MIMOS II (MIniaturized MOSsbauer Spectrometer ) is a backscattering Mössbauer Spectrometer, developed for space exploration. This application demands the main features of the instrument:

low weight

low power comsumption

mechanical durability

stability over a wide temperature range

automatic measuring procedure

redundant electronic systems because of damages due to cosmic radiation

The spectrometer was constructed for backscattering geometry. This avoids a difficult sample preparation and allows the non-destructive examination of massive samples like rocks or metal surfaces. The picture shows the size of the whole instrument. The original size is 50x50x90 mm³.
The outline of the spectrometer is shown in the following picture. At the front of the instrument one can see the aperture of the collimator behind which the Mössbauer source and the Mössbauer drive are mounted. The detectors are placed around the drive-source-collimator axis. One can see the diode chips at the front and the amplifier electronics in the boxes stretching out behind them. The feed-back amplifier for the drive and the controlling electronics are mounted in the rear part of the spectrometer.

Technical data of the spectrometer:

weight : 400 g

power consumption : 1 W

geometrical size : 50x50x90 mm³.

Based on standard drive systems, which were build in our institute for twenty years, the size and power consumption of the drive was drastically reduced. On principle the drive is a double loudspeaker. By a pick-up coil the actual velocity can be measured and can be compared with the reference velocity via a feedback loop.



Technical data :

mass 56 g

volume 15,5 cm3

resonance frequency 25 - 30 Hz

maximal velocity 15 mm/s

accuracy less than 0.5 %

power comsumption < 30 mW ( inclusive feedback system )

The instrument's geometry as well as the material used for its devices must be chosen carefully to achieve an optimal measurement of the activity of the source. The counting rate is increased by a compact set-up of source, sample and detector with a wide solid angle. The effect, that the shielding from the direct impact of the source on the detector has, is of great importance. Since weight and size should be reduced to a minimum, a Monte-Carlo program (MCMP) was used to calculate the transmission of different shielding set-ups and geometrys of the instrument. The following set-up turned out to be the optimum. The source is situated at the lower end of the shield. The detectors are mounted laterally at the shield. Plates of tantalum are attached at the top to save the electronics from being damaged by radiation. Furthermore background impulses, that reach the detector from behind, are decreased by the plates.


The effect on the measurement of metallic iron with natural enrichment amounts to 10-20 % The spectrum without a sample, measured at a room temperature with 3 keV FWHM, shows the different parts of the background impulses.