Physicists' findings about helium could lead to more accurate temperature measurements

May 17, 2010
Wojciech Cencek, a postdoctoral researcher at the University of Delaware, was involved in research on helium that may lead to more accurate standards for how temperature and pressure are measured. Credit: Ambre Alexander/University of Delaware

In the May 7 edition of Physical Review Letters an international team led by University of Delaware researchers reports new findings about helium that may lead to more accurate standards for how temperature and pressure are measured.

In the article, highlighted as an "Editor's Suggestion" by the journal, the scientists provide a new theoretical computation of the force acting between a pair of helium , referred to as "pair potential," that is more accurate than any published to date.



Helium has a number of characteristics that make it special, Szalewicz says. It is the most stable of all the elements and has the lowest boiling point. It becomes a fluid at temperatures close to while most other materials are a solid. In fact, helium is a liquid even at absolute zero and becomes a solid only at high pressure.


"Of all the elements, helium is closest to the ideal gas," Szalewicz says. "Two helium atoms form the weakest bound . All the properties of temperature, for example, which is a measure of the of particles in matter, can be modeled if the force acting between a pair of helium atoms is known.

"This has been the subject of extensive activity," Szalewicz notes, "as accurate knowledge of the pair potential of helium is of importance in several branches of science, including low-temperature condensed matter physics, spectroscopy, and metrology, which is the science of measurement."


The scientists predict that the binding energy of two molecules of helium, chemically referred to as a "dimer," is 6,790 times smaller than the potential depth, and the average separation between the atoms is 47 angstroms compared to the typical chemical bond length of about 1 angstrom. The estimated uncertainties of the theoretical results are an order of magnitude smaller than the best experimental ones, they report.

The thermophysical properties of gaseous computed from this potential now will be used to calibrate the apparatus for measuring properties such as viscosities or the speed of sound.

"These calculations should lead to new, better standards for quantities such as temperature or pressure," Szalewicz says. "Continuous improvement of metrology standards is important for progress in experimental science, as well as in many industrial applications."

Explore further: Probable observation of a supersolid helium phase

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1 / 5 (1) May 17, 2010
Anybody know what would it be like if humans explored a planet with a helium atmosphere? I know we would die without oxygen, but would it sound very cartoony?
1 / 5 (2) May 17, 2010
Hopefully the return of the fundamental electrodynamic asymmetry (as Maxwell's full unedited original equations abundantly illustrate) of the system will emerge.

Then you will finally understand where the arrow of time comes from.


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