Among the isotopes used in Mossbauer spectroscopy (MS), 67Zn has the highest energy resolution (5 x 10-16 ) and an extreme sensitivity for the measurements of hyperfine interactions, to determine the electric field gradient (EFG) tensor and internal magnetic field at the nucleus. The distribution of charges between lattice sites can then be calculated from the EFG. Since 67Cu is a source for 67Zn MS, the technique has been used to study high Tc superconductors. With the use of emission MS, the superconductor is doped with 67Cu, and it is known precisely where the 67Zn daughter is formed in the crystal structure. The difficulty in obtaining 67Zn spectra, with line widths of 0.31 microns/sec, and the poor signal/noise, has limited the use of this technique to a few laboratories. A new type Mossbauer Spectrometer is needed and has been designed based on an experiment by Grodzins and Phillips. Rather than moving a source or absorber, as has been done with a conventional Doppler velocity modulation spectrometer, the optical ((-ray) path is changed as a function of time. This is achieved by moving a plastic wedge, or a plastic wheel at an angle to the drive shaft in the (-ray beam. For 67Zn, a shift of one line width corresponds to a rotation of 100 RPM. In this technique, the source and the absorber can be rigidly mounted together and virtually eliminate any vibrational noise. The signal to noise in MS can be greatly improved with the use of a resonant detector. These detectors have been developed for 57Fe, 119Sn and 151Eu. 67Zn is an ideal candidate. Resonant detectors make use of the conversion electrons that compete with the (-ray emission after the resonant absorption. The conversion electrons are detected by an organic plastic scintillator filled with a 67Zn enriched inorganic absorber placed in contact with a photomultiplier. The only significant noise parameter is the photoelectric effect, but for Zn this cross section is 103 times smaller. Even with a recoil free fraction of only 2%, the net gain is a factor of 20.
