The Helsinki temperature scale, used earlier in measurements of the heat capacity of liquid 3He (1-10 mK), is compared with the National Bureau of Standards (NBS) noise and nuclear-orientation temperature scale. The superfluid transition temperature (Tc) of 3He at zero pressure and the superconductive transition temperatures of tungsten and beryllium were used as fixed points. Tc on the NBS scale was found to be 1.025 ± 0.02 mK, in close agreement with the Helsinki value 1.04 mK. The results support the Helsinki data on the heat capacity of 3He.Peer reviewe

Lhota, E.

Manninen, M. T.

Pekola, Jukka P.

Soinne, A. T.

Soulen, R. J.

Physical Review Letters

Aaltodoc Publication Archive

This is an electronic reprint of the original article.This reprint may differ from the original in pagination and typographic detail.Author(s): Lhota, E. & Manninen, M. T. & Pekola, Jukka & Soinne, A. T. &Soulen, R. J.Title: Comparison of the National Bureau of Standards and the HelsinkiTemperature Scales and its Effect on the Heat Capacity of Liquid 3Hebelow 10 mKYear: 1981Version: Final published versionPlease cite the original version:Lhota, E. & Manninen, M. T. & Pekola, Jukka & Soinne, A. T. & Soulen, R. J. 1981.Comparison of the National Bureau of Standards and the Helsinki Temperature Scalesand its Effect on the Heat Capacity of Liquid 3He below 10 mK. Physical Review Letters.Volume 47, Issue 8. P. 590-592. ISSN 0031-9007 (printed). DOI:10.1103/physrevlett.47.590.Rights: © 1981 American Physical Society (APS). http://www.aps.org/All material supplied via Aaltodoc is protected by copyright and other intellectual property rights, andduplication or sale of all or part of any of the repository collections is not permitted, except that material maybe duplicated by you for your research use or educational purposes in electronic or print form. You mustobtain permission for any other use. Electronic or print copies may not be offered, whether for sale orotherwise to anyone who is not an authorised user.Powered by TCPDF (www.tcpdf.org)VOLUME 47, +UMBER 8 PHYSICAL REVIEW LETTERS 24 AU| US'I 1981Comparison of the National Bureau of Standards and the Helsinki TemperatureScales and its Effect on the Heat Capacity of Liquid 3He below 10 mKE. I hota, '& M. T. Manninen, J. P. Pekola, and A. T. SoinneLow TemPerature Laboratory, Helsinki University of Technology, SF-02150 EsPoo 15, EinlandandH. J. Soulen, Jr.National Bureau of standards, washington, D. C. 20234Q,eceived 1 April 1981)The Helsinki temperature scale, used earlier in measurements of the heat capacityof liquid He (1-10 mK), is compared with the National Bureau of Standards (NBS) noiseand nuclear-orientation temperature scale. The super fluid transition temperature (T, )of 3He at zero pressure and the superconductive transition temperatures of tungstenand beryllium were used as fixed points. T, on the NBS scale was found to be 1.025+ 0.02 mK, in close agreement with the Helsinki value 1.04 mK. The results supportthe Helsinki data on the heat capacity of 3He.PACS numbers: 67.50.Dg, 07.20.DtAn internationally accepted temperature scalein the low-millikelvin region has recently becomeimportant in connection with experiments on nor-mal and superfluid 'He. The effective mass pg*of 'He, inferred from the heat capacity data byAlvesalo stan ,' dev. iates about 30/0 from earlierresults' 4; the major cause of the discrepancycould be due to different temperature scales. Be-cause the important Fermi-liquid parameters aredependent on I*, it is essential to know the cor-rect specific heat.The temperature scales used in the variousheat capacity measurements cannot be compareddirectly. In the Helsinki experiment"' the tem-perature scale is fixed to the phase separationline between the normal and superfluid phases of'He, but measurements of Refs. 2 and 3 did notreach this line. An attempt to resolve the dis-crepancy has been made by Roach, Meisel, andEckstein, ' who have measured the volume deriva-tive of the heat capacity. Their conclusions areweak, however, because the experiment is alsosensitive to the temperature scale used and itdoes not give the heat capacities themselves.We report in this Letter measurements whichcheck directly the Helsinki temperature scale em-ployed in Ref. 1. The test was performed by com-paring this scale with the National Bureau of Stan-dards (NBS) cryogenic temperature