1. Collinear laser spectroscopy of 42g,mSc
Liam Vormawah
University of Liverpool

2. Contents Collinear laser spectroscopy at IGISOL IV
Hyperfine structure, isotope shift and nuclear properties obtained
Spectroscopy of 42g,mSc
Results, conclusions and future work

3. Collinear laser spectroscopy
Laser beam
Ion beam
Photon emitted
from ion
Excited
state
Ground
Photon from laser
Excitation
of electron
Electron
de-excites; photon emitted e-

4. Hyperfine structure and isotope shiftz y x

5. Hyperfine structure and isotope shift
Fine structure J- states split and perturbed
Splitting due to magnetic dipole moment, m
Perturbation due to electric quadrupole moment, Q
Angular momentum coupling analogous
(FS)
(HFS)
Isotope shift, dnA,A’
Difference in centroid of HFS between two isotopes
Two components – mass shift and field shift
Change in mean- square charge radius, d<r 2>, obtained from field shift
Transition-dependent atomic factors F and M must be correct!

6. Setup at JYFL IGISOL
IGISOL IV – Ion Guide Isotope Separator On- Line; 4th incarnation
Located at University of Jyväskylä, Finland

7. The IGISOL IV Laboratory
Cooler
IGISOL ion guide
(Gas cell with thin-foil target)
55o dipole analyser magnet
Beam
switchyard
Ion beam
to laser setup
JYFLTRAP*
Cyclotron
beam line
(from K-30 or K-130)
*Not actually part of laser spectroscopy setup

8. The RFQ cooler-buncher
Reduces energy spread of ions…
2-d ion trap filled with He gas
Ions cooled to less than 1eV
Reaccelerated to virtually the same energy
…and also photon background!
Ions accumulated and released periodically
Only count photons when ion bunch and PMT are in alignment .
Endplate potential Z
(Cooler axis)
200ms
20μs
Photomultiplier
tube
Ion bunch
Laser
beam
Doppler tuning electrodes
Ion accumulation
Ion release
Linear ion trap filled with buffer gas.
Ions enter cooler with range of energies (high energy spread); collisions with gas molecules reduce ions’ energy to hardly any.
When they leave the cooler, the ions see the same potential and are excited to virtually the same energy (energy spread reduced!)
Can also bunch the ions – potential applied to cooler endplate for 200ms (accumulate ions in cooler); release ions for 20μs. Set electronic gate on detection system to only count photon if ion bunch is in front of detector at that time. This reduces laser backscatter.

9. 42Sc structure p n 28 28 20 20 2p1/2 1f5/2 2p3/2 1f7/2 1d3/2 2s1/2

10. 38K structure p n 28 28 20 20 2p1/2 1f5/2 2p3/2 1f7/2 1d3/2 2s1/2

11. Sc Ca K Spectroscopy of 42g,mSc21
42Sc – self-conjugate nucleus; i.e. N=Z
Doubly-magic 40Ca core plus two valence nucleons (1p+1n)
I=0 ground state
I=7 isomer
Larger radius expected for I=0 state
38K previously studied by Bissell et al. (2014)
40Ca core minus (1p+1n)
I=3 ground state
I=0 isomer
Isomer larger than ground state
Expect the opposite in 42Sc…
Line of N=Z Ca 40 20 K 38 19

12. Experimental methodology
42Sc produced using 40Ca(a,pn)42Sc reaction
30MeV a beam
Natural calcium target
Spectra taken on 363.1nm 3d4s 3D2 → 3d4p 3F3 transition
Ground and metastable states present in 42Sc spectra
J=2 → J=3 transition occurs in singly-charged (Sc+) ion
Transition from naturally- populated metastable state – optical pumping showed no improvement
42Sc

14. Conclusions and future work
Results as predicted!
42Sc ground state (I=0) larger than isomer (I=7)
Results consistent with those of Avgoulea et al. (2010)
Theoretical input for comparison
Shell model calculations of moments and charge radii
Further investigations along the N=Z line
Isomers in other self-conjugates – e.g. 26Al…

15. Collaborators University of Liverpool University of Manchester
L. J. Vormawah, B. Cheal, C. Wraith
University of Manchester
P. Campbell, A. Dicker, S. Kelly
KU Leuven
S. Geldhof, G. Neyens, H. Heylen
University of Jyväskylä
A. Jokinen, I. D. Moore, A. Voss, M. Reponen

16. Thanks for listening!
Any questions?