E. L. Hahn.
  <b>Spin echoes</b>.
  <i>Phys. Rev.</i>, 80:580, 1950.
  <A HREF="http://vis.cs.brown.edu/results/bibtex/Hahn-1950-SES.bib">(bibtex:
  Hahn-1950-SES)</A>.<br />