scale, ' be-lieved to be accurate to + 0.5% and thus one of themost reliable scales in the low-millikelvin re-gion. The superconductive transitions of tung-sten and beryllium and the superfluid transitionof 'He at zero pressure were used as fixed pointsin the experiment. The heat capacity data of Al-vesalo et al."are strongly supported by our re-sults.The Helsinki scale is based on the assumptionthat the nuclear spin susceptibility of platinum isinversely proportional to T. The Curie constantwas found by measuring the spin-lattice relaxa-tion time ~, and by employing the Korringa rela-tion, 7,T =%=29.9 ms K. This value for the Kor-ringa constant K was measured by Ahonen, Krus-ius, and Paalanen' using a nuclear-orientationthermometer. The same platinum powder wasemployed in Refs. 1 and 8, as well as in the meas-urements reported here. The Helsinki scale isgiven as a set of (P, T) coordinates along thephase separation curve between normal and su-perfluid 'He. ' The absolute accuracy of the scale,+ 5/o, was estimated on the basis of knowledge onK and the precision of ~, measurements.The NBS-CTS-1 scale' was established by di-rectly intercomparing a Josephson junction noisethermometer and a nuclear-orientation thermom-eter between 10 and 50 mK and by employingnoise thermometry from 50 to 500 mK. Fromthe excellent agreement between the two thermom-eters the absolute accuracy of the NBS scale wasestimated as +0.5% below 50 mK. The scale canbe realized at other laboratories by means of cal-ibrated super conductive fixed points. 'In our experiments we used the superfluid tran-sition temperature T, of 'He at zero pressure(1.04 mK on the Helsinki scale) and the Curiesusceptibility of platinum to produce the Helsinkiscale. The superconductive transition tempera-tures of one pair of tungsten and beryllium sam-ples (15.60 and 23.59 mK on the NBS scale, re-590 1981 The American Physical SocietyVOLUME 47, NUMBER 8 PHYSICAL REVIEW LETTERS 24 AUGUST 1981spectively), immersed in He liquid, as well asthe transition temperatures of two other samplesof the same metals (15.50 and 23.02 mK on theNBS scale), mounted on the outside of the cell,were measured on the Helsinki scale.The experimental chamber, shown in Fig. 1,was thermally connected to the copper bundle ofa nuclear refrigerator. The platinum NMR coil,located in a cylindrical appendage to the mainchamber, was a compensated solenoid; the rf-field inhomogeneity at the platinum sample wasless than 5%%u&. The susceptibility of CLMN (ceri-um magnesium nitrate diluted to B%%u~ molar solu-tion by the corresponding lanthanum salt) wasused as a secondary thermometer. The coil as-semblies for the CLMN pill and the metal sam-ples were identical; the secondary coils wereconnected in series and coupled to a SQUID. Twoseparate inductance bridges, with different oper-ating frequencies, were employed for monitoringthe susceptibilities of CLMN and the supercon-ducting samples.The tungsten and beryllium samples outside thecell (not shown in Fig. 1) were bound with varnishand cotton thread to a bundle of copper wires,welded to a cylindrical copper block. A coil form,with primary and secondary coils, was pushedaround the samples and the spare copper wirethen folded back over the coils. This unit wasconnected through a copper rod to the silver sup-port of the 'He cell. The superconductive transi-tions of the outside samples were observed witha simple mutual inductance bridge. 'Because the superconductive transition temper-ature is very sensitive to magnetic fields, Earth' sfield was compensated with a solenoid outsidethe helium Dewar. Furthermore, the tungstenand beryllium specimens were protected with Mu-metal and superconducting niobium shields. Thiswas accomplished by enclosing the samples in-side the cell within three shields. The inner andouter ones were Mumetal and the middle one nio-bium. The samples outside the cell were shield-ed by a Mumetal can and a niobium cylinder.The residual magnetic field at the superconduct-ing samples inside the cell was determined bymeasuring the transition temperature as a func-tion of external static field produced by the pri-mary coil and by extrapolating linearly to zerofield. The flux change caused by the Meissnereffect was used as a measure of the magneticfield. The correction to be applied to the transi-tion temperature turned out to be less than 1%.The residual field inside the shields of the out-side samples was estimated to be small.The calibration between the platinum and theAg SIDER~ ~ ~ % ~ ~ ~ ~ ~I ~ ~ ~ ~ ~I IQ~ ~1~ ~0I ~IJI0~ I— Pt SAHPLE~ NHR COILp- ME TAL ANDNb SHIELDSPRIMARY ANSECONDARYW AND BeSAHPLES~ ~0~ ~ ~~ ~4~ ~Ag CHAMBERNb SHIELDP RIMAR Y ANDSECONDARY COILSCLHN~ /a.(I:J~:i:::':).r.8gl jg/f[~ IJFIG. 1. Experimental cell.591VOLUME 47, NUMBER 8 PHYSICAL REVIEW LETTERS 24 AUGUST 1981TABLE I. Measured values of the superconductive transition temperatures on the NBS scaleand on the Helsinki scale. The absolute accuracy of the NBS values is + 0.1 mK and the preci-sion of the data measured on the Helsinki scale is + 1 jp.NBSscale(mK)Helsinki scale (mK)B = 28 mT B = 28 mT JS = 0 B = 28 mT 8 = 28 mTT, of 3He,NBS scale(mK)W inside 15.60W outside 15.50Be inside 23.59Be outside 23.0216.3115.6523.7323.0016.2915.9023.6622.9616.2915.8623.5422.9716.2923.6816.3023.601.001.021.041.04CLMN thermometers was made from 1 to 24 mK.The superfluid transition point of 'He was foundby means of the CLMN thermometer, with a pre-cision of 0.1%, as a change in the slope of thetemperature drift curve; this point was employedto fi.x the Curie constant of platinum. The tung-sten and beryllium transition temperatures wererecorded with both thermometers.In Table I we show the measured superconduc-tive transition temperatures from five differentruns on the Helsinki scale. The external magnet-ic field (outside the shields) was either zero or28 mT, the field employed for platinum NMR.The superfluid transition temperatures on theNBS scale were obtained by assuming that bothscales are proportional to the absolute tempera-ture and by multiplying the Helsinki T, = 1.04 mKby the ratio of the NBS and averaged Helsinkitransition temperatures for each superconductivesample.In our measurements the tungsten transition ismore precise because it is sharp and at a lowertemperature. The scatter in the data of the sam-ple outside the cell is possibly due to lack ofthermal equilibrium between the sample and thethermometers. The beryllium transition oc-curred in a temperature interval of about 0.5 mK,but the width of the main part of the transitionwas less than 0.1 mK.The values derived from the beryllium dataagree with the Helsinki results T, = 1.04 mK,whereas the data from tungsten inside and out-side the cell differ from this result by 4.5% and2%, respectively. Because the source of this dis-crepancy is not clear, we chose to take an aver-age of the last column in Table I, giving equalweight to all of the samples. In this manner wefind T, = 1.025+ 0.02 mK for the superfluid transi-tion temperature of 'He at zero pressure on theNBS scale. The difference from the Helsinki val-ue is 1.4%, i.e. , of the same order as the errorlimits of this experiment.In summary we find that the Helsinki scale,with T, = 1.04 mK, agrees well with the NBSscale. This implies that the Korringa constantfor our platinum sample, K = 29.9 ms K, on whichthe Helsinki scale is based, is quite correct.The consistency of the two scales demonstratesthat an accurate temperature scale in the milli-kelvin region can be established by using the nu-clear Curie susceptibility of platinum, with thesuperfluid transition temperature of 'He employedas a fixed point. Our results also clearly showthat the heat capacity data of Alvesalo et al. ' donot suffer from significant errors traceable tothe Helsinki temperature scale.We are grateful to O. V. Lounasmaa for helpfulcomments and discussion. This work was finan-cially supported by the Academy of Finland.(a)Permanent address: Research Institute of Elec-trical Engineering, 25097 Praha 9, Bechovice, Czech-oslovakia.'T. A. Alvesalo, T. Haavasoja, M. T. M~~ninen, andA. T. Soinne, Phys. Rev. Lett. 44, 1076 (1980).2W. R. Abel, A. C. Anderson, W. C. Black, and J. C.Wheatley, Phys. Rev. 147, 111 (1966).A. C. Mota, R. P. Platzeck, R. Rapp, and J. C.Wheatley, Phys. Rev. 177, 266 (1969).J. C. Wheatley, Rev. Mod. Phys. 47, 415 {1975).T. A. Alvesalo, T. Haavasoja, and M. T. Manninen,to be published.P. R. Roach, M. W. Meisel, and Y. Eckstein (to bepublished).R. J. Soulen, Jr., and H. Marshak, Cryogenics 22,408 {1980).8A. I. Ahonen, M. Krusius, and M. A. Paalanen, J.Low Temp. Phys. 25, 421 (1976).R. J. Soulen, Jr., and R. B. Dove, National Bureauof Standa ds Special Publication No. 260-62 (U.S. GPO,Washington, D. C., 1979).592

