Cam-Driven, Constant-Acceleration Mössbauer Spectrometer

Abstract

Mössbauer spectroscopy relies on the first-order relativistic energy shift (ΔE = v/c Eγ) to produce a small (approx. 1:10¹⁰ to 1:10¹⁴) energy shift in gamma-ray energy, thereby destroying the condition for resonant absorption. For the recoilless radiation emitted by Fes^57m and Sn^119m, the maximum velocity needed for the study of isomer shift, quadrupole spiittings, and magnetic hyperfine structure is of the order of 1 cm/sec. In general, two types of spectrometers have been used—constant velocity and constant acceleration. The constant-velocity spectrometer, such as constructed from a lathe motion, receives data at one velocity and then is reset to obtain data at a new velocity. Usually each velocity is sampled only once or at most a few times during a run, and any instrumental drifts (detector high voltage, amplifier gain, etc.) or decay of the source will be reflected in the data. For these reasons, constant-velocity spectrometers are usually restricted to cases involving small changes in line shape.

Supported by the National Science Foundation and by the Advanced Research Projects Agency through the Materials Science Center of Cornell University.

On leave at the Department of Chemistry, First College, The University of California, San Diego, La Jolla, California.