. .

UK leads the way in race for new temperature definition
by Staff Writers
London, UK (SPX) Jul 12, 2013
 illustration only

Scientists at the UK's National Physical Laboratory (NPL) have performed the most accurate measurement yet of the Boltzmann constant. While the impact of such an achievement is not immediately obvious, the measurement could revolutionise the way we define temperature, replacing the standard method that has been used for over 50 years.

The new measurement is 1.380 651 56 (98) + 10-23 J K-1, where the (98) shows the uncertainty in the last two digits, which amounts to an uncertainty of 0.7 parts per million --almost half the previous lowest uncertainty.

The result has been published in the journal Metrologia by IOP Publishing on behalf of the Bureau International des Poids et Mesures (BIPM).

Scientists currently define the kelvin and the degree Celsius using the temperature of the triple point of water - the point at which liquid water, solid ice and water vapour can all exist in equilibrium.

This 'standard temperature' has been defined as 273.16 K exactly. The temperature measurements we make in everyday life are an assessment of how much hotter or colder an object is compared to this value.

As temperature measurements need to be made with increasing accuracy across a wide range of disciplines, fixing a single temperature as a standard becomes problematic, especially when you're measuring extremely hot or cold temperatures.

Lead author of the study, Dr Michael de Podesta, said: The further away one measures from the temperature of the triple point of water, the harder it gets to precisely determine the ratio of exactly how much hotter or colder the temperature is than the standard temperature. This adds uncertainty to temperature measurements on top of the normal practical difficulties."

The solution is to redefine the kelvin using a fixed constant of nature, just as the metre has moved from a physical piece of metal to the length of the path travelled by light in vacuum over a specified number of nanoseconds. The suggested method is to use the Boltzmann constant, which is a measure of the relationship between the kinetic energy of molecules and temperature.

"It is fascinating that we worked out how to measure temperature long before we knew what temperature actually was. Now we understand that the temperature of an object is related to the energy of motion of its constituent atoms and molecules. When you touch an object and it feels 'hot' you are literally sensing the 'buzzing' of the atomic vibrations. The new definition directly links the unit of temperature to this basic physical reality," continued de Podesta.

In this study, the researchers, in collaboration with Cranfield University and the Scottish Universities Environmental Research Centre (SUERC), used acoustic thermometry to make the measurement by building an acoustic resonator and making amazingly precise measurements of the speed of sound in argon gas.

The researchers first cooled the resonator to the temperature of the triple point of water so they knew the temperature exactly in the current definition and filled it with argon gas that had its isotopic purity assessed by the SUERC team.

Then they used the speed of sound measurement to calculate the average speed of the argon molecules and hence the average amount of kinetic energy that they had - from this they were able to calculate the Boltzmann constant with an extremely high accuracy.

In order to achieve this high accuracy, the researchers also needed to measure the radius of the resonator with a high accuracy.

The team at Cranfield University used a single-crystal diamond cutting tool to produce four copper hemispheres. The best pair, when put together, formed a triaxially-ellipsoidal resonator that was the correct shape to within one thousandth of a millimetre. The radius was then calculated using the specific frequencies at which the wavelength of microwaves exactly fit into the resonator and was measured with an overall uncertainty of 11.7 nm, which is the thickness of about 600 atoms.

"This experiment has been exhilarating, and after six years we are exhausted. Every aspect of the experiment has required pushing science and engineering to the limit. In this kind of work we need to worry constantly about all the things which might go wrong, and how they might affect the results. We are looking forward to worrying a little less and getting on with exploiting some of the new technology we have invented in the course of the project," continued de Podesta.

"A low-uncertainty measurement of the Boltzmann constant" (de Podesta M, Underwood R J, Sutton G, Morantz P, Harris P M, Mark D F, Stuart F M, Vargha G and Machin G 2013 Metrologia 50 354-376)

 .

 Tweet

Vienna, Austria (SPX) Jul 12, 2013
Objects that are smaller than the wavelength of thermal radiation cannot radiate heat efficiently. A generalized theory of thermal radiation has now been experimentally confirmed at the level of a single object at the Vienna University of Technology. All the objects around us emit thermal radiation. Usually, this radiation can be described very accurately using Planck's law. If, however, t ... read more

 Scientist says Earth may once have been orbited by two moons Dust hazard for Moon missions: scientists NASA Seeks Information on Commercial Robotic Lunar Lander Capabilities Orbiting astronaut controls robot on Earth, testing feasibility of CU-Boulder project on far side of the moon DNA-sequencing chip could be sent to Mars to search for signs of life Opportunity Making Progress Toward Solander Point Mars Rover Curiosity Begins Trek Toward Mount Sharp Science Team Outlines Goals for NASA's 2020 Mars Rover NASA Selects Seven Projects for 2014 X-Hab Innovation Challenge Space seeds could "benefit" traditional Chinese medicines Kennedy Facilities Key to NASA's Transition Voyager 1 Explores Final Frontier Of Our Solar Bubble China's space tracking ship Yuanwang-5 berths at Jakarta for replenishment China plans to launch Tiangong-2 space lab around 2015 Twilight for Tiangong China calls for international cooperation in manned space program Station Astronauts Complete First of Two July Spacewalks Russia to go ahead with space freighter launch ISS technology to 'hear' potential leaks Russian cosmonauts conduct space station tasks in spacewalk Special group to be set up for inspecting production of Proton-M carrier rockets Two Rockets Launched From Wallops Specialists unrelated to Khrunichev to check Proton-M rocket production Proton Rocket to Stay in Demand Despite Accidents Hubble Finds a Cobalt Blue Planet Gaps in dust around stars may not indicate planets as many believe Hubble Telescope reveals variation between hot extrasolar planet atmospheres UCSB Astronomer Uncovers The Hidden Identity Of An Exoplanet Cool it, quick: Rapid cooling leads to stronger alloys Bioengineers Use Adhesion to Combine Silicones and Organic Materials NASA's OPALS to Beam Data From Space Via Laser Experts row over 'earliest' Chinese inscriptions find

 The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement