Nuclear Charge Radius
Measurement of
Beryllium Isotopes
Ch. Geppert1,2, A.Krieger1, R.M. Sànchez3,
D. Tiedemann1, M. Zakova1,
M.L. Bissell4, K. Blaum5, N. Frömmgen1,
M. Hammen1, J. Krämer1, K. Kreim5,
T. Neff3, R. Neugart1, D.T. Yordanov5,6
and W. Nörtershäuser1,3
1)
2)
3)
4)
5)
6)
Institut für Kernchemie, Johannes Gutenberg-Universität, Mainz
Helmholtzinstitut Mainz, Mainz
GSI Gesellschaft für Schwerionenforschung GmbH, Darmstadt
Instituut voor Kern-en Stralingsfysica, Katholieke Universiteit, Leuven
MPI für Kernphysik, Heidelberg
CERN, ISOLDE Physics Department, Geneva
Laser
Laser
Spectroscopy
Spectroscopy
of of
Highly
Highly
Charged
Charged
Ions
Ions
andand
Exotic
Exotic
Radioactive
Radioactive
Nuclei
Nuclei
Outline
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
•Introduction to Halo Nuclei
see talks from B. Jonson, P. Müller,
M. Brodeur, I. Tanihata and ….
•Charge Radius
mass shift and field shiftcoefficient calculation
Isotope Shift
•Properties of Beryllium Isotopes
isotopic chain, D1 & D2 transition,
on-line production
•Schematics of Collinear Laser Spec.
classical design, technical challenges
(voltage determination)
•Experimental Setup 2008
schematic laser system and
measurement procedure
•Experimental Setup: Upgrade 2010
ion-photon coincidence
•Results and Discussion
development of charge radius along
isotopic chain, comparison FMD calc.
Isotope Shift Contributions
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
Isotope 1
Isotope Shift := Frequency difference in an
electronic transition between two isotopes
IS
Mass Shift Term
~ 10 GHz
MS
nuclear motion around center of mass
+
2Z |(0)|2
3
1-10 MHz
r
Field Shift Term
finite size of the nucleus
V(r)
=
Isotope Shift
Isotope 2
r
Isotope Shift Calculations
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
• Z. C. Yan, W Nörtershäuser and G. W. F. Drake, Phys. Rev. Lett. 100, 243002 (2008).
• M. Puchalski and K. Pachucki,
Phys. Rev. A 78, 052511 (2008).
measurement output
theory calculation
=
Isotope Shift
IS
Mass Shift Term
~ 10 GHz
Isotope
Transition
7Be
D1
/ MHz
-49 225.779(38)
9Be
D1
0
10Be
D1
17 310.441(12)
D2
17 312.569(13)
11Be
D1
31 560.294(34)
12Be
D1
43 390.168(39)
D2
43 395.499(39)
9,A
MS
+
dimension of interest
2Z |(0)|2
3
1-10 MHz
r
Field Shift Term
MS
(reference)
F= 2Z
3
|(0)|2
beryllium 1+ ion :
F=-17.02 MHz/fm²
Introduction to Beryllium – I
neutron drip line
proton drip line
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
N=8
2p3/2
F=0,1,2,3
2p½
F=1
2p½
F=2
7, 9
Be+
2s½
D1
313 nm
10,12Be+
F=1
11Be+
F=0
2s½
2s½
F=1/2
0
F=0
2p½
F=1/2
F=1
F=2
I=3/2
D2 transitions not resolved
F=1
1/2
Introduction to Beryllium – II
N=8
11Be:
well known archetype of oneneutron halo nucleus Sn=0.5 MeV
12Be:
halo nucleus?  maybe not ?!
decrease in matter radii trend,
Sn=3.2 MeV S2n=3.7 MeV
I. Tanihata et. al. PRL 55, 2676 (1985)
I. Tanihata et. al. PL B 206, 592 (1988)
14Be:
well known halo-nucleus;
two- or four-neutron halo ?
