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