Method for calibrating germanium-resistance thermometers in cryostats between 0.4 degrees K and 4 degrees K involves extrapolating the specific heat of a simple metal to low temperatures. This method is used when a magnetic thermometer is not available

Culbert, H. V.

Sungaila, Z.

English

NASA Technical Reports Server

May 1969
	
Brief 69-10149 
•
ICY C
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YES
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the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Calibration of a Resistance Thermometer Down to 0.04'K 
The problem: 
To develop a method for calibrating resistance ther-
mometers between 0.4°K and 4°K. The temperature 
calibration of such thermometers below the He vapor 
pressure range is usually done by extrapolating the 
inverse temperature behavior of the magnetic sus-
ceptibility of an appropriate paramagnetic salt. How-
ever, the necessary equipment for measuring the mag-
netic temperature at such low temperatures is not 
readily available. 
The solution: 
By extrapolating the specific heat of a simple metal 
to low temperatures, a germanium-resistance ther-
mometer has been calibrated down to 0.4°K. This 
provides an accurate and convenient method for cali-
brating stable germanium-resistance thermometers in 
cryostats for specific heat measurements below the 
He vapor pressure range, where a magnetic ther-
mometer is not available. No other measuring equip-
ment inside or outside the cryostat is needed other 
than the equipment required to measure specific heat. 
Also, there are no corrections to be made to the tem-
peratures as directly calculated from the extrapolation. 
The calibration has been checked by measuring the 
specific heat of a 1965 Calorimetric Conference 
Standard Copper sample and a high purity silver 
sample. 
How it's done: 
The temperature dependence of the specific heat, 
C, of a nonmagnetic metal can be given as: 
C = y T + (YT 3 ;
if T .( e D / 100 (o is the Debye temperature at 0°K.) 
and there is no nuclear specific heat. if a charge of 
heat Q is put into such a thermally isolated metal 
sample, originally at T, , it will come to equilibrium at 
a temperautre T 1 , determined by the equation: 
Q ±f	 CpdT2(T- T)± 4(T-T). 
Thus the temperature T i can be calculated if Q, 
T 1 , ,, and a are known. In this experiment a and .y 
are determined by specific heat measurements above 
0.75°K, where He and 1-Ic' vapor pressures can be 
used to calibrate the thermometer. AQ is determined 
from the electrical power used to heat a resistor on 
the sample and the measured background heat leak to 
the sample. T r is known either because it has been 
determined by vapor pressure measurements or be-
cause it has already been determined by the extrapo-
lation of C.
	 - 
The detailed calibration procedure is available. 
The thermometer calibrated is a germanium-resist-
ance thermometer with a nominal resistance range of 
133 ohms at 4.2°K to 9,400 ohms at 0.4°K. The 
metal sample used for the calibration is a 99.999% 
pure platinum cylinder, one inch in diameter and 
three inches long. Spectrochemical analysis of the 
sample showed -.5ppjn of both silver and magnesium 
and 24ppm of sodium. Platinum was picked for its. 
large low-temperature heat capacity due mostly to the 
electronic specific heat. 
Notes: 
1. The information may be of interest to persons 
concerned with low temperature calorimetry. 
2. Reference: Additional details contained in Cryo-
genics 8, 386, 1968. 
Am	 (continued overleaf) 
This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son acting on behalf of the United States Government assumes any
liability resulting from the use of the information contained in this 
document, or warrants that the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19690000149 2020-03-16T17:57:25+00:00Z
3. Inquiries may be directed to: 
Office of industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B69-10149 
Source: H. V. Culbert and Z. Sungaila
Solid State Science Division
(ARG-10318)
The problem: 
Inquiries concerning rights for commercial use of 
this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439
. 
Brief 69-10149	 Category 01


Calibration of a resistance thermometer down to 0.04 degrees K

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