neutron drip line
proton drip line
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
Elastic Scattering 12Be at GSI
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
Results of scattering experiments at cave C @ GSI using the IKAR detector
strong increase at high momentum
transfer indicates halo-character
Rmatter=2.82 ± 0.12 fm
Rcore=2.18 ± 0.10 fm
Rhalo=5.41 ± 0.32fm
pictures taken from: PhD thesis Stoyanka Ilieva 2009 @ University Mainz / GSI:
"Investigation of the nuclear matter distribution of the exotic 12,14Be and 8B by elastic proton scattering in inverse kinematics”
Production of Radioactive Isotopes:
the ISOLDE Facility @ CERN
• 1.4 GeV pulsed proton
beam from PSB
• ionization at RILIS
(resonant laser ion source)
• GPS mass separator
(no RFQ cooler)
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
Production of Radioactive Isotopes:
Beryllium Yields @ ISOLDE
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
Laser
laser
ion source
für die resonante Ionisation
Extraktion
extraction
Erdpotential
Hochspannung
high
voltage
Ionisation
ionization
Effusion
effusion
Target
UC2)
UC (z.B.
target
x
Half life
Yield (ions/ C)
7Be
53.12 d
1.4 E+10
10Be
1.51E+6 a
6.0 E+09
11Be
13.8 s
7.0 E+06
12Be
23.6 ms
1.5 E+03
14Be
4.35 ms
4.0 E+00
2008
Isotope
2010
Protonenstrahl
proton
beam
Transfer
Röhre
transfer
line
upgrade: ion-photon
coincidence technique
Working Principle of
Collinear Laser Spectroscopy
high voltage
ion source
laser beam
+
(fixed frequency)
+
deflector unit
(10° horizontal)
ion optics
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
Doppler-tuning of ion
beam velocity (±10 kV)
1 
  L
  2eU / m
1  2
+
quadrupole lens
velocity bunching by ion beam
acceleration (30 - 60 kV)
E  const.
   0
E
2eUmc 2
scanning
high voltage
charge
exchange
cell
optical
detection
0
laser beam
Technical Challenges of
Collinear Laser Spectroscopy
high voltage
ion source
laser beam
+
(fixed frequency)
+
ion optics
deflector unit
(10° horizontal)
+
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
Doppler-tuning of ion
beam velocity (±10 kV)
1 
  L
  2eU / m
1  2
+
Voltage Uncertainty
+
typical 10-4
6 V @ 60 kV
11 MHz artificial isotope shift
10-times larger than required
resolution
Straylight Background
laser produces strong straylight background light in (classical) optical detection
lower detection limit 105 ions / s
quadrupole lens
+
charge
exchange
cell
scanning
high voltage
optical
detection
0
0
laser beam
Improved Collinear Laser
Spectroscopy Layout
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
high voltage
laser beam
(collinear)
ion source
+
ion optics
 c   0    1   
deflector unit
(10° horizontal)
+
 a   0    1   
+
+
 a  c 
2

 1 
2

2
0
  02
+
scanning
high voltage
optical
detecton
cancel out ß (=voltage) dependance
Requirements:
• two independent laser systems
• measure absolute frequencies
• accuracy:
< 10-9
0
laser beam
(anti-collinear)
Experimental Setup:
Laser System Layout
Servo
Dye Laser
(Anticollinear)
20 m fiber
Frequency
Doubler
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
Shaping
Optics
beam
blocker
Photodiode
PMT
Frequency
Comb
B
50000
COLLAPS
Be+Beam
40000
Retardation
Y A xis T itle
Rubidium
Clock
30000
20000
10000
Deflector
0
-1 5 0 0
-1 0 0 0
-5 0 0
0
500
X A x is T itle
Dye Laser
(Collinear)
beam
blocker
20 m fiber
Frequency
Doubler
I2
FM-Iodine Lock
Servo
1000
1500
Scanning Procedure
1.
locking collinear laser frequency to feasible iodine line
2. choosing proper scanning range for deceleration voltage to
scan over all resonance lines for collinear laser
3. adapt anti-collinear laser lock point on frequency
comb such, that anti-collinear spectra can be
observed in same voltage range
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
Online Spectra of 10,11Be
(2010)
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
10Be
10Be
> 200x
> 200x
11Be
6x
11Be
6x
Upgrade 2010:
Ion-Photon-Coincidence
5 x108 10Be-ions/pulse
scan time: 3 minutes
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
30.000 10Be-ions/pulse
scan time: 30 minutes
Online Spectra of 12Be
12Be
26x D1
14x D2
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
Systematic Uncertainty Budget
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
laser
laser beam
laser
beam
laser
ion beam
ħk
laser
Uncertainty
Contribution [kHz]
Laser-/ion beam alignment
al
500
Uncertainty of the atomic clock (frequency comb)
fc
40
Photon recoil
ph
100
syst.
