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BOREXINO has set new standards in the field of ultra-low background experiments. Such a success was only possible by a strict quality control program during the construction phase of the experiment. In this paper, we describe how construction materials and auxiliary systems of the BOREXINO detector were screened for their residual radioactivity with unprecedented high sensitivity. The highly sensitive assay techniques developed for this purpose were also used to validate the purity of water and nitrogen used in the experiment. Moreover, we report on the production of ²²²Rn-free nitrogen and synthetic air with very low ²²²Rn concentration as well as on the successful search for commercial nitrogen with a particularly low concentration of argon and krypton.

Bolometers are low temperature particle detectors with high energy resolution and detection efficiency. Some types of bolometric detectors are also able to perform an efficient particle identification. A wide variety of radiopure dielectric and diamagnetic materials makes the bolometric technique favorable for applications in astroparticle physics. In particular, thanks to their superior performance, bolometers play an important role in the worldwide efforts on searches for neutrinoless double-beta decay. Such experiments strongly require an extremely low level of the backgrounds that can easily mimic the process searched for. Here, we overview recent progress in the development of low background techniques for bolometric double-beta decay searches.

The XMASS experiment aims to detect pp and ⁷Be solar neutrinos, and neutrinoless double beta decay using ultra pure liquid xenon. It requires low background and a low threshold which will also enable us to search for dark matter in the galactic halo.

The first stage of XMASS project is concentrated on dark matter searches utilizes 800 kg liquid xenon detector. The detector design and expected sensitivity for dark matter based on Monte Carlo simulations will be presented.

The new Laboratorio Subterráneo de Canfranc (LSC) was inaugurated on March 2006. We report the first measurements of radon concentration, gamma background and muon fluxes performed in the Laboratory.