Guarapari Beach, Brazil

Radioactive beach sands eroded from surrounding mountains.
800 mSv ·a^-1

The beach sands tend to concentrate heavy elements in much the same way that prospectors "pan" for gold. The natural sloshing and washing of the waves tends to remove all of the silt and clay from the soil. This concentrates the remaining heavy particles in the sandy residue.

Since most naturally occurring radioactive materials have large atomic mass numbers, they form very dense (and therefore heavy) compounds.

Ramsar, Iran

Hot springs
700 mSv ·a^-1

These springs are so named because they are thermally hot, but as irony would have it, they are also radioactively "hot". All natural radioactive sources of radiation arise from the decay of unstable atomic nuclei. One of the products of these radioactive decays is radon gas which is found dissolved in the waters of many hot springs.

Radon gas is slightly denser than air and therefore tends to accumulate in depressions and basements. This gas is a strong emitter of alpha particles. Radon is an inert gas and can be easily inhaled without detecting its presence. It can cause serious damage to the sensitive lung tissues.

Radon is also slightly soluble and becomes dissolved in the blood stream

Kerala Beach, India

Radioactive beach sands eroded from surrounding mountains.
35 mSv ·a^-1

In this instance the combination of naturally occurring radioactive minerals in the surrounding rock and the concentration of these minerals by geological processes has created soils which are enriched with radioactive elements.

City of Pripyat,
(near Chernobyl)
Ukraine
Permanently Evacuated

Nuclear accident fallout
5.0mSv ·a^-1

This is not a result of naturally occurring radiation from the surrounding soil, but is inserted here for purposes of comparison.

In 1986 a nuclear reactor in Chernobyl began an uncontrolled, runaway nuclear reaction. The heat produced a massive steam explosion which released large amounts of radioactive material into the air.

Most of this material precipitated out of the air into the nearby farms, villages, and towns making them uninhabitable.

Luckily much of the high level radiation was produced by radio isotopes with short half-lives, and the radiation levels quickly dropped. Nevertheless, the residual background radiation stabilized at a level which has been considered high for human occupation.

It is interesting to compare the levels of radiation that people will happily encounter when it concerns their recreation, and the levels