511
total systematic uncertainty
Online Beamtime Results:
Overview Table
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
Measurement of the absolute transition frequencies 0 ,
calculations of the isotope shift IS ,
the rms change in charge radius < r2>
and the nuclear charge radius r
Isotope
0 [MHz]
IS
[MHz]
FS
[MHz]
< r2> [fm2]
r [fm]
7Be
-49 236.9(9)
-11.11(97)
0.66(6)
2.646(16)
9Be
0
0
0
2.519 (12)*
10Be
17 323.4(8)
13.01 (83)
-0.77 (5)
2.361 (17)
17 325.6(9)
13.03(92)
-0.77(9)
2.361(23)
11Be
31 564.7(7)
4.42(72)
-0.26(4)
2.466(15)
12Be
43 391.5(9)
1.29(95)
-0.08(6)
2.503(17)
43 397.0(9)
1.50(99)
-0.09(9)
2.501(22)
10Be
12Be
(D2)
(D2)
better than 1 MHz
rel. uncertainty ~1%
* J. A. Jansen, et.al.
Nuclear Physics A 188 (1972)
Online Beamtime Results:
Charge Radii Plot (2008)
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
7Be
Nuclear charge radius / fm
2,7
11Be
9Be
2,6
11Be
2,5
2,4
10Be
8Be
2,3
7
8
9
10
11
Be Isotope
12
13
14
Online Beamtime Results:
Charge Radii Comparison 2008 - 2010
Nuclear charge radius / fm
2,7
Krieger et al., accepted by PRL
2008 – D1
arXiv:1202.4873v1
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
2010 – D1
2,6
*
2,5
2,4
2,3
7
* = reference isotope 9Be
8
9
10
11
Be Isotope
from electron scattering: rc(9Be) = 2.519(12) fm,
12
13
14
[J.A. Jansen et al., Nucl.Phys.A 188, 337 (1972)]
Comparison Experiment
to FMD Theory
2008 - D1
2010 - D1
FMD multiconfig.
calculation by Th. Neff
2,7
Nuclear charge radius / fm
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
2,6
1d3/2 4
2s1/2
1d5/2 2
1p1/2
1p3/2
6
2
4
2,5
pure
(sd)²
2,4
2,3
1s1/2 2
12Be
pure p²
N=8
7
8
9
10
11
Be Isotope
12
13
14
strong admixture
of (sd)²-levels
Comparison Experiment & Theory:
splitting isotope shift
splitting isotope shift
subtracting isotope shifts in D1 and D2 transition
12-10
Experimental
Pachucki &
Puchalski
Yan & Drake
Be
12-9
Be
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
test of theoretical
predictions
splitting isotope shift
shows
excellent agreement….
11-9
Be
10-9
Be
... among theoretical
calculations
7-9
Be
-8
-6
-4
-2
0
2
4
Splitting Isotope Shift / MHz
6
8
… among theory and
experiment
Conclusion
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
two laser spectroscopy beamtime
runs at ISOLDE 2008 and 2010
measured
although 2x complete (re-)installation
of laser system etc.
high consistency / reproducibility
high resolution method for shortlived radioactive isotopes
IS determination precision < 1 MHz
thanks to high accuracy calculation of
mass shift (Drake, Yan, Pachucki,..)
charge radius determination better 1 %
comparison with FMD calculations
good agreement, strong (sd)²-admixt.
test atomic theory calculations with
experimental data
excellent agreement in splitting isotope
shift
7-11Be
and
9-12Be
Outlook 14Beryllium
production yields too low for current online-facilities
(at least for collinear laser spectroscopy)
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
Thank you for your attention
Laser Spectroscopy of
Highly Charged Ions and
Exotic Radioactive Nuclei
Working group LaserSpHERe
www.kernchemie.uni-mainz.de/laser
or Google: „lasersphere“