Assertion: cesium | /r/ObjectUse | used in ion propulsion systems
Facets:
value: because of its low ionization potential
type: CAUSE
value: for spacecraft
type: PURPOSE
value: experimentally
type: MANNER
Source sentences:
text: Cesium is used in atomic clocks and more recently in ion propulsion systems.
text: It has also been used experimentally in ion propulsion systems for spacecraft, again because of its low ionization potential.