The DAMA/NaI experiment investigated the presence of dark matter particles in the galactic halo by exploiting the model-independent annual modulation signature. As a consequence of its orbit, the Earth should be exposed to a higher flux of dark matter particles around June 2, when its orbital speed is added to the one of the solar system with respect to the galaxy and to a smaller one around December 2, when the two velocities are subtracted. The annual modulation signature is distinctive since the effect induced by dark matter particles must simultaneously satisfy many requirements.
The experimental set-up was made by nine 9.70 kg low-radioactivity scintillating thallium-doped sodium iodide (NaI(Tl)) crystals. Each crystal was faced by two low-background photomultipliers through 10 cm light guides. The detectors were installed inside a sealed copper box flushed with highly pure nitrogen in order to insulate the detectors from air that contains trace amounts of radon, a radioactive gas. To reduce the natural environmental background the copper box is enclosed inside a multicomponent multi-ton passive shield made of copper, lead, polyethylene/paraffin, cadmium foil. A plexiglas box encloses the whole shield and is also kept in a highly pure nitrogen atmosphere. A 1 m concrete neutron moderator largely surrounds the set-up.
The DAMA/NaI set-up observed the annual modulation signature over 7 annual cycles (1995-2002). The presence of a model independent positive evidence in the data of DAMA/NaI was first reported by the DAMA collaboration in fall 1997 and published beginning of 1998. The final paper with the full results was published in 2003 after the end of experiment in July 2002. Various corollary investigations have also been and are continuing.
The model-independent evidence is compatible with a wide set of scenarios regarding the nature of the dark matter candidate and related astrophysical, nuclear and particle physics  (for example : neutralinos, inelastic dark matter, Self-interacting dark matter, and heavy 4th generation neutrinos).
A careful quantitative investigation of possible sources of systematic and side reactions has been regularly carried out and published at the time of each data release. No systematic effect or side reaction able to account for the observed modulation amplitude and to simultaneously satisfy all the requirements of the signature has been found.
The experiment has also obtained and published many results on other processes and/or approaches.
DAMA/NaI has been replaced by the new generation experiment, DAMA/LIBRA. These experiments are carried out by Italian and Chinese researchers.
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