It is said to be the first experiment ever to cool a mass and a volume of this size to a temperature this close to absolute zero. The cooled copper mass, weighing approximately 400 kg, was the coldest cubic metre in the universe for over 15 days.
The experiment was carried out by CUORE, an international collaboration involving some 130 scientists mainly from Italy, USA, China, Spain, and France, at the INFN Gran Sasso National Laboratory in Rome.
CUORE, which is Italian for heart but stands for Cryogenic Underground Observatory for Rare Events, is an experiment being built at the INFN Gran Sasso underground laboratory to study the properties of neutrinos and search for rare processes.
The CUORE cryostat is the only one of its kind in the world, not only in terms of its dimensions, extreme temperatures, and cooling power, but also for the selected materials and for the building techniques that both guarantee very low levels of radioactivity. CUORE is seeking to observe a hypothesised rare process called neutrinoless double-beta decay, the detection of which could offer a possible explanation for the abundance of matter over anti-matter in our Universe.
CUORE is designed to work in ultra-cold conditions at the temperatures of around 10mK. It consists of tellurium dioxide crystals serving as bolometers (radiation detectors which measure energy by recording tiny fluctuations in detector’s temperature).
When complete, CUORE will consist of approximately 1000 instrumented tellurium dioxide crystals. It will be covered by shielding made of ancient Roman lead, a material characterised by a very low level of intrinsic radioactivity. The mass of materials at the frigid temperatures near absolute zero will be almost two tonnes.
An international team of physicists, including students and postdoctoral scholars from Italy and the US, worked tirelessly for over a year to assemble the cryostat, iron out the kinks, and successfully demonstrate its record-breaking performance. In the most recent operational test of the cryostat, the temperature reached 6 milliKelvins, equal to – 273.144C.
This gives CUORE the distinction of being the coldest cubic meter in the known Universe. The successful solution to a technological challenge of cooling the entire experimental mass of almost 2 tonnes to the temperature of a few millinKelvin was made possible through a strong collaboration with industrial partners of high profile such as the Leiden Cryogenics BV (the Netherlands), which designed and built the unique refrigeration system, and the Simic SpA (Italy), which built the cryostat vessels
CUORE is supported by the Istituto Nazionale di Fisica Nucleare (INFN) – Italy’s National Institute of Nuclear Physics; the Department of Energy Office of Science (Office of Nuclear Physics), the National Science Foundation, and Alfred P Sloan Foundation in the United States.