Postprint version. Published in Chemical Mossbauer Spectroscopy, Volume 1, January 1, 1984, pages 113-132. Copyright © 1984 Springer. The original publication is available at http://www.springer.com/?SGWID=0-102-0-0-0.
NOTE: At the time of publication, the author R.B. Frankel was not yet affiliated with Cal Poly.