Defining the Detection Limits of Radiation Detectors

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Radiation is governed by the inverse square law.

This law generally applies when some force, energy, or other conserved quantity is evenly radiated outward from a point source in three-dimensional space, as depicted in the diagram below.  

If you are not familiar with inverse square law, we recommend clicking here for a good explanation: 

Inverse Square Law
Inverse Square Law


S represents the light source, while r represents the measured points. The lines represent the flux emanating from the sources and fluxes. The total number of flux lines depends on the strength of the light source and is constant with increasing distance, where a greater density of flux lines (lines per unit area) means a stronger energy field. The density of flux lines is inversely proportional to the square of the distance from the source because the surface area of a sphere increases with the square of the radius. Thus, the field intensity is inversely proportional to the square of the distance from the source. 

Radiation Detector Technology

The detection limit of a radiation detector also varies according to the technology utilised. 

A scintillation probe will be able to measure lower doses with greater accuracy and precision than a Geiger Müller tube device. 

Thermo Scientific RadEye PRD
Hand Held Scintilation Detector

In terms of accuracy, the measured reading does not change with distance and the strength of the measured radiation. Once the distance is too great and you fall below the minimum threshold of the background radiation you will only observe the background radiation level. Typically, around 0.10 uSV/Hr. 

By calculation, as displayed in the above link, if you know the intensity of radiation at a given distance to the source, and you know the minimum measurement dose possible with your radiation survey meter, you will be able to calculate the maximum distance from the source that a measurement can still be made. 

The Latest Geiger Counters
Radiation Detectors with Geiger Müller Tubes


ADM Nuclear Technologies offers a wide range of radiation monitoring solutions that utilise different technologies and formats.  

It is very much the application that determines the type of radiation monitoring equipment that should be used. Do not hestitate to contact ADM Nuclear Technologies. Our expert team is on hand to give advice and assist in selecting the most appropriate radiation monitoring solution. Please 


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7 March 2023