Featured Research

from universities, journals, and other organizations

Big step towards redefining the kelvin: Scientists find new way to determine Boltzmann constant

Date:
September 20, 2011
Source:
Physikalisch-Technische Bundesanstalt (PTB)
Summary:
Scientists in Germany have succeeded in re-determining the Boltzmann constant. Physicists expect that in the next two years they will be able to reduce the uncertainty to such an extent that a redefinition of the kelvin will be possible. The advance represents a major step toward basing the temperature unit on an unchangeable fundamental constant.

Metrologists are measurement artists who are very precise -- in the case of the Boltzmann constant up to the sixth decimal place. Whoever is able to determine it very exactly will cause a small revolution in the field of worldwide temperature measurement: The temperature unit will then no longer be based -- as before -- on a chemico-physical material property, i.e. the triple point of water, but on an unchangeable fundamental constant.

Related Articles


Scientists of the Physikalisch-Technische Bundesanstalt (PTB) have now succeeded in re-determining the Boltzmann constant. Although the uncertainty of the result is not yet sufficient for a redefinition of the kelvin, it furnishes proof that the procedure selected by PTB is basically a suitable one. The physicists expect that in the next two years they will be able to reduce the uncertainty to such an extent that a redefinition of the kelvin will be possible. These results have been recently published in the scientific journal Metrologia.

Today's temperature definition bears some problems as up to now, the properties of a substance -- the triple point of water -- have been used which is the basis for the definition of the temperature unit "kelvin." However, water does not always equal water -- different effects can influence the triple point temperature. A special problem is the dependence on the isotopic composition and on the impurity concentrations. These values can easily vary when substances are contaminated or contain different isotopes -- i.e. identical atoms with different atomic masses. For this reason, scientists want to define the kelvin via an unchangeable fundamental constant and to make it more reliable in this way. This is the basis for even more exact measurements which might in future be required in science and technology.

The Boltzmann constant k is such a fundamental constant. It allows conclusions regarding the thermal energy to be drawn from the mechanical energy of particles. Worldwide, a great number of research groups are working on the task to define the kelvin via a fundamental constant. European research institutions are cooperating in this field in several joint EU projects. Only if several groups obtain the same result with at least two independent methods will a "water-free" definition of the kelvin become possible. In the long term, scientists are trying to define all base units of the International System of Units (SI) with the aid of fundamental constants. In the case of the metre, this has, for example, already been done via the speed of light.

For the determination of the Boltzmann constant, which is required for the redefinition of the kelvin, many research groups are using acoustic gas thermometry which has also furnished the most exact values so far. PTB has followed an alternative, completely independent path to rule out systematic error sources and, thus, to place the redefinition on a solid basis: Here, Dielectric-Constant Gas Thermometry (DCGT) is used. The method is based on the density determination of the measuring gas "helium" by means of a capacitance measurement or, in other words: The researchers measure to what extent the gas changes the capacitance of a capacitor. From measurements performed at the triple point of water with different pressures in the measuring capacitor, the Boltzmann constant can be determined by means of fundamental relations.

This task makes extreme demands on metrology. Its realization was possible only with the aid of experts from industry and several other PTB working groups. Pressure measurement at 7 MPa must, for example, be carried out with piston gauges exact to one millionth, capacitance measurement even exact to one part in a billion. The required temperature stability is provided by a large bath thermostat which was manufactured and optimized in cooperation with the national metrology institute of Italy.

The developed set-up now allows DCGT measurements to be carried out at the triple point of water and furnishes a value for k of 1.38065510-23 J/K. With an uncertainty of 8 ppm it demonstrates that DCGT is suitable for a determination of the Boltzmann constant at the highest level. However, until the uncertainty of 2 ppm aimed at is reached, some difficulties will have to be overcome. The scientists of PTB expect that this will be possible within the next two years and that then, the way for the redefinition of the kelvin will be cleared.


Story Source:

The above story is based on materials provided by Physikalisch-Technische Bundesanstalt (PTB). Note: Materials may be edited for content and length.


Journal Reference:

  1. Bernd Fellmuth, Joachim Fischer, Christof Gaiser, Otto Jusko, Tasanee Priruenrom, Wladimir Sabuga, Thorsten Zandt. Determination of the Boltzmann constant by dielectric-constant gas thermometry. Metrologia, 2011; 48 (5): 382 DOI: 10.1088/0026-1394/48/5/020

Cite This Page:

Physikalisch-Technische Bundesanstalt (PTB). "Big step towards redefining the kelvin: Scientists find new way to determine Boltzmann constant." ScienceDaily. ScienceDaily, 20 September 2011. <www.sciencedaily.com/releases/2011/09/110920075520.htm>.
Physikalisch-Technische Bundesanstalt (PTB). (2011, September 20). Big step towards redefining the kelvin: Scientists find new way to determine Boltzmann constant. ScienceDaily. Retrieved November 26, 2014 from www.sciencedaily.com/releases/2011/09/110920075520.htm
Physikalisch-Technische Bundesanstalt (PTB). "Big step towards redefining the kelvin: Scientists find new way to determine Boltzmann constant." ScienceDaily. www.sciencedaily.com/releases/2011/09/110920075520.htm (accessed November 26, 2014).

Share This


More From ScienceDaily



More Matter & Energy News

Wednesday, November 26, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Who Will Failed Nuclear Talks Hurt Most?

Who Will Failed Nuclear Talks Hurt Most?

Reuters - Business Video Online (Nov. 25, 2014) With no immediate prospect of sanctions relief for Iran, and no solid progress in negotiations with the West over the country's nuclear programme, Ciara Lee asks why talks have still not produced results and what a resolution would mean for both parties. Video provided by Reuters
Powered by NewsLook.com
Flying Enthusiast Converts Real-Life Aircraft Cockpit Into Simulator

Flying Enthusiast Converts Real-Life Aircraft Cockpit Into Simulator

Reuters - Innovations Video Online (Nov. 25, 2014) A virtual flying enthusiast converts parts of a written-off Airbus aircraft into a working flight simulator in his northern Slovenian home. Jim Drury reports. Video provided by Reuters
Powered by NewsLook.com
Car Park Solution for Flexible Green Energy

Car Park Solution for Flexible Green Energy

Reuters - Innovations Video Online (Nov. 24, 2014) A British solar power start-up says that by covering millions of existing car park spaces around the UK with flexible solar panels, the country's power problems could be solved. Suzannah Butcher reports. Video provided by Reuters
Powered by NewsLook.com
Microsoft Adds Robot Guards, Ushers In Sci-Fi Apocalypse

Microsoft Adds Robot Guards, Ushers In Sci-Fi Apocalypse

Newsy (Nov. 23, 2014) Microsoft has robotic security guards working at its Silicon Valley Campus. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins