The counter Geiger (or Geiger-Muller) is one of the best-known tools for identify the presence of ionizing radiation. This device, through the ionization of an inert gas, is able to produce and measure a electrical signal, quantified by a number on the display. This is a tool that has also entered the culture pop due to its typical “click” sound, often used in films and TV series. But how it works from a technical point of view? Before delving into this aspect, it is good to say a few words to understand what is radiation And what changes between ionizing and non-ionizing.
The difference between ionizing and non-ionizing radiation
In physics the radiation they are emissions of energy through waves or particles. They are usually classified into two large families: non-ionizing radiation and ionizing. The first are radiations like the microwave, which are not energetic enough to remove electrons from atoms but only manage to do so vibrate.
On the other hand, however, there are ionizing radiations that can “stripping” electrons from atoms through a process known, precisely, as ionization. The result is the formation of a ion pairmade up of a positively charged atom and a negatively charged electron.
How the Geiger counter works
The Geiger counter It is mainly made up of two parts: a sealed tube (also called chamber) filled with inert gassuch as helium, neon or argon, and a display. If the area around the Geiger counter is radioactive, the gas inside the tube ionizes and, therefore, a pair of ions. The device then provides “counts per minute”, that is, a number of ion pairs created every 60 secondsproducing that characteristic click every time a pair is created.
Attention: as soon as you turn on the instrument you may hear a ticking even in “normal” conditions, because in nature there is a natural background radiation which – it is worth clarifying – It doesn’t create any problems for us human beings. As a reference background value we can consider approximately 60 counts per minute.
At the same time the Geiger counter it is a tool that has various limitations: first of all it does not indicate what type of radiation generated the ionsmuch less his energy.
To get these parameters you need to use specific tools which must be calibrated for a specific type of radiation: these are therefore more precise and accurate devices but, at the same time, more complex And expensive.
The invention of the Geiger counter
In closing, it is worth telling the story of this instrument, designed in 1908 by physicists Hans Wilhelm Gieger and Ernest Rutherford. In this first version it was only able to detect alpha particles, and it will be necessary to wait until 1928 to see the meter we know today, the result of the collaboration between Geiger and a PhD student in physics, Walter Muller. It was the latter who understood how increase the sensitivity of the instrumentallowing it to detect all types of ionizing radiation.
