This presentation describes my research on a hyperfine transition within the iron atom, using a laser setup for evaporating iron and measuring its spectrum.
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Bachelors Thesis Presentation
1. Atomic beam production and spectroscopy on the
iron 3d64s2 5D4 3d64s4p 5D4 transition
Bachelors presentation by Joost Jan van Barneveld
Facilities Laser Centre Vrije Universiteit
Supervisors Prof. Dr. Wim Ubachs
Dr. Eric-Jan van Duijn
2. Overview
• Motivation – Why spectroscopy on Iron ?
• Atomic beam production and setup
• Theory of spectroscopy
• Results
– Resolving isotopes
• Discussion
– Resolving hyperfine splitting
• Conclusion
• Debate
3. Introduction
• Shifting constant results in
renewed interest in spectroscopy1,2
• Iron is a suitable element:
– High universal abundance
– High mass number, Z=56
• Ehf Z g (S I ) 4 3
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
[1] PRL 96, 151101 (2006) – W. Ubachs et al - Indication of a Cosmological Variation of the Proton-Electron Mass Ratio Based on Laboratory Measurement and Reanalysis of H2 Spectra
[2] Nucl. Physics B 653 (2003) 256-278 - T. Dent, M. Fairbairn,
4. Beam production & setup
• Elements need to be in gas phase for LIF
spectroscopy
• Evaporated iron forms a gas
• Evaporation requires heat: 1808K
Thermogravimetric Measurement of the
Vapor Pressure of Iron from 1573 K to 1973 K
Frank T. Ferguson, Joseph A. Nuth, and Natasha M. Johnson
J. Chem. Eng. Data, 2004, 49 (3), 497-501 • DOI:
10.1021/je034152w
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
5. Beam production & setup
1. Fix the sample (iron curls)
2. Heat the sample
3. Contain the heat
4. Minimise speed distribution
(Doppler width)
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
6. Beam production & setup
Fixing the sample
• Sample holder needs to withstand the heat
• Tantalum sheet (.5mm) is suited
• Melting point 3269K
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
7. Beam production & setup
Heating the sample
• Hit the sample holder with inrared laser
light (Nd:YAG 1064 nm)
• Sample absorbs the light and heats up
• Hot object emits blackbody radiation
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
8. Beam production & setup
Containing the heat
• Reflect IR radiation back to sample
• Minimize conduction
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
9. Beam production & setup
Assemble an oven
• One vapour outlet
• Keep the window clean
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
10. Beam production & setup
Reduce doppler broadening
• Parallel velocity broadens the spectral line
• Pick out atoms with perpendicular velocity
• Doppler width estimated 19 MHz
Excitation laser
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
11. Beam production & setup
Eventual setup
• Frequency doubled tunable
Ti:S laser
• Atomic beam in vacuum:
2.3*10-7 mBar
• Observe fluorescence with
PMT
• Register wavelength with
ATOS LM007
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
12. Theory of spectroscopy
Overview – Zooming in on quantum mechanics
• Levels & Terms
• Isotope shifts
• Hyperfine splitting
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
13. Theory of spectroscopy
Levels & Terms
• Quantum numbers
– 3d64s2 5D4 3d64s4p 5D4
• Aufbau principle
– 2 electrons in every shell
– Distribution amongst shells
determines Terms
– Term symbols: 2s+1Lj
– Iron has 5D4 in the ground state
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
14. Theory of spectroscopy
Isotope Shifts
• Normal, Specific and Field shift
• Normal and specific shift
– Kinetic terms due to wobbling of the
nucleus
– Energy levels are influenced
– Effect: MS Z Z (M NMS M SMS )
Z Z
me
M NMS
mu
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
15. Theory of spectroscopy
Hyperfine splitting
• Caused by nuclear spin
• Charge circling the nuclear B-field
interacts as magnetic dipole
• New quantum number:
F I J
• Interaction energy:
A
E F ( F 1) J ( J 1) I ( I 1)
2
g s gi me
• Splitting of levels A Z 3 4 mec 2
3 Mp
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
16. Summary
• Evaporate iron to form a
beam
• Let the iron interact with the
excitation laser
• Quantum theory describes
this interaction
• Let’s analyse the
measurements !
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
17. Results Fraction Spin
54Fe 0.05845(35) 0
Isotopes 56Fe
57Fe
0.91754(36)
0.02119(10)
0
½
• Two isotopes easily 58Fe 0.00282(4) 0
found
• Intensity is directly
proportional to isotope
fraction
• Highest peaks
correspond to highest
fraction
• 57Fe and 58Fe remain
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
18. Results Fraction Spin
54Fe 0.05845(35) 0
56Fe 0.91754(36) 0
Isotopes 57Fe 0.02119(10) ½
•
58Fe
57Fe is split in four 0.00282(4) 0
– Summed relative intensities
should relate to isotope fraction
• 58Fe is very weak
– Should have the same
distance from 56Fe as 54Fe
Z Z
MS ( M NMS M SMS )
Z Z
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
21. Discussion
Hyperfine coupling constant
• Which peak corresponds to Ecg
which transition ?
– Longest arrow highest
frequency
– Clebsch-Gordan coefficients
• Can we be sure that A1 and A2
are both positive ?
– A1 should be positive*
2 2 1 EA
A1 E
2 5 2 1
A B
5 2 2 2 EC
1
E
5 2 5 2 1
ED
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
[*] Physical Review V148 #1 1966 – “Hyperfine interactions and the magnetic fields due to core polarization in Fe”, W.J. Childs, L.S.
Goodman
22. Discussion
Hyperfine coupling constant Method A1 A2 Ecg
• Options for matrix algebra +,cgc -24 24 511
+,-Ta 43 47 445
– Omission of rows / least +,-Td 47 43 447
squares +,L. sq 45 45 455
– Clebsch gordan / Manual -, cgc -24 -24 511
peak assignment -, -Tb 47 43 424
– Sign of second coupling -, -Tc 43 47 424
constant -, l. sq 45 45 428
• None gives the expected
result 2 2 1 EA
A1 E
2 5 2 1
A B
– Values are in the order of 5 2 2 2 EC
1
E
the literature values* 5 2 5 2 1
ED
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
[*] J. Phys. B: At. Mol. Opt. Phys. 30 (1997) 5359–5365Optical isotope shifts in the iron atom - Bentony, Cochrane and Griffith
23. Conclusion
• Fe Atomic beam production is possible
– Oven can be improved to lengthen sample lifetime
• Isotope splitting has been resolved
• Hyperfine splitting has not been resolved
– One more peak is needed to solve the system exactly
– Excitation laser needs stability improvements
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion