A void fraction measurement system has been developed using a small electron source (Sr90)
associated with a commercial semiconductor detector. This system has been designed for
measurements in two-phase helium flow near satured conditions at atmospheric pressure (4.2 K).
Both elements of the system, the source and the detector, are located in vacuum and have their
temperature controlled around 80 K. Energy attenuation and particle counting are both used
to measure void fraction variation through a stainless steel tube 0.25 mm thick.
Ease of use and sensitivity of this method are demonstrated. We present preliminary tests in
static liquid nitrogen and measurements in helium two-phase flow for an upward forced flow.
Measurements have been performed up to 1 g/s mass flow for the full range of quality factor.
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