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