Total posts : 45366
I knew I could count on Carl for creative guesses. One of my other interests is radiation measurement techniques and this device is a Geiger Counter aka Radiation Survey Meter. The high voltage is necessary to operate the Geiger-Mueller tube which is the black cylindrical object in the foreground. The tube is sensitive to beta and gamma radiation and registers 12 counts per minute of background radiation. I have had the tube in stock for many years and just now got around to using it. It is a 1954 vintage surplus tube which was used in Civil Defense survey meters.
The red object Carl asked about is a 100 ohm potentiometer used to adjust the high voltage. Other items look mysterious because of the perspective of the photo such as the piezoelectric speaker (the black disc under the tube on the left) and one of the panel switches (the red and silver cube next to the speaker).
The unit is OK for general surveying but it lacks sensitivity for snooping for common radioactive sources around the house such as some antique glassware and pottery. It registers 650 CPM for a thoriated lantern mantel. In contrast, a scintillation detector I built registers 800 CPM background, 6,000 CPM for the mantel This is interesting because the mantel thorium is an alpha emitter and the scintillator is only sensitive to gamma radiation. The gamma is emitted by daughter products of radioactive decay in this source. I am in the process of making the scintillation detector portable and look forward to some interesting radiation snooping in the outdoor environment. The scintillation probe is immensely more sensitive than a Geiger counter and can be use to identify sources using a multichannel analyzer which is on my to build list.
I have had a sample of “Trinitite” which I obtained when I was a kid. Trinitite is the fused sand from the Trinity site which was produced by the first atomic bomb test in New Mexico. The Geiger counter detects the residual radioactivity of the atom bomb remaining in this sand and it is a bit unnerving to listen to the distant echo of the first atom bomb from over 66 years ago.
These instruments can be purchased but it is much more educational and interesting to design and build my own. Those who dabble with part15 homebrew stuff know what I mean by this.