Mossbauer Effect In Fe-57 At Very Low Temperatures

The preparation of a 10 mc Co/sup 57/ source in natural iron metal is described. The source was placed in an adiabatlc demagnetization cryostat fitted with thin windows of Mylar plastic and Beryllium metal. The 14.4-kev radiation was filtered by an oscillating resonant absorber of approximately 2 mg/cm/sup 2/ Fe/sup 57/ plated on a 0.1 mil nickel foil. Intensities were measured alternately in each direction over the same length of absorber travel. The absorption coefficients were examined by measuring the resonant gamma -ray transmission from the source at room temperature by the technique of Doppler- shifting the source relative to the cold absorber. Larger asymmetries are produced by cooling the source instead of the absorber, due to the magnetic moment difference between Co/sup 57/ and ground-state Fe/sup 57/. Calculations were made which predicted a larger over-all effect than the scheme of cooling an absorber; accordingly, the experiment was conducted using a cold source and absorber at room temperature. (B.O.G.)