Wednesday, June 08, 2011

Geiger Counter

I recently built a geiger counter kit (Chaney Electronics C6981). It can measure the number of times particles of ionizing radiation pass through the tube per minute. So does it work?

First, let's try it on wood:

Now, let's try it on granite:

So indeed, the granite is more than twice as radioactive as the wood!


Andy said...

Is the output from this kit convertable into Sieverts?

t11s said...

There is a big different between a count on a GM tube (which could be caused by beta, gamma ray, or neutrons) and equivalent radiation dose (Sieverts).

First, not every particle is detected by the tube, thus is has an unknown <100% efficiency. The efficiency of counting could be different for different particles.

Second, the different radiation particles have different energies and thus contributions to the number of Sieverts.

It is not impossible to conceive of calibrating with a known radioactive source, but there would be a lot of math involved.

I've heard that a "rough conversion" is 100 counts/minute = 1 microsievert, but that number could be off by quite a lot depending on the tube & circuitry efficiency.

Given the typical background count I am getting around 100 CPM with this kit, and 250 CPM on granite, I'll start to worry when it gets above 1000 CPM.