a CdS crystal annealed in an inert atmosphere at a temperature and for a period of time to provide substantially maximum acoustic attenuation at {TAIL ~ the operating frequency} of {HEAD ~ the crystal}; and 
a CdS crystal annealed in an inert atmosphere at a temperature and for a period of time to provide substantially maximum acoustic attenuation at { TAIL ~ the operating frequency } of { HEAD ~ the crystal } ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH