A technique for cooling single crystals below 90 K for x-ray diffraction

An efficient and inexpensive method of cooling a crystal to low temperatures and maintaining fine temperature control (±0·5 degC) at the crystal has been developed for single crystal x-ray diffraction investigations. Temperature control is attained by using a float and microswitch mechanism to maintain a virtually constant liquid level (±5 mm) in the boil-off chamber and by using a slow gravity fill procedure to reduce any pressure variations in the gas stream. The apparatus features a small Dewar which allows for ready use on either precession or Weissenberg cameras or with counter diffractometers. Operation at sustained temperatures at approximately 90 K requires less than 20 1 of liquid nitrogen per day.