Bachelors Thesis Presentation
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Transcript of Bachelors Thesis Presentation
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
Overview• Motivation – Why spectroscopy on Iron ?• Atomic beam production and setup• Theory of spectroscopy• Results
– Resolving isotopes• Discussion
– Resolving hyperfine splitting• Conclusion• Debate
Introduction• Shifting constant results in
renewed interest in spectroscopy1,2
• Iron is a suitable element: – High universal abundance – High mass number, Z=56
• 4 3 ( )hfE Z g S I
[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,
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
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 theVapor Pressure of Iron from 1573 K to 1973 KFrank T. Ferguson, Joseph A. Nuth, and Natasha M. JohnsonJ. Chem. Eng. Data, 2004, 49 (3), 497-501 • DOI: 10.1021/je034152w
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
Beam production & setup1. Fix the sample (iron curls)2. Heat the sample3. Contain the heat4. Minimise speed distribution
(Doppler width)
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
Beam production & setupFixing 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
Beam production & setupHeating 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
Beam production & setupContaining the heat• Reflect IR radiation back to sample• Minimize conduction
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
Beam production & setupAssemble an oven• One vapour outlet• Keep the window clean
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
Beam production & setupReduce 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
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
Beam production & setup
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
Overview – Zooming in on quantum mechanics• Levels & Terms• Isotope shifts• Hyperfine splitting
Theory of spectroscopy
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
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
Theory of spectroscopy
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
Theory of spectroscopyIsotope Shifts• Normal, Specific and Field shift• Normal and specific shift
– Kinetic terms due to wobbling of the nucleus
– Energy levels are influenced
– Effect: ( )MS NMS SMSZ Z M MZ Z
eNMS
u
mM
m
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
( 1) ( 1) ( 1)2AE F F J J I I
Hyperfine splitting• Caused by nuclear spin• Charge circling the nuclear B-field
interacts as magnetic dipole• New quantum number:
• Interaction energy:
• Splitting of levels
Theory of spectroscopy
F I J
( 1) ( 1) ( 1)2AE F F J J I I ( 1) ( 1) ( 1)2AE F F J J I I
3 4 2
3s i e
ep
g g mA Z m cM
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
• Evaporate iron to form a beam
• Let the iron interact with the excitation laser
• Quantum theory describes this interaction
• Let’s analyse the measurements !
Summary
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
ResultsIsotopes• Two isotopes easily
found• Intensity is directly
proportional to isotope fraction
• Highest peaks correspond to highest fraction
• 57Fe and 58Fe remain
Fraction Spin
54Fe 0.05845(35) 056Fe 0.91754(36) 057Fe 0.02119(10) ½ 58Fe 0.00282(4) 0
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
ResultsIsotopes• 57Fe is split in four
– Summed relative intensities should relate to isotope fraction
• 58Fe is very weak– Should have the same distance
from 56Fe as 54Fe
Fraction Spin
54Fe 0.05845(35) 056Fe 0.91754(36) 057Fe 0.02119(10) ½ 58Fe 0.00282(4) 0
( )MS NMS SMSZ Z M MZ Z
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
Peak Isotope Position Distance Width
1 54Fe -769 - 14.3
2 56Fe 0 769 14.3
3 57Fe 243 244 12.9
4 57Fe 455 212 18.2
5 57Fe 648 193 40.7
6 58Fe 735 86 32.1
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
DiscussionHyperfine coupling constant
•
2 12 ( )A cgE E A A
2 15 2 2B cgE E A A
1 25 2 2C cgE E A A
1 25 2 ( )D cgE E A A
( 1) ( 1) ( 1)2AE F F J J I I
cgE
1
2
2 2 12 5 2 1
5 2 2 15 2 5 2 1
A
B
C
D
EA
EA
EE
E
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
DiscussionHyperfine coupling constant• Which peak corresponds to
which transition ?– Longest arrow highest
frequency– Clebsch-Gordan coefficients
• Can we be sure that A1 and A2 are both positive ?– A1 should be positive*
cgE
1
2
2 2 12 5 2 1
5 2 2 15 2 5 2 1
A
B
C
D
EA
EA
EE
E
[*] Physical Review V148 #1 1966 – “Hyperfine interactions and the magnetic fields due to core polarization in Fe”, W.J. Childs, L.S. Goodman
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
DiscussionHyperfine coupling constant• Options for matrix algebra
– Omission of rows / least squares
– Clebsch gordan / Manual peak assignment
– Sign of second coupling constant
• None gives the expected result– Values are in the order of
the literature values*
Method A1 A2 Ecg
+,cgc -24 24 511
+,-Ta 43 47 445
+,-Td 47 43 447
+,L. sq 45 45 455
-, cgc -24 -24 511
-, -Tb 47 43 424
-, -Tc 43 47 424
-, l. sq 45 45 428
[*] J. Phys. B: At. Mol. Opt. Phys. 30 (1997) 5359–5365Optical isotope shifts in the iron atom - Bentony, Cochrane and Griffith
Introduction – Beam production – Spectroscopic Theory – Results – Discussion - Conclusion
1
2
2 2 12 5 2 1
5 2 2 15 2 5 2 1
A
B
C
D
EA
EA
EE
E
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
Debate