Comparison of the National Bureau of Standards and the Helsinki Temperature Scales and its Effect on the Heat Capacity of Liquid 3He below 10 mK

E. Lhota

M. T. Manninen

J. P. Pekola

A. T. Soinne

R. J. Soulen

Crossref

Comparison of the National Bureau of Standards and the Helsinki Temperature Scales and its Effect on the Heat Capacity of Liquid<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:mrow><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow></mml:math>below 10 mK

Aaltodoc

This is an electronic reprint of the original article.
This reprint may differ from the original in pagination and typographic detail.
Author(s): Lhota, E. & Manninen, M. T. & Pekola, Jukka & Soinne, A. T. &
Soulen, R. J.
Title: Comparison of the National Bureau of Standards and the Helsinki
Temperature Scales and its Effect on the Heat Capacity of Liquid 3He
below 10 mK
Year: 1981
Version: Final published version
Please cite the original version:
Lhota, E. & Manninen, M. T. & Pekola, Jukka & Soinne, A. T. & Soulen, R. J. 1981.
Comparison of the National Bureau of Standards and the Helsinki Temperature Scales
and its Effect on the Heat Capacity of Liquid 3He below 10 mK. Physical Review Letters.
Volume 47, Issue 8. P. 590-592. ISSN 0031-9007 (printed). DOI:
10.1103/physrevlett.47.590.
Rights: © 1981 American Physical Society (APS). http://www.aps.org/
All material supplied via Aaltodoc is protected by copyright and other intellectual property rights, and
duplication or sale of all or part of any of the repository collections is not permitted, except that material may
be duplicated by you for your research use or educational purposes in electronic or print form. You must
obtain permission for any other use. Electronic or print copies may not be offered, whether for sale or
otherwise to anyone who is not an authorised user.
Powered by TCPDF (www.tcpdf.org)
VOLUME 47, +UMBER 8 PHYSICAL REVIEW LETTERS 24 AU| US'I 1981
Comparison of the National Bureau of Standards and the Helsinki Temperature
Scales and its Effect on the Heat Capacity of Liquid 3He below 10 mK
E. I hota, '& M. T. Manninen, J. P. Pekola, and A. T. Soinne
Low TemPerature Laboratory, Helsinki University of Technology, SF-02150 EsPoo 15, Einland
and
H. J. Soulen, Jr.
National Bureau of standards, washington, D. C. 20234
Q,eceived 1 April 1981)
The Helsinki temperature scale, used earlier in measurements of the heat capacity
of liquid He (1-10 mK), is compared with the National Bureau of Standards (NBS) noise
and nuclear-orientation temperature scale. The super fluid transition temperature (T, )
of 3He at zero pressure and the superconductive transition temperatures of tungsten
and beryllium were used as fixed points. T, on the NBS scale was found to be 1.025
+ 0.02 mK, in close agreement with the Helsinki value 1.04 mK. The results support
the Helsinki data on the heat capacity of 3He.
PACS numbers: 67.50.Dg, 07.20.Dt
An internationally accepted temperature scale
in the low-millikelvin region has recently become
important in connection with experiments on nor-
mal and superfluid 'He. The effective mass pg*
of 'He, inferred from the heat capacity data by
Alvesalo stan ,' dev. iates about 30/0 from earlier
results' 4; the major cause of the discrepancy
could be due to different temperature scales. Be-
cause the important Fermi-liquid parameters are
dependent on I*, it is essential to know the cor-
rect specific heat.
The temperature scales used in the various
heat capacity measurements cannot be compared
directly. In the Helsinki experiment"' the tem-
perature scale is fixed to the phase separation
line between the normal and superfluid phases of
'He, but measurements of Refs. 2 and 3 did not
reach this line. An attempt to resolve the dis-
crepancy has been made by Roach, Meisel, and
Eckstein, ' who have measured the volume deriva-
tive of the heat capacity. Their conclusions are
weak, however, because the experiment is also
sensitive to the temperature scale used and it
does not give the heat capacities themselves.
We report in this Letter measurements which
check directly the Helsinki temperature scale em-
ployed in Ref. 1. The test was performed by com-
paring this scale with the National Bureau of Stan-
dards (NBS) cryogenic temperature scale, ' be-
lieved to be accurate to + 0.5% and thus one of the
most reliable scales in the low-millikelvin re-
gion. The superconductive transitions of tung-
sten and beryllium and the superfluid transition
of 'He at zero pressure were used as fixed points
in the experiment. The heat capacity data of Al-
vesalo et al."are strongly supported by our re-
sults.
The Helsinki scale is based on the assumption
that the nuclear spin susceptibility of platinum is
inversely proportional to T. The Curie constant
was found by measuring the spin-lattice relaxa-
tion time ~, and by employing the Korringa rela-
tion, 7,T =%=29.9 ms K. This value for the Kor-
ringa constant K was measured by Ahonen, Krus-
ius, and Paalanen' using a nuclear-orientation
thermometer. The same platinum powder was
employed in Refs. 1 and 8, as well as in the meas-
urements reported here. The Helsinki scale is
given as a set of (P, T) coordinates along the
phase separation curve between normal and su-
perfluid 'He. ' The absolute accuracy of the scale,
+ 5/o, was estimated on the basis of knowledge on
K and the precision of ~, measurements.
The NBS-CTS-1 scale' was established by di-
rectly intercomparing a Josephson junction noise
thermometer and a nuclear-orientation thermom-
eter between 10 and 50 mK and by employing
noise thermometry from 50 to 500 mK. From
the excellent agreement between the two thermom-
eters the absolute accuracy of the NBS scale was
estimated as +0.5% below 50 mK. The scale can
be realized at other laboratories by means of cal-
ibrated super conductive fixed points. '
In our experiments we used the superfluid tran-
sition temperature T, of 'He at zero pressure
(1.04 mK on the Helsinki scale) and the Curie
susceptibility of platinum to produce the Helsinki
scale. The superconductive transition tempera-
tures of one pair of tungsten and beryllium sam-
ples (15.60 and 23.59 mK on the NBS scale, re-
590 1981 The American Physical Society
VOLUME 47, NUMBER 8 PHYSICAL REVIEW LETTERS 24 AUGUST 1981
spectively), immersed in He liquid, as well as
the transition temperatures of two other samples
of the same metals (15.50 and 23.02 mK on the
NBS scale), mounted on the outside of the cell,
were measured on the Helsinki scale.
The experimental chamber, shown in Fig. 1,
was thermally connected to the copper bundle of
a nuclear refrigerator. The platinum NMR coil,
located in a cylindrical appendage to the main
chamber, was a compensated solenoid; the rf-
field inhomogeneity at the platinum sample was
