Principle of nuclear level measurement

The nuclear level measurement technique is used to measure the level of fluid or solid in a closed tank using Gamma rays.

The nuclear level measurement technique can be used for both continuous and point level measurement. it is used in very hazardous conditions where other level measurement techniques fail to operate. Gamma rays are high energy waves, energy enough to penetrate through walls of tanks in industries.

Nuclear level measurement is also known as gamma level measurement.

Technique of Nuclear level measurement:

Nuclear level detector needs following components:

  • A gamma-ray source ( radioisotopes)

  • Continous gamma detector

  • Microprocessor

The Gamma-ray source and the continuous detector are normally placed outside the tank, opposite to each other. The gamma-ray source is fixed the top of the tank looking down and the continuous detector is fixed at the opposite side top to bottom.

The gamma-ray produced from the source can cover the full length of the tank. The ray produced from source is passed through the tank and detected at the detector with full energy on zero level condition.

The amount of radiation detected decreases as the level of the fluid inside the tank raises. As the level starts increasing the amount of radiation detected reduces. Energy reaching the detector will decrease in an inversely proportional relationship to the level.

The microprocessor analysis the detected energy and transmits the process variable in a 4-20mA range analogue signal.

Read also: Ultrasonic level measurement, Selection of level measurement equipment

What are the advantages of the Nuclear level measurement technique?

  • They are non-contacting type level equipment. Installed outside the tank.

  • They can detect both liquid and solid level.

  • Can be installed in highly hazardous areas, where other techniques can’t work

  • Can withstand high temperature and pressure.

  • They can measure level in applications involving mist, foams and intense vapours too.


  • High cost of installation.

  • Discarding the source must be done in an appropriate manner. There is the matter of licensing and cost.

To know more about Direct level measurement techniques