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Radioactive Minerals and Rocks

Updated on March 2, 2014

B. Boltwood discovered radium in 1905 came from the decay of uranium and uranium was present in many minerals such as zircon and monazite. Also introduced the concept of radiogenic lead, ie, Pb as the end product of the decay of uranium. Note that in geologically ancient rocks the lead-uranium ratio is higher than in most rocks and invents new dating of rocks and minerals by measuring the ratio of uranium and lead revolutionizing geology. You can estimate the age of the earth from its rocks.

From here, it happened in avalanche discoveries that led to the determination of the natural radioactive series, the discovery of artificial radioactivity or explanation of the nature of cosmic radiation, among others.

Brief History

In 1789 MH Klaproth obtained from pitchblende (a variety of uraninite, UO2) a black powder which he claimed contained a new chemical element. However, it was E. Peligot who in 1841 first isolated uranium metal.

In 1896 H. Becquerel observed that only uranium (VI) were fluorescent and / or phosphorescent and this property was independent of sun exposure. Meanwhile, uranium (IV) were not fluorescent or phosphorescent, however emit invisible radiation that could penetrate aluminum foil and impress a photographic plate. Becquerel suggests the existence of "uranic rays", what is now known as radioactivity.

Marie and Pierre Curie observed that uranic Becquerel rays were not exclusive of uranium and thorium also appeared in addition to the polonium and radium found in 1898 both.

Radioactivity on Earth

Today we know that around 80 % of the background radiation we receive annually for life on Earth ( 2 mSv on average , as a head CT ) made of minerals around us , cosmic radiation and the food we eat . Therefore , it seems whimsical learn more minerals and rocks (which are heterogeneous mixtures of minerals) radiating us daily.

Our planet series came in about 4500 million years ago with a few radioisotopes, which we call primary by having at least as long half-lives such as age of the Earth itself . The most important for its abundance and contribution to the background radiation are the K -40 (found in foods such as clays and rocks ) , Th- 232 and U -238 , U -235 ( present in many minerals). They form large cations that require minerals and rocks with large crystalline structures to house them.

Radioactive decay of radioisotopes and successive primary side series isotopes, as in the case of uranium , radium , sometimes produce more intense than the primary radiation emerging . Having shorter than the age of the earth half-lives , their existence can only be explained by the primary . One of the side radioisotopes most relevant for their contribution to the background dose is radon ( Rn- 222) , being a gas, is the main source of radiation by inhalation. Radon is continuously emanating from the Earth's surface.

Finally , tertiary radioisotopes are those who are continually in nature induced by nuclear reactions caused by cosmic radiation. Among those named have the tertiary C -14, which has become very useful for dating organic remains .

Although radioisotopes are distributed around the Earth's surface in a more or less uniform, there are regions in which different geological and geochemical reasons , concentrations of radioactive elements are abnormally high . Moreover , contrary to what one might think , uranium and thorium are much more abundant in nature than other elements being in a proportion almost 1000 times higher than gold, for example.

Then I will present very shallow way rock types in which tend to concentrate radioactive minerals and some examples of these.

Potassium (K): Silvina (KCl) used in fertilizers and micas (muscovite, biotite, lepidolite, phlogopite), used in industry for thermal and electrical insulation.
Potassium (K): Silvina (KCl) used in fertilizers and micas (muscovite, biotite, lepidolite, phlogopite), used in industry for thermal and electrical insulation. | Source
Muscovite Mica, KAl2 (Si3Al) O10 (OH) 2
Muscovite Mica, KAl2 (Si3Al) O10 (OH) 2
Uranium (U): autunite, carnotite, pitchblende, torbernite, used as uraninite uranium ore for energy and steel industry.
Uranium (U): autunite, carnotite, pitchblende, torbernite, used as uraninite uranium ore for energy and steel industry.

Rocks and Minerals

Igneous rocks (granite, pegmatite , rhyolite , tuff , etc. . ) Formed upon cooling and solidification of magma or molten rock inside the earth often contain radioactive elements distributed within very fine crystalline particles . But the radioactivity is not exclusive to these rocks because sometimes deposits of rocks formed by the accumulation of sediment or sedimentary ( conglomerates , clays , sandstones , shales , limestones , etc. . ) , Being porous and permeable mineral staying well of U and Th leading to significant deposits of radioactive minerals. Metamorphic rocks (marble , quartzite , metamorphic schists , gneiss , slate, etc. . ) Formed at high pressures from igneous or sedimentary rocks tend to keep the content of radioactive minerals of the original rock .

The phosphate deposits ( ores sedimentary rock composed of apatite group ) and carbon ( hydrocarbons ) having a special consideration because both phosphates as well accommodated hydrocarbons cations huge U and Th , so that in some cases the deposits containing high concentrations of uranium .

To summarize , in general, we think that the concentration of radioactive elements in rocks is :

- Frequent in granite, slate, shale , coal, phosphate deposits ,
- Occasional in andesite , conglomerate , sandstone , gneiss,
- Rare in basalt , limestone, gypsum and salt deposits , quartzite, marble.

Given the above, one can understand why Pontevedra ( abounding in granite) are exposed to levels of natural radiation almost four times higher than those of Murcia ( abounding in marble) , according to the results of Marna Project ( Map Natural Gamma radiation ) available on the website of CSN.

As for minerals, in Nature there are hundreds of radioactive isotopes. Some of them are really aesthetic and therefore are exposed in public museums and private collections. Among the most representative containing potassium , uranium and thorium (plus its decay products ) we find the following :

- Potassium ( K): Silvina (KCl ) used in fertilizers and micas (muscovite , biotite, lepidolite , phlogopite ) , used in industry for thermal and electrical insulation .

Precautions with radioactive minerals

n a society where a priori radioactive everything is bad , it is not surprising that the issue of the danger of radioactive minerals is a recurring theme among fans minerals. Therefore, it is worth giving some recommendations for proper handling and storage that, in general , be virtually the same as those to follow any other mineral.

Normal functioning of the kidney , brain , liver and other systems can be affected by uranium exposure since it is a toxic chemical element by itself and we must not forget to manage their compounds. But also, as both their thorium minerals have basically three types of risks due to radioactivity. These risks are external irradiation , ingestion internal irradiation and internal irradiation by inhalation of radon products .

The risk of external radiation is usually not too serious because an important part of the release of uranium and thorium is in the form of alpha particles are stopped mostly by a thin layer of air. In addition , by decreasing the radiation received by the square of the distance , simply by placing copies on the inside of the drawers or cabinets is much reduced dose . Also, obviously avoiding reckless behavior, such as collecting samples of large and very rich , numerous samples stored under the bed , carry them in your pocket or turning the house into a nuclear graveyard.

Internal radiation by ingestion can be avoided by not eating or smoking while handling minerals , washing hands after etc. . In this line , the solubility of the mineral and its degree of division are properties that must be taken into account. Fortunately, many radioactive minerals that tend to appear in powder form, such as carnotite , are also very insoluble .

Finally , irradiation of radon inhalation may be the biggest risk of radioactive minerals. This gas is produced by decay of radium , which in turn is of the uranium and thorium. Radon is a chemically inert gas with a short half life . The risk appears when it disintegrates , resulting in highly reactive chemically relatively long life and isotopes that bind any particle present in the air ( from, for example , of the snuff smoke ) and thus can reach and irradiate the lungs . It is now considered that this radiation is a major risk factor in the development of lung cancer. Precautionary measures to be taken can range from storing radioactive minerals in well ventilated places do it in airtight containers .

Therefore, the rational conservation of radioactive mineral samples is as safe or more than any other mineral conservation shows that , ultimately, it is still a chemical compound whose risks must know and understand activity.

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