Radioactive methods nucleonic level sensing

A y-ray source (e.g. 137Cs, Co, 226Ra) is frequently used for liquid level measurement and for liquid and solid level detection. The absorption of the y radiation varies with the thickness x and nature of the absorbing material between the source and the detector according to the Beer-Lambert law, viz  

Thin rods held at their node points by flexible seals 

Sensor containing piezoelectric crystal acting alternately as ultrasonic transmitter and receiver 

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