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He3 cryostat for steady state nuclear magnetic resonance measurements in metals Puls, Manfred Paul

Abstract

A He³ cryostat was designed for steady state nuclear magnetic resonance measurements. The cryostat required about one liter of He³ at NTP. This amount of He³ was liquified at 1.2°K, which was the temperature of the surrounding liquid He⁴ bath, and then pumped on by means of a four-stage mercury diffusion pump. By this procedure, a liquid He³ temperature of 0.35 K was achieved and maintained for four hours. The r-f coil and sample were in direct contact with the liquid He³ to ensure sufficient heat transfer between the two. The temperature of the liquid He³ was measured by means of vapour pressure measurements of the evaporating He³ and by means of resistance measurements of a carbon resistance in contact with the liquid He³. The system was non-recirculating, since a total, uninterrupted run of four hours was considered long enough for most experiments. The He³ could also be retransferred within 20 minutes after such a run, and this process could be continued until in-sufficient quantities of liquid He⁴remained to cool the surroundings.

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