Massive composite bolometers for dark matter detection.

Massive composite bolometers cooled below 0.1K can detect recoil energy of particles with a very high efficiency. By using different absorber materials (Al₂O₃, Ge, Si, LiF, Cr₂O₃, TiO₂...) some identification of dark matter particles will be possible. Resolutions in the 10 eV range for 1 kg of absorber material are theoretically possible at 0.01K if the thermistor is well matched to the substrate. The authors have successfully developed and tested a 25 g sapphire bolometer at 0.1K and have obtained for a 60 keV gamm-line a resolution of 16 keV FWHM, limited by extraneous noise. First bolometric spectra of radioactivity and cosmic ray backgrounds obtained at sea level are presented.