Magnetic calorimeters for x-ray and gamma-ray detection

Magnetic calorimeters for particle detection are based on the measurement of the change in magnetization of paramagnetic spins upon the deposition of energy. The use SQUID to measure the flux change of ions in a metallic host has been shown to make a fast detector with high energy resolution. Magnetic ions in a metal constitute a well defined thermodynamic system, the properties of which can be calculated with confidence. Such calculations allows one to optimize the parameters of the system, such a size and concentration, to maximize the sensitivity. Magnetic calorimeters appear particularly suited for use in the detection of hard x-rays since the resolution achievable with such devices decreases with increasing heat capacity as only the one third power. Experimental results on magnetic calorimeters are reviewed.