BOLOMETERS AS SPECTROMETERS FOR X-RAY ASTRONOMY.

We have investigated the possibility to use composite diamond-germanium bolometers, originally developed for I. R. astronomy, for the individual detection of X-ray photons. The advantage of a composite bolometer is that it separates the absorption and detection functions. Diamond, as absorber, is especially interesting because of its high-thermal diffusivity and low heat capacity. The thermalization time of the whole device for a 1 multiplied by 1 mm**2 absorber is less than 50 mu s and allows the detection of a few tens or hundreds counts per second without degradation of the spectral resolution. The theoretical energy resolution DELTA E//f//w//h//m is proportional to T C1/2 where C, the specific heat of the bolometer, is a rapidly decreasing function of the temperature T. The expected value of DELTA E is less than 10eV at 0. 1 degree K. Associated with a 10**3 cm**2 telescope such a device, whose performance is essentially signal limited, is able to detect an emission line of 10** minus **7 ph. cm** minus **2 s** minus **1 in 10**5 seconds in the spectrum of a faint X-ray source.