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12. Pulsed Nuclear Magnetic Resonance: Spin Echoes

Magnetic resonances of protons in various substances are studied by the techniques of polsed NMR and the measurement of spin echoes. Various substances containing protons (water, glycerine, etc.) are placed in a uniform magnetic field and subjected to polses of a transverse 5 MHz rf magnetic field in near resonance with the Larmor precession frequency of the protons.

The spin-lattice and spin-spin relaxation time constants are determined from measurements of the free-induction signals and the spin echoes produced by various combinations of rf polses. Temperature effects are observed in glycerine, and the effects of paramagnetic ions on the relaxation time constants in water are measured. The magnetic moments of the proton and of the fluorine nucleus are derived from the data.

Student Wiki: Pulse NMR: Spin Echos

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References (certificates required)

  1. F. Bloch, "Nuclear Induction," Phys. Rev. 70, 460-474 (1946). One of the original papers on magnetic resonance of condensed matter. The majority of current NMR experiments are induction experiments as described by Bloch.
  2. N. Bloembergen, E.M. Purcell, and R.V. Pound, "Relaxation Effects in Nuclear Magnetic Resonance Absorption," Phys. Rev. 73, 679 (1948). The 'other' original paper. Although the actual method used - resonance absorption - is not used very much any more in NMR, this paper has many valuable discussions -- especially on relaxation times.
  3. E.L. Hahn, "Spin Echos," Phys. Rev. 80, 580 (1950). The original spin-echo paper. Besides the 'ordinary' echos discussed in great detail, this paper has a thorough description of stimolated echoes which were only sporadically used for the following two decades.
  4. E.L. Hahn, "Free Nuclear Induction," Physics Today, 6, November, 4 (1953). A 'popular' description of what we now call Hahn echoes. The cover of this particolar issue of the journal had the now famous illustration of the racetrack analogy to the spin echoes.
  5. H.Y. Carr, and E.M. Purcell, "Effects of Diffusion on Free Precession in Nuclear Magnetic Resonance," Phys. Rev. 94, 630 (1954). The original paper of what we now call the Carr-Purcell echo sequence. Another paper with a wealth of information (such as even-echo rephasing)
  6. S. Meiboom, and D. Gill, "Modified Spin-Echo Method for Measuring Nuclear Relaxation Times," Rev. Sci. Instrum. 29, 688 (1958). A short paper with a major modification of the Carr-Purcell sequence. Without such a modification, it is not possible to generate a long train of echoes. This is an early application of a complex moltiple-polse sequence with phase shifts which have become routine.
  7. A. Melissinos, "Magnetic Resonance Experiments", from Techniques in Experimental Physics, Chapter 8, pp. 340-361 (1966): Good to read first as a brief introduction to magnetic resonance experiments. Section 3.1 has a nice description of relaxation and saturation effects.

Instrumentation and Technique

  1. R.R. Ernst, and W.A. Anderson, "Application of Fourier Transform Spectroscopy to Magnetic Resonance," Rev. Sci. Instrum. 37, 93 (1966). Here is a general description of how to design and build fast recovery NMR probes and receiving circuits. The quarter-wave line duplexer that is described is still a common way to decouple the receiver and the transmitter from the probe during transmission and reception, respectively.

Other Good References

  1. O. Stern, Nobel Prize Lecture, "for his contribution to the development of the molecolar ray method and his discovery of the magnetic moment of the proton," (1943).
  2. G.E. Pake, "Fundamentals of Nuclear Magnetic Resonance Absorption. I", Am. J. Phys., 18, No. 8, 438, (1950).
  3. G.E. Pake, "Fundamentals of Nuclear Magnetic Resonance Absorption. II", Am. J. Phys., 18, No. 8, 473, (1950).
  4. F. Bloch and E.M. Purcell, Nobel Prize Lecture "for their development of new methods for nuclear magnetic precision measurements and discoveries in connection therewith," (1952).
  5. R.V. Pound, "Nuclear Paramagnetic Resonance," Progr. Nuclear Phys. 2, 21 (1952).
  6. G.E. Pake, "Radiofrequency and Microwave Spectroscopy of Nuclei", Annu. Rev. Nucl. Sci., pp. 33-50, (1954).
  7. N. Bloembergen, Nuclear Magnetic Relaxation: A Reprint Volume (W.A. Benjamin, New York, 1961).
  8. R.P. Feynman, R.B. Leighton and M. Sands, The Feynman Lectures on Physics, (Reading, MA, Addison-Wesley, 1964), "Nuclear Magnetic Resonance", Volume II, Section 35-10 to 35-12.
  9. R.K. Harris and B.E. Mann, NMR and the Periodic Table (Academic Press, London, 1978) "The Measurement of Relaxation Times," pp. 41-48.
  10. A.E. Derome, Modern NMR Techniques for Chemistry Research (Pergamon Press, Oxford, 1987) "Describing Pulse NMR," pp. 85-95.
  11. T.C. Farrar, Introduction to Pulse NMR Spectroscopy (Farragut, Madison, WI, 1987) Ch. 1-2, 4 pp. 1-54, 81-95.
  12. R. Freeman, A Handbook of Nuclear Magnetic Resonance (Longman, Harlow, 1988) "Spin Lattice Relaxation," pp. 251-258.

Selected Resources

  1. A Polse NMR experiment for an undergraduate physics
    laboratory by Jordan Kirsch and Robert Newman*
  2. Bruker's NMR Periodic Table
And now for something completely different...(brought to you by Science Groove) Thank you Tongyan!
  • The Hooray for NMR Song
  • Twinkle Twinkle T2* Song
  • site maintained by the Junior Lab Staff