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Bachelors Thesis Presentation

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This presentation describes my research on a hyperfine transition within the iron atom, using a laser setup for evaporating iron and measuring its spectrum.

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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  • 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
  • 19. 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
  • 20. Discussion Hyperfine coupling constant • E  A F ( F  1)  J ( J  1)  I ( I  1) 2 EA  Ecg  2  ( A2  A1 ) EB  Ecg  5 2 A2  2 A1 EC  Ecg  5 2  A1  2 A2 Ecg ED  Ecg  5 2  ( A1  A2 )  2 2 1  EA     A1   E   2 5 2 1     A2    B  5 2 2 1   EC     E      5 2 5 2 1  ED  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
  • 24. Debate