[en] The objective of this research project was to design and build a measuring system using a combination of commercially available instruments for density, pressure and temperature measurements. For density measurement the beta radiation absorption method was selected. A special housing was developed and designed to cool and protect the electronic components. The density measuring equipment was calibrated under laboratory conditions and tested under the ambient conditions of containment LOCA experiments. The results show that the beta densitometer can be used in containment experiments to measure the expected density of the steam-water-air mixture which ranges from 1.2 to 8 kg/m³. Using the present measuring equipment, especially the present strontium 90 beta emitter, it is possible to measure the density over a length of 250 mm with a time constant of 3 ms and an uncertainty of less than +-7.5%. If a stronger strontium 90 source is used the measuring length can be enlarged up to a maximum of 500 mm