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Radioactive Fluorescent Minerals
Most fluorescent minerals are not radioactive, but some uranium and thorium containing minerals are both slightly radioactive and fluorescent.See 3D Stereo pictures of radioactive minerals
(Click picture to enlarge)
Naturally occurring uranium and thorium are unstable elements and go through several steps of radioactive decay before ultimatly becoming the stable element lead. At each step of decay they eject alpha or beta particles. Gamma radiation usually accompanies each of these particle ejections. A gamma ray is a form of electromagnetic radiation like light or radio waves but with much higher energy.
Here is a thorite specimen about one inch from a Geiger Counter. The specimen is about 1 1/2 " and seems to be solid thorite. Thorite is thorium uranium silicate, (Th, U)SiO4. Its two radioactive elements give off plenty of alpha, beta and gamma radiation on their way down to lead.
This Geiger counter isn't designed to read alpha particles and it was not positioned for reading beta so all radiation described on this page is gamma.
The camera caught the meter at almost 0.3
mR/hr (milli-Roentgen per hour ) of gamma radiation but at this low reading
the needle fluctuates wildly. The procedure for reading levels below 0.1
mR/hr is to count the clicks. About 330 clicks ( or counts) per minute
corresponds to 0.1 mR/hr.
This 10 second sample ( above ) of clicks recorded from the Geiger counter at about one inch from the thorite shows around 25 counts / 10 sec. or 150 counts / minute or 0.05 mR/hr.
Exposure to gamma radiation from a point source follows the inverse square law so that if the distance from the source is doubled then the exposure is divided by four. In 1999, when I did these same tests, the readings were higher than now, 2014, and the readings seemed to follow the inverse square law more closely. The Geiger counter may be getting old.
Andersonite, uraninite with autunite, and a uranium glass stopper were tested for gamma radiation at one inch over one minute. Although the meter seemed to detect radiation with short readings, the one minute readings showed no more counts then the background sample above.
James E. Tozour, email@example.com
Last Updated 10/9/2015