Particle detection using cryogenic magnetic calorimeters

Magnetic microcalorimeters have been developed to detect X-rays with energies up to 100 keV. The magnetization of localized paramagnetic ions embedded in a metal is measured with a SQUID and is used to determine very small temperature changes resulting from the absorption of energy. The response of such detectors can be calculated from equilibrium statistical thermodynamics. Our present best result of 90 eV resolution at 6 keV has been obtained with a calorimeter of 600 ppm Er3+ in Au at 55 mK, at which temperature the detector had a heat capacity of 3 x 10(-12) J/K. Upon optimization of the parameters of the calorimeter a resolution of less than 2 eV is predicted to be achievable at 50 mK and less than 1 eV at lower temperatures. The coupling of the conduction electrons to the ions leads to very fast thermalization times even at low temperatures. (C) 1999 Elsevier Science B.V. All rights reserved.