MIMOS II uses a Cobalt-57 gamma ray source of about 300 mCi at launch which gave a 6-12 hr time for acquisition of a standard MB spectrum during the primary mission on Mars, depending on total Fe content and which Fe-bearing phases are present.[3]
Cobalt-57 has a half-life of only 271.8 days (hence the extended measuring times now on Mars after over a decade).
The MIMOS II sensorheads used on Mars are approx 9 cm x 5 cm x 4 cm[2] and weigh about 400g[3]
The MIMOS II system also includes a circuit board of about 100g.[3]
References
^Klingelhöfer G.; Bernhardt B.; Foh J.; Bonnes U.; Rodionov D.; De Souza P. A.; Schroder C.; Gellert R.; Kane S.; Gutlich P.; Kankeleit E. (2002). "The miniaturized Mössbauer spectrometer MIMOS II for extraterrestrial and outdoor terrestrial applications: A status report". Hyperfine Interactions. 144 (1): 371–379. Bibcode:2002HyInt.144..371K. doi:10.1023/A:1025444209059. S2CID94640811.