At [6].

in-source laser spectroscopy

S. Rothe , A.N. Andreyev , S. Antalic , A.E. Barzakh , B.Bastin , T.E. Cocolios , D.V. Fedorov , V.N. Fedosseev , D.A. Fink ,

K.T. Flanagan , L. Ghys , M. Huyse , N. Imai , T. Kron , K.M. Lynch , B.A. Marsh , D. Pauwels , E. Rapisarda ,

S.D. Richter , R.E. Rossel , M.D. Seliverstov , A.M. Sjödin , C. Van Beveren , P. Van Duppen and K.D.A Wendt

1 2 3 4 5 6,1 4 1 7,8

6 9,10 9 11 12 9 1 10 1

12 1,12 4 5 9 9 12

1

2

3

4

5

6

CERN, CH-1211 Geneva, Switzerland

Department of Physics, University of York, York YO10 5DD, United Kingdom

Department of Nuclear Physics and Biophysics, Comenius University, SK-842 48 Bratislava, Slovakia

Petersburg Nuclear Physics Institute, NRC Kurchatov Institute, 188300 Gatchina, Russia

Grand Accelerateur National d'Ions Lourds, FR-14076 Caen, France

School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom

7

8

9

10

11

12

Max-Planck-Institut für Kernphysik, DE-69117 Heidelberg, Germany

Fakultät für Physik und Astronomie, Ruprecht-Karls Universität, DE-69120 Heidelberg, Germany

Instituut voor Kern- en Stralingsfysica, KU Leuven, BE-3001 Leuven, Belgium

Belgian Nuclear Research Centre SCK - CEN, BE-2400 Mol, Belgium

High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan

Institut für Physik, Johannes Gutenberg-Universität Mainz, DE-55128 Mainz, Germany

Re

sult

s a

nd

An

aly

sis

The ionization energy of polonium

�

�

�

�

�

Scan of third step ( reveals converging series of Rydberg levels (Figure a)

5 Series to different quantum defects can be distinguished for small quantum numbers n

Conventional Rydberg analysis yields IE(Po)=67896(1) cm

Perfect agreement with results obtained simultaneously at TRIUMF-ISAC [14]

An alternative analysis method was successfully applied: Enables direct extraction of the IE

from data through correlation with theoretical spectra

3

-1

�3)

(Figure a)

(Figure b)

4

4

Odd-even staggering of polonium

�

�

�

�

�

�

�

NB-Ti:Sa ( ) was scanned across the�2 6p 7p P energy level

IKS Windmill recorded -spectra at each wavelength step

The Fr background was fully suppressed by LIST

Gates were applied for characteristic -energies (Figures c,d)

Changes in mean-square charge radius with respect to Po were extracted (Figure a)

Relative odd-even staggering plot (Figure b) indicates normal odd-even staggering in contrast

to the reversed odd-even staggering Rn and Ra

Po marks a lower limit of the end of the region of inverted odd-even staggering.

3 5

210

2

�

� 3

5

5

[1] E. W. Otten, Treatise on Heavy-Ion Science, Vol. 8, p. 517(1989)

[2] T. E. Cocolios et al., Phys. Rev. Lett., 106:052503 (2011)

[3] M. D. Seliverstov et al., Phys. Lett. B 719, 362-366 (2013)

[4] L. P. Gaffney et. al.,Nature 497, 199–204 (09 May 2013)

[5] V. N. Fedosseev et al., Rev. Sci. Instrum. 83, 02A903 (2012)

[6] S. Rothe et al., Nat. Commun. 4, 1835 (2013)

[7] K. Blaum,et al., NIMB 204, 331–335 (2003)

[8] D. A. Fink, Thesis, Ruprecht-Karls Universität, Heidelberg, Germany (2014)

[9] D. A. Fink et al., Nucl. Instrum. Meth. B 317, 417421 (2013)

[11] S. Rothe, Thesis, Johannes Gutenberg-Universität, Mainz, Germany (2012)

[12] S. Rothe et al., Nucl. Instrum. Meth. B 317, 561564 (2013)

[13] R. E. Rossel et al., Nucl. Instrum. Meth. B 317, 557560 (2013)

[14] S. Raeder, D.Fink et al. (in preparation)

[10] B. A. Marsh et al., Nucl. Instrum. Meth. B 317, p.550 (2013)

Co

nta

ct

?

Neutron number

Ch

an

ge

in

nu

cle

ar

me

an

sq

ua

r e c

ha

rge

ra

diu

s<

r>

�2

Figure 1|Changes in nuclear charge radius for even-Z nuclei from Pt to Ra [8].

Note the strong odd-even staggering for Hg around N=104. The odd-even

staggering is reversed for n-rich Rn and Ra - indicating octupole deformation.

Development of the Laser Ion Source and Trap (LIST) [7,8]

Combination of linear RFQ trap and surface ion repeller

significantly reduces the isobaric background

selectivity improved by ~500 (suppression of up to 10 ,loss of 20) [9]

�

�

�

4

Po

U

LIST

Po

Ti:Sa

RILIS Dye Laser System

RILIS Ti:Sa Laser System

Dye THG

Dye

NB-Dye

SHG

FHG

SHG

Nd:YAG PX1

Nd:YAG PX2

Nd:YAGTHG

DelayGenerator

10 kHzMaster Clock

wavemeter

Ti:Sa

NB-Ti:Sa

Target and

Ion Source

U

�-SpectroscopyFaraday cup

Windmill

LabVIEW DAQ

wavemeter

Po

Po

U

U

U

UU

U

Ca

AuU

U

UFr

UU

PoUPo

PoPoPoPo

Po

Po

FrFr

FrFrPoPo Po

Po

Fr

Po

Fr FrFr

60 kV

Repeller

Protons

+

+

RF - Ion Guide

217

+Po

218

+Po

208

+Po217

+Po

Isotope Separator

Magnet

Extractor

Figure 2 |Setup for the in-source laser spectroscopy of polonium. The computer controlled tunable dye and Ti:Sa lasers are sent through the ISOLDE separator magnet into the target and

ion source assembly. The reaction products created by the proton-induced nuclear reaction are vaporized and are collimated by the hot cavity ionizer. The LIST repeller repells surface

ionized contaminants such as Fr. The lasers ionize the atoms entering the RFQ ion guide. The ions are accelerated to 60kV, mass-separated and then detected by a FC or the WINDMILL.

233

2

33

Advanced RILIS laser spectroscopy capabilities [10]

�

�

�

solid-state titanium:sapphire (Ti:Sa) lasers [11]

computer controlled dye laser system, Nd:YAG pumped

narrow bandwith Ti:Sa operation (NB-Ti:Sa, < 1 GHz) [12]

LabVIEW based data acquisition system [13]

automated scanning of NB Ti:Sa laser

recording and live display of the spectra

integration of ISOLDE Faraday Cups, IKS Windmill , ISOLTRAP MR-ToF

�

�

�

Figure 4 | Determination of the ionization energy of polonium. a) Rydberg formula fitted to the peak positions of the S series observed in the spectrum.

[8] b) Correlation matrix. Correlation function ( , ) between the data and the theoretical Rydberg spectrum. A cut at =0.31 reveals a single peak

structure. The centroid of the Gaussian fit shown in the top panel equals the ionization limit. A cut at this energy reveals the different series.

f Ec c c� �

10

0

20

0

30

0

40

0

50

0

-0.2

0.0

0.2

0.4

0.6

16958 16960 16962 16964 16966

100200300400500

16600

16700

16800

16900

20 25 30 35

-0.1

0.0

0.1

Excita

tio

n E

ne

rgy (

cm

)-1

ionization limitSeries S

Re

sid

ua

ls (

cm

)-1

a) b)

Ionization limit Ec

qu

an

tum

de

fect

�c

a)

�<

r>

(fm

)2

2

A,2

10

Neutron number

b)

Neutron number100 110 120 130 140 150

Rela

tive o

dd-e

ven s

taggering (

fm)

2

0

0.1

0.2

0.3

0.4

0.5

Pb

Po

Rn

Ra

!

Figure 5 | Results for the relative changes in mean square charge radius. a) for the Po chain. b) Odd-even staggering for the even Z nuclei (trend

removed). The arrow indicates the newly determined value for Po. Po exhibits a normal odd-even staggering.217 217

1

1

Re

fere

nce

s

principal quantum number n

Jun

e 2

01

4