Cryostat for Neutron Diffraction Studies Between Liquid Helium Temperatures and Room Temperature

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Abstract
An efficient all metal cryostat is described for temperature dependent neutron diffraction studies in the range of liquid helium temperatures to room temperature. A modification of the Swenson type heat exchanger is employed in which the temperature is controlled by regulating the flow of cold gas or liquid through the exchanger by means of a precision needle valve. Using liquid helium in the system, sample temperatures in the range 2 to 100°K can be obtained. For fixed settings of the needle valve in the range for 4.2 to 40°K, the long term temperature drifts are less than 0.01°K/h. The short term periodic fluctuations are on the order of ±0.1°K or less. On one filling of liquid helium, the sample can be maintained for 2 days at any given temperature from just above the boiling point of helium up to about 100°K with an average loss rate of 25 cc of liquid per hour. The loss rate increases to about 45 cc/h when the sample is held at 4.2°K. Using liquid nitrogen in place of liquid helium in the temperature control system, sample temperatures between 77°K and room temperature may be obtained.