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: [email protected]
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