Image credit: INFN.
The CUORE collaboration at the INFN Gran Sasso National Laboratory has set a world record by cooling a copper vessel with the volume of a cubic metre to a temperature of 6 mK. It is the first experiment 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 more than 15 days. No experiment on Earth has ever cooled a similar mass or volume to temperatures this low. Similar conditions are also not expected to arise in nature.
CUORE – which stands for Cryogenic Underground Observatory for Rare Events, but is also Italian for heart – is an experiment being built by an international collaboration at Gran Sasso to study the properties of neutrinos and search for rare processes, in particular the hypothesized neutrinoless double-beta decay. The experiment is designed to work in ultra-cold conditions at temperatures of around 10 mK. It consists of tellurium-dioxide crystals serving as bolometers, which measure energy by recording tiny fluctuations in the crystal’s temperature. When complete, CUORE will contain some 1000 instrumented crystals and will be covered by shielding made of ancient Roman lead, which has a particularly low level of intrinsic radioactivity. The mass of material to be held near absolute zero will be almost two tonnes.
The cryostat was implemented and funded by INFN, and the University of Milano Bicocca co-ordinated the research team in charge of the design of the cryogenic system. The successful solution to the technological challenge of cooling the entire experimental mass of almost two tonnes to the temperature of a few millikelvin was made possible through collaboration with high-profile industrial partners such as Leiden Cryogenics BV, who designed and built the unique refrigeration system, and Simic SpA, who built the cryostat vessels.
