Mössbauer Spectroscopy of Iron

In this experiment students are introduced to the beautiful physics of the Mössbauer effect which allows for energy resolutions of ~ a part in 1013. The effect is used to measure the intrinsic magnetic field inside iron crystals and to measure the nuclear quadrupole splitting in crystals with electric field gradients at sites of iron nuclei. The effect is also used to measure the subtle "chemical" shift due to the different electronic environments of the iron nuclei in the source and absorber. Finally, relativistic effects can be observed by cooling the absorber to the temperature of liquid nitrogen, 77K, with the source remaining at room temperature. Cooling the absorber relative to the source causes radiation from the source to be red shifted as observed by the absorber, thus changing the amount of first order Doppler shift needed to observe a particular resonance.

Experiment & background information

Discussion Questions

Describe what would happen to the data set for enriched iron if each of the following changes in the setup were made, assuming that all other settings remain the same.

  1. The gain on the pulse height amplifier (Ortec 575A) is increased.
  2. The high voltage bias on the detector is changed from +1800V to +1500V.
  3. The lower-level discriminator is reduced to zero.
  4. The MCS dwell time is changed from 500 microseconds to 250 microseconds.
  5. The phase setting on the function generator is changed from -090 to 000.