How to use a Geiger counter

12.08.2016
Blog

Before we rush into the discussion about how to make full use of a Geiger counter, let’s see what is a Geiger counter anyway and why is it needed.

What is a Geiger counter

 

The original detection principle was discovered in 1908, but it was not until the development of Geiger counter in 1928 by Hans Geiger and Walther Muller (about 100 years ago!) that the Geiger-Müller counter became a practical instrument. Since then it has been very popular due to its robust sensing element and relatively low cost to determine whether an object was radioactive and emitting radiation. It is also potentially capable to detect the amount of particle emission by the radioactive substance.

It consists of a Geiger-Muller tube which is filled with an inert gas such as Helium, Neon or Argon at low pressure. A high voltage is applied at one end and the other end is grounded. Though, in different models virtual grounding can be done by attaching the other end by the opposite terminal of power supply.

The gas itself is non-conducting until an ionizing radiation “charges up” the atoms of gas. When the radiation hits atoms of gas, it creates ions (or charged particles) which then enable a flow of electricity across the tube. The electrical pulse thus generated, is used to measure the amount of radioactivity in the object.

 

Why do you need a Geiger counter?

 

A lot of places are infected with radionuclides due to human intervention. You might underestimate the extent of the contamination but ionizing radiations are commonly found in house paints, granite flooring, rock collections and even your household items such as spoons and dinner plates!

The reason is that uranium is often used to paint dinner plates. Although governments in most countries have banned the use of uranium oxide for glazing the plates but there is innumerable number of plates flooding the market with measurable traces of radioactivity. There is a lot of various equipment for measuring radiation and ensuring that the levels are indeed safe. The most famous, however, is Geiger counter.

How to use a Geiger counter

 

Now that you have understood the need to detect traces of radiation in your surroundings, let me give you a guide to properly use a Geiger counter.

There are many varieties of Geiger counter in the market but the basic functions of most of these machines remain the same.

Remember:

Radioactive materials are dangerous. You should never own one or mess with them unless you know what you’re doing.

A Geiger counter produces a “tick” or click when significant radiation is observed. You can easily get a 15-25 CPM (counts per minute) in your natural surroundings. When a radioactive particle goes through the Geiger- Muller tube, it completes the circuit and produces the sound. Check the top view of a Geiger counter, the golden mesh is the Geiger- Muller tube.

There are many units which a Geiger counter uses, like CPM, micro Sieverts per hour, micro roentgen per hour etc. A dedicated button is provided to switch between the units or even the rate of radiation (time)

The sensitivity and the least count (reading after the decimal point) depend on various factors, including the size of the tube. A bigger tube will show more readings. For example if your counter shows a reading of 20 CPM, A Geiger counter with double the size of tube will show 40 CPM. This makes a bigger tube more sensitive and displays even low traces of radiation.

What you need to do, is to set your Geiger counter to a timer (5 minutes at least)

Use the buttons to change the time +1/ -1 minutes. Use the center button to start the count

Push the center button and it will start counting. Put the counter where u want to measure the level of radiation, like a rock, some object or just the background radiation (in surroundings) Let it run for the assigned time and it will give the total clicks of radiation over the period of time. Geiger counter may jump up and down when you try to find radioactivity in your surroundings, but the variations are not of much value. The overall amount is what means the most.

Divide the value by the assigned time and you get the average radioactive behavior of the component (though some Geiger counters display the average value themselves)

For my Geiger counter 100CPM= 1 micro Seivert exposure in an hour. The Value of radioactivity in standard unit may vary depending on the size of tube in your counter. Switch the display to directly check the exposure in mSv or other units

It’s normal to find a range of 7-30 CPM in surroundings. In my opinion, anything below 150 CPM is considered safe, but if the value overshoots this limit, the substance or atmosphere is dangerously radioactive.

How to Differentiate between Different types of Ionizing Radiation

 

Though the Geiger counter cannot tell the difference between different types of radiations but with little variations of your own, you can.

Remember to always take proper precautions like a glove.

Beta particles are fast moving electrons which can be blocked by a thin piece of wood or aluminum. Aluminum also blocks the alpha particle.

  • Use the Geiger counter after blocking the specimen with a sheet of aluminum
  • Note the readings.
  • The value you get is for pure gamma rays.

Alpha particles are positively charged helium atoms, which can be stopped by even a simple piece of paper. Follow these steps to check if your specimen emits alpha particles:

  • Use the Geiger counter to detect the level of radiation with a shield (like paper) on the specimen.
  • Note the readings.
  • The readings you get are for beta and gamma rays.
  • Subtract the gamma radiation reading from previous observations and you get the value of Beta radiations.

TERRA with Bluetooth channel

 

Dosimeter TERRA with Bluetooth channel has the unique feature – automatic subtraction of gamma background at the measurement of beta contamination.

To get the value of alpha radiations note the readings without any kind of shield and subtract the gamma readings and beta readings. The number you get is for alpha radiations in your specimen.

While Geiger counter still remains one of the most widely used equipment to measure radiations, there are various other tools like dosimeters and survey meters which along with the portability, measure radiations with extreme precision.

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