 The advantages of the emitted X-rays are that they are monochromatic and are continuously produced over a years-long period.No electrical power is needed for this emission, which is ideal for portable X-ray instruments, such as X-ray fluorescence instruments.The ExoMars mission of ESA is planned to use, in 2018, such an iron-55 source for its combined X-ray diffraction/X-ray fluorescence spectrometer.