One important reminder I should include is that radioactive materials and radiation can be hazardous to your health and high levels can cause deadly diseases such as cancer. The Geiger counter can tell when you are near radioactive substances but it does not tell you how dangerous the substance is. So even though this is not a toy, it could lead you to dangerous radiation without warning you of the danger. One example is that a radioactive dust particle could be inhaled or eaten and later cause cancer. The reader should take the proper precautions to prevent personal exposure.
I finally assembled the MightyOhm.com Geiger Counter kit that I got a week ago. It cost $100.00 not including shipping, from Adafruit.com, the Raspberry Pi guys. It is a kit with numerous parts and must be assembled with solder and soldering iron. It comes with a Russian made Geiger tube, which is larger and much more sensitive than my previous Geiger counter. It comes without any instructions so I had to download the .PDF file from MightyOhm.com and read it with Acrobat Reader app. For those who do not know how to read the resistor color code, the website has a full color photo of the assembled PC board so the resistors and caps can be seen.
My opinion is that it’s a good quality kit with all the correct parts (no substitutes) and is easy to assemble for the experienced kit builder. The instructions are simple and assume that you know the resistor color code. Other parts are described in more detail. One thing I really like about this kit is that it runs on two AAA cells, which are much cheaper than the other kit, which uses a 9 volt battery.
I was surprised that this kit has an ATTiny microcontroller, because it does not have a display or any way on the board to indicate what’s going on, other than the LED and piezo speaker.
Apparently this chip is for interfacing the board to a PC or other device that can display and save the counts per minute, etc. The standalone board doesn’t need it.
After assembly I inserted the two AAA cells and turned it on and adjusted the high voltage as instructed. The chirps from the speaker were clear and the LED flashed with each chirp. This kit is much more sensitive than the other kit, one reason being the much larger Geiger tube. I put the old Canon camera lens next to the tube and the counts went up to several per second, much higher than the other kit and much too fast to count visually or audibly. The radiation from the thorium glass in the lens drives the Geiger counter crazy!
The instructions also have a section on installing the completed board into a case. I haven’t seen the case.
Update Feb 15 – I got a mantle for a Coleman lantern still in its package and an orange saucer. This saucer was glazed with a glaze that uses uranium to color it orange. When I put the counter next to the saucer or mantle the clicks get so intense that they are nearly continuous. These make a great demonstration of radioactivity.
Update Feb 20 – I experimented with the orange saucer, the Geiger counter and a piece of aluminum foil. I placed the Geiger tube about a centimeter away from the edge of the sauce and I got the rapid clicks. I then placed a single thickness of the foil between the tube and saucer. I could not discern any difference in the count rate, but my ears and eyes have poor accuracy when doing this estimate. The count rate goes down a lot when the tube is moved away a foot (.3 m) from the saucer, illustrating the inverse square rule.
I have been having fun with my ‘Geiger Counter’ too. I am on a skiing holiday to Finland. We flew at 39,000 feet. The difference in flash rate on the ground and at cruising altitude is very striking. Roughly consistent with a x 50 increase which is what would be expected. Cruising we had only 1/5 of the atmosphere above us equivalent to just 2 meters of water rather than the usual 10 meters of water equivalent. Paul