Cerium Magnesium Nitrate Temperature Scale from Nuclear Orientation

Systematic deviations were found below 0.003oK in the temperature dependence of nuclear orientation of Ce137m in cerous magnesium nitrate, using the temperature scale proposed by Daniels and Robinson. The temperature scale below O.OO6°K was redetermined using a new method: nuclear orientation. This has the advan!age over the l'-ray heating method of high sensitivity at the lowest temperature. The most striking resu1t.l~ :hat a v~l?e of liT of 520, rather than the previously accepted 324, is obtained by demagnetization from Imtlal condItions of 18.8 kG deg-1• The useful absolute temperature range is thus extended by at least 60% in liT. Auxiliary experiments on oriented Pm!44 gave similar results and provided independent con­ firmation both of the inadequacy of the old temperature scale and of the validity of the new one.