I= LASER ASSISTED ISOTOPIC STUDIES USING TIME OF FLIGHT MASS SPECTROMETER
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Title of Thesis
LASER ASSISTED ISOTOPIC STUDIES USING TIME OF FLIGHT MASS SPECTROMETER

Author(s)
Muhammad Saleem
Institute/University/Department Details
Department of Physics/ Quaid-i-Azam University Islamabad
Session
2006
Subject
Physics
Number of Pages
91
Keywords (Extracted from title, table of contents and abstract of thesis)
isotopic studies, lithium isotopes, isotope separation, photoionization, hyperfine structure, gaussian bean, time of flight mass spectrometer system, laser atom interaction, hyperfine structure, laser system

Abstract
The present work is devoted to the spectroscopic studies of the lithium isotopes using a locally designed and fabricated atomic beam - Time of Flight mass spectrometer system. Different intermediate states 2p 2P1/2, 3/2, 3s 2S, 3p 2p, 3d 2D, 4s 2S, 4p 2p and 4d 2D of lithium have been exploited for the isotope separation. The proposed method enabled the isotope separation even if the isotopes have not been selectively excited. Fine structure in the 2p excited state for both the isotopes Li6 and Li7 has been resolved for the first time using this new technique. It is also noticed that the much higher energy density of the exciter laser limits the resolution of the fine structure levels of the lithium isotopes that leads to a loss in the enrichment of Li6 due to the power broadening effect. We have investigated the yield of Li6 exploiting the above mentioned excited states. An efficient pathway for the quantitative enrichment of the Li6 isotope by tuning the exciter laser at the 3p 2p1/2,3/2 state of Li6 have also been proposed in which a concentration up to 60 % is demonstrated from a natural isotopic abundant lithium sample.

In addition, we proposed an alternate technique for the simultaneous measurement of photo ionization cross section of the excited states of the isotopes and their corresponding number densities. We report extensive new measurements of the photo ionization cross section of the above mentioned excited states. By varying the frequency of the ionizer laser, different regions of the continuum have been investigated and a decreasing behavior of the photo ionization cross section by increasing the energy of the ionizer laser is reported experimentally for the first time. The photoionization cross section from the 2p 2pl/2,3/2, 3p 2p, 4p 2p, 3d 2D and 4d 2D excited states of the lithium isotopes is maximum near the ionization threshold and a smooth decrease in the cross section is observed for the excess energy above threshold. However, for the 3s 2S and 4s 2S excited states, the cross section of the photoionization is lower at threshold and then increases to a maximum value and then decreases. It is also observed that the decrease in the cross section of the 3d 2D and 4d 2D excited states is more hydrogenic than that of the 2p 2P1/2,3/2, 3p 2p, and 4p 2p excited states and for the 3s 2S and 4s 2S excited states, it is purely non- hydrogenic.

Download Full Thesis
2652.33 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
355.53 KB
2 1 Introduction 1
348.42 KB
  1.1 Overview 1
  1.2 Laser Atom Interaction 2
  1.3 Fine Structure Levels 7
  1.4 Hyperfine Structure And Isotopic Shift 8
  1.5 Photoionization Cross Section 9
  1.6 Gaussian Bean 10
  1.7 Layout Of Thesis 12
3 2 Experimental Setup 13
238.71 KB
  2.1 Laser System 14
  2.2 Data Acquisition System 18
  3 Design And Fabrication Atomic Beam Apparatus And Time Of Flight Mass Spectrometer 20
  3.1 Atomic Beam Apparatus 20
  3.2 Time Of Flight Mass Spectrometer 24
  4 Laser Isotope Separation Of Lithium 33
  4.1 Ionization Yield Of Both The Lithium Isotopes From The 2p 2 p 1/2 , 2 /3 Excited State 33
  4.2 Ionization Yield From The 3s 2 s, 3p 2 p. 3d 2 d, 4s 2 s, 4p 2 p And 4d 2 d Excited States Of Lithium Isotopes 40
4 5 Simultaneous Measurements Of The Photoionization Cross Section Of The Lithium Isotopes 50
788.01 KB
5 6 Conclusion 83
60.86 KB
6 7 References 85
198.74 KB