less than 5%%u&. The susceptibility of CLMN (ceri-
um magnesium nitrate diluted to B%%u~ molar solu-
tion by the corresponding lanthanum salt) was
used as a secondary thermometer. The coil as-
semblies for the CLMN pill and the metal sam-
ples were identical; the secondary coils were
connected in series and coupled to a SQUID. Two
separate inductance bridges, with different oper-
ating frequencies, were employed for monitoring
the susceptibilities of CLMN and the supercon-
ducting samples.
The tungsten and beryllium samples outside the
cell (not shown in Fig. 1) were bound with varnish
and cotton thread to a bundle of copper wires,
welded to a cylindrical copper block. A coil form,
with primary and secondary coils, was pushed
around the samples and the spare copper wire
then folded back over the coils. This unit was
connected through a copper rod to the silver sup-
port of the 'He cell. The superconductive transi-
tions of the outside samples were observed with
a simple mutual inductance bridge. '
Because the superconductive transition temper-
ature is very sensitive to magnetic fields, Earth' s
field was compensated with a solenoid outside
the helium Dewar. Furthermore, the tungsten
and beryllium specimens were protected with Mu-
metal and superconducting niobium shields. This
was accomplished by enclosing the samples in-
side the cell within three shields. The inner and
outer ones were Mumetal and the middle one nio-
bium. The samples outside the cell were shield-
ed by a Mumetal can and a niobium cylinder.
The residual magnetic field at the superconduct-
ing samples inside the cell was determined by
measuring the transition temperature as a func-
tion of external static field produced by the pri-
mary coil and by extrapolating linearly to zero
field. The flux change caused by the Meissner
effect was used as a measure of the magnetic
field. The correction to be applied to the transi-
tion temperature turned out to be less than 1%.
The residual field inside the shields of the out-
side samples was estimated to be small.
The calibration between the platinum and the
Ag SIDER
~ ~ ~ % ~ ~ ~ ~ ~
I ~ ~ ~ ~ ~
I IQ
~ ~
1~ ~0
I ~
I
J
I
0
~ I
— Pt SAHPLE
~ NHR COIL
p- ME TAL AND
Nb SHIELDS
PRIMARY AN
SECONDARY
W AND Be
SAHPLES
~ ~
0
~ ~ ~
~ ~
4
~ ~
Ag CHAMBER
Nb SHIELD
P RIMAR Y AND
SECONDARY COILS
CLHN
~ /a
.(I:J~:i:::':).r.8
gl jg/f[
~ I
J
FIG. 1. Experimental cell.
591
VOLUME 47, NUMBER 8 PHYSICAL REVIEW LETTERS 24 AUGUST 1981
TABLE I. Measured values of the superconductive transition temperatures on the NBS scale
and on the Helsinki scale. The absolute accuracy of the NBS values is + 0.1 mK and the preci-
sion of the data measured on the Helsinki scale is + 1 jp.
NBS
scale
(mK)
Helsinki scale (mK)
B = 28 mT B = 28 mT JS = 0 B = 28 mT 8 = 28 mT
T, of 3He,
NBS scale
(mK)
W inside 15.60
W outside 15.50
Be inside 23.59
Be outside 23.02
16.31
15.65
23.73
23.00
16.29
15.90
23.66
22.96
16.29
15.86
23.54
22.97
16.29
23.68
16.30
23.60
1.00
1.02
1.04
1.04
CLMN thermometers was made from 1 to 24 mK.
The superfluid transition point of 'He was found
by means of the CLMN thermometer, with a pre-
cision of 0.1%, as a change in the slope of the
temperature drift curve; this point was employed
to fi.x the Curie constant of platinum. The tung-
sten and beryllium transition temperatures were
recorded with both thermometers.
In Table I we show the measured superconduc-
