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Low temperature specific heat of plutonium
Low Temperature Specific Heat of Plutonium WE have measured the specific heat at low temperatures of a sample of high purity (less than 80 p.p.m. total impurity) plutonium metal in the ~t-phase. The sample was enclosed in a copper calorimeter which could be kept in mechanical contact with an evacuated outer container kept at the temperature of liquid helium. On breaking this contact, the temperature of the calorimeter began to rise owing to the radioactive self-heat developed by the plutonium sample. Interposed between the calorimeter and the container was a radiation shield whose temperature was controlled by a servomechanism and followed that of the calorimeter within 10-2 degrees. Temperatures were measured with thermocouples of a dilute cobalt alloy in gold vs copper. Between our lowest temperature, 12-5 ° K, and 80 ° K the correction for Co - Cv is small and permits analysis of our data. From this we obtain a value of the Debye characteristic temperature 0D of between 155 and 160, except for a rather narrow temperature range centred around 60 ° K where it drops to about 147. This leads to a value for the electronic specific heat of about 3 x 10-3 cal/mole, deg 2, which is a little higher than the value for uranium. Our results differ in three essential features from those published by Sandenaw. ~ We have failed to reproduce the striking anomaly found by him near 20 ° K where our data are quite smooth. Neither could we confirm the maximum observed by him near 60 ° K where we have only noticed the slight fall in 0D mentioned above. Finally, our analysis leads to a value of the electronic specific heat ten times lower than that given by Sandenaw. These results are in good agreement with unpublished work by J. C. Taylor ofA.W.R.E., Aldermaston. A more detailed analysis of these data and those above 80 ° K will be published later.
A.E.R.E., Harwell, Berks, U.K.
J. A. LEE
Clarendon Laboratory, OaJbrd, U.K.
K . MENDELSSOHN
P. W. SUTCLIFFE
(3 July 1965) REFERENCE 1. SANDENAW,T.
A. J. Phys. Chem. Solids 23, 1241 (1962)
The Electrical Resistivity of ~-Manganese between 2 and 325 ° K WE report here the results measurements that we have electrical resistivity of high temperatures between 2 and C R Y O G E N I C S . A U G U S T 1965
of some very precise recently made on the purity ~-manganese at 325 ° K. The material
from which we fabricated our specimens had been made electrolytically and was supplied by KochLight Laboratories Ltd. Its purity was given as 99.995 per cent with respect to spectrographically detectable impurities and these were specifically named as magnesium 20 p.p.m., silicon 2 p.p.m., copper less than I p.p.m., and iron and sulphur zero (no others being mentioned). ~t-Manganese is a very brittle metal which by ordinary standards is ditticult to fabricate into Table 1. The electrical resistivity of ~-manganese at various selected temperatures
Temperature Res~tivi~ (°K) (~Qcm) 0 4-2 10 20 30 40 50 60 70
6"9 9 19 54 92 118 128 132 133
Temperature Res~tivi~ (°K) (v~cm) 80 90 100 150 200 250 273"15 295 325
132-5 132 132"5 137 140"5 143 143"5 144"0 145-2
specimens of regular shape and accurately known form-factor. However, the metal proved to be amenable to cutting by means of spark erosion and a large number of specimens were produced. The specimen to which the data of Figure 1 and Table 1 relate had a length of 24.95 mm and a rectangular cross-section of width 4-92 mm and thickness 0.965 mm. The error in the resistivity data associated with the formfactor did not exceed I per cent. As the electrical resistivity of ~t-manganese is very susceptible to the presence of adsorbed hydrogen, 1 the specimens, after reduction in dilute hydrochloric acid to remove surface contamination, were annealed under a vacuum of 10-6 to 8 x 10-6 torr for 7 hr at 625 ° C. After this treatment the resistivity at 295 ° K was 144.0 laf~cm ( + 1 per cent), and the estimated resistivity at 0 ° K COo), obtained by extrapolating from the region of 2 ° K, was found to be 6.9 laf~cm. The previous best work on the absolute resistivity had been done by White and Woods,l, z but these workers encountered the fabrication and impurity problems mentioned above and gave the much less satisfactory figures of p29s = 155 and po = I 1.3 laflcm with error limits of + 20 per cent for the best of their three samples and ,0295 = 154 and po = 16.8 laf~cm ( + 2 0 per cent) for a second sample. Referring now to Figure 1, it will be observed that on cooling from 325 ° K the resistivity falls only very slowly at first until at 94 ° K a minimum is reached (131.9 laflcm). This is at or very close to the 227
A.E.R.E., Harwell, Berks, U.K.
J. A. LEE
Clarendon Laboratory, OaJbrd, U.K.
K . MENDELSSOHN
P. W. SUTCLIFFE
(3 July 1965) REFERENCE 1. SANDENAW,T.
A. J. Phys. Chem. Solids 23, 1241 (1962)
The Electrical Resistivity of ~-Manganese between 2 and 325 ° K WE report here the results measurements that we have electrical resistivity of high temperatures between 2 and C R Y O G E N I C S . A U G U S T 1965
of some very precise recently made on the purity ~-manganese at 325 ° K. The material
from which we fabricated our specimens had been made electrolytically and was supplied by KochLight Laboratories Ltd. Its purity was given as 99.995 per cent with respect to spectrographically detectable impurities and these were specifically named as magnesium 20 p.p.m., silicon 2 p.p.m., copper less than I p.p.m., and iron and sulphur zero (no others being mentioned). ~t-Manganese is a very brittle metal which by ordinary standards is ditticult to fabricate into Table 1. The electrical resistivity of ~-manganese at various selected temperatures
Temperature Res~tivi~ (°K) (~Qcm) 0 4-2 10 20 30 40 50 60 70
6"9 9 19 54 92 118 128 132 133
Temperature Res~tivi~ (°K) (v~cm) 80 90 100 150 200 250 273"15 295 325
132-5 132 132"5 137 140"5 143 143"5 144"0 145-2
specimens of regular shape and accurately known form-factor. However, the metal proved to be amenable to cutting by means of spark erosion and a large number of specimens were produced. The specimen to which the data of Figure 1 and Table 1 relate had a length of 24.95 mm and a rectangular cross-section of width 4-92 mm and thickness 0.965 mm. The error in the resistivity data associated with the formfactor did not exceed I per cent. As the electrical resistivity of ~t-manganese is very susceptible to the presence of adsorbed hydrogen, 1 the specimens, after reduction in dilute hydrochloric acid to remove surface contamination, were annealed under a vacuum of 10-6 to 8 x 10-6 torr for 7 hr at 625 ° C. After this treatment the resistivity at 295 ° K was 144.0 laf~cm ( + 1 per cent), and the estimated resistivity at 0 ° K COo), obtained by extrapolating from the region of 2 ° K, was found to be 6.9 laf~cm. The previous best work on the absolute resistivity had been done by White and Woods,l, z but these workers encountered the fabrication and impurity problems mentioned above and gave the much less satisfactory figures of p29s = 155 and po = I 1.3 laflcm with error limits of + 20 per cent for the best of their three samples and ,0295 = 154 and po = 16.8 laf~cm ( + 2 0 per cent) for a second sample. Referring now to Figure 1, it will be observed that on cooling from 325 ° K the resistivity falls only very slowly at first until at 94 ° K a minimum is reached (131.9 laflcm). This is at or very close to the 227