The Cadmium Zinc Telluride 0-Neutrino Double-Beta (COBRA) experiment is a large array of

cadmium zinc telluride Cadmium zinc telluride, (CdZnTe) or CZT, is a compound of cadmium, zinc and tellurium or, more strictly speaking, an alloy of cadmium telluride and zinc telluride. A direct bandgap semiconductor, it is used in a variety of applications, including ...

(CdZnTe) semiconductors searching for evidence of

neutrinoless double beta decay The neutrinoless double beta decay (0νββ) is a commonly proposed and experimentally pursued theoretical radioactive decay process that would prove a Majorana nature of the neutrino particle. To this day, it has not been found. The discovery o ...

and to measure its

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...

. COBRA is located underground, within the

Gran Sasso National Laboratory Laboratori Nazionali del Gran Sasso (LNGS) is the largest underground research center in the world. Situated below Gran Sasso mountain in Italy, it is well known for particle physics research by the INFN. In addition to a surface portion of the ...

. The experiment was proposed in 2001, and installation of a large prototype began in 2006.

Set up

COBRA is designed to prove the validity of the CdZnTe detection technique. The initial setup of the experiment, in 2007, was an array of four 1-cm³ CdZnTe

semiconductors A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

. This was then upgraded to 64 detectors in a 4×4×4 array. The CdZnTe crystals act as both the detector and source material, as nine of the isotopes in this material are double beta decay candidates. The location of the experiment allows for shielding from external

gamma rays A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...

; to this end, the detectors are also shielded by 5 cm of radiopure

electrolytic An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...

copper and 20 cm of low-radioactivity lead. 7 cm of boron-loaded

polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...

shields the experiment against

neutrons The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave ...

, and the experiment is constantly flushed with

nitrogen gas Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh ...

to prevent contamination with

radon Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colourless, odourless, tasteless noble gas. It occurs naturally in minute quantities as an intermediate step in the normal radioactive decay chains through ...

Results

As of 2016, COBRA had collected about 250 kg days of calibrated exposure. Efforts were focused on reducing the background readings in order to increase the sensitivity of the experiment.

References

External links

Cobra Experiment home page
{{neutrino detectors Neutrino experiments