A source of radioactivity
Thorium minerals are an important source of radioactivity and can be found in uranium deposits. They can be present in cube forms and have a dark red, brown, or yellowish color. The beach sands have monazite, which is a thorium mineral and could present black points of any uranium mineral of the primary group.
In the States, there are few uranium deposits of the first group. From Maine to California, coast to coast, and some parts of the west, there are uranium deposits of the secondary group. Some of them have a high grade. The main point of activity for many explores is located in Holbrook, Arizona, and Grant Junetion.
Prospect uranium can be a difficult task, but its discovery is relatively easy employing the Geiger-Muller Counter which give a signal as soon as is near to the uranium deposit or other radioactive material. The heart of this device is glass tube filled with an inert gas like argon. The tube has two electrodes that work with a potential of 800 volts, although could be higher in special models. When a gamma ray penetrates in the tube, is attracted by the positive central electrode and left an ionized stele in the gas that allow a momentary discharge from one electrode to the other one. This discharge is amplified and registered by the earphones. Also, it is possible note the presence of radioactive material by an amperemeter or when a neon lamp is lighted. The current for this type of potential and amplification is supplied by batteries.
The Geiger-Muller Counter is used for locating radium, count cosmic rays, protect people from radioactive materials, and for searching other minerals. The counters are built for specific use and can work in different ranges of sensibility.
Beginner prospectors when are using a counter and hear a crack think that there is uranium deposit. The noise is due to the reception of cosmic rays and the normal radioactivity of the earth. It is possible that a counter registers 5 to 50 cracking sounds per minute, but these can be called echo and not radioactive signals. Before starting the exploration, is good practice count these cracks per 10 minutes and divide them by 10 in order to know the real count of each echo.
For the normal research, is only necessary carry the counter while is being recognized the place or when is necessary pass near to the probable formation, but to slow walk while the operator is waiting for any change in the gamma ray counts. It is possible find variations in the count and the operator soon will recognize them. Thus, it is possible find sporadic counts when is near an electric storm. Also, when oneself is in a cliff the number of echoes can diminish its intensity. The contamination in the clothes by radioactive material makes a noise without any meaning. When a prospector is walking in a place with known radioactivity must walk very slowly in order to detect the changes in the counts. A rock layer of 90 cm can hide a vein if the counts are bad interpreted.
Expert prospectors when detect a radioactive behaviour delimit the area and divide it in squares of six meters each side. In each corner, take a count per minute and mark the value for each square. If there is a deposit, the squared map reveals the length, wide and direction with good exactitude. See Fig. 3
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