Detection of single X-ray quanta with a magnetic calorimeter

We give a status report on the development of a particular low temperature calorimeter with new experimental results. On absorption of an X-ray photon the increase of temperature changes the magnetization of a diluted magnetic sample, and this quantity is measured with a SQUID-magnetometer. It is a special feature of this experimental method that the magnetic sample has a very high heat capacity and an additional absorber for a compound detector does not change the sensitivity essentially. Besides a short summary on earlier measurements we present new results with metallic magnetic samples, which give shorter signal rise times (below 100 μs). On a compound detector with 0.1 g of LaB6:Er and an absorber of 12 g sapphire, the energy resolution for 5.9 keV and 60 keV X-ray sis 1.6 keV and 2.6 keV (FWHM), respectively. With a silicon absorber an energy resolution of 1.4 keV at 5.9 keV has been found. The energy resolution is in any case limited by two effects. On the one hand the signal height is strongly reduced due to an additional heat capacity of the magnetic sample and on the other had we have an additional noise from the conduction electrons of the metallic sample. Possible improvements with respect to both effects are discussed.