tive transition temperatures from five different
runs on the Helsinki scale. The external magnet-
ic field (outside the shields) was either zero or
28 mT, the field employed for platinum NMR.
The superfluid transition temperatures on the
NBS scale were obtained by assuming that both
scales are proportional to the absolute tempera-
ture and by multiplying the Helsinki T, = 1.04 mK
by the ratio of the NBS and averaged Helsinki
transition temperatures for each superconductive
sample.
In our measurements the tungsten transition is
more precise because it is sharp and at a lower
temperature. The scatter in the data of the sam-
ple outside the cell is possibly due to lack of
thermal equilibrium between the sample and the
thermometers. The beryllium transition oc-
curred in a temperature interval of about 0.5 mK,
but the width of the main part of the transition
was less than 0.1 mK.
The values derived from the beryllium data
agree with the Helsinki results T, = 1.04 mK,
whereas the data from tungsten inside and out-
side the cell differ from this result by 4.5% and
2%, respectively. Because the source of this dis-
crepancy is not clear, we chose to take an aver-
age of the last column in Table I, giving equal
weight to all of the samples. In this manner we
find T, = 1.025+ 0.02 mK for the superfluid transi-
tion temperature of 'He at zero pressure on the
NBS scale. The difference from the Helsinki val-
ue is 1.4%, i.e. , of the same order as the error
limits of this experiment.
In summary we find that the Helsinki scale,
with T, = 1.04 mK, agrees well with the NBS
scale. This implies that the Korringa constant
for our platinum sample, K = 29.9 ms K, on which
the Helsinki scale is based, is quite correct.
The consistency of the two scales demonstrates
that an accurate temperature scale in the milli-
kelvin region can be established by using the nu-
clear Curie susceptibility of platinum, with the
superfluid transition temperature of 'He employed
as a fixed point. Our results also clearly show
that the heat capacity data of Alvesalo et al. ' do
not suffer from significant errors traceable to
the Helsinki temperature scale.
We are grateful to O. V. Lounasmaa for helpful
comments and discussion. This work was finan-
cially supported by the Academy of Finland.
(a)Permanent address: Research Institute of Elec-
trical Engineering, 25097 Praha 9, Bechovice, Czech-
oslovakia.
'T. A. Alvesalo, T. Haavasoja, M. T. M~~ninen, and
A. T. Soinne, Phys. Rev. Lett. 44, 1076 (1980).
2W. R. Abel, A. C. Anderson, W. C. Black, and J. C.
Wheatley, Phys. Rev. 147, 111 (1966).
A. C. Mota, R. P. Platzeck, R. Rapp, and J. C.
Wheatley, Phys. Rev. 177, 266 (1969).
J. C. Wheatley, Rev. Mod. Phys. 47, 415 {1975).
T. A. Alvesalo, T. Haavasoja, and M. T. Manninen,
to be published.
P. R. Roach, M. W. Meisel, and Y. Eckstein (to be
published).
R. J. Soulen, Jr., and H. Marshak, Cryogenics 22,
408 {1980).
8A. I. Ahonen, M. Krusius, and M. A. Paalanen, J.
Low Temp. Phys. 25, 421 (1976).
R. J. Soulen, Jr., and R. B. Dove, National Bureau
of Standa ds Special Publication No. 260-62 (U.S. GPO,
Washington, D. C., 1979).
592


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Comparison of the National Bureau of Standards and the Helsinki Temperature Scales and its Effect on the Heat Capacity of Liquid 3He below 10 mK

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