Pomeranchuk cooling to millikelvin temperature without forming bulk solid 3He

It has been found that the formation of bulk solid 3He during Pomeranchuk cooling can be suppressed when large quantities of activated charcoal are included in the cell. Adiabatic compressional cooling experiments were performed reaching temperatures as low as 1 mK with a cell which contained 2.2 g of activated charcoal, in addition to the 14 cm3 of 3He. The absence of bulk solid 3He was demonstrated by measuring time constants for a powdered CMN magnetic thermometer with respect to the pressure on the melting curve. It is hypothesized that the enormous surface area of the charcoal allows the solid 3He to develop in a several monolayer thick, surface structure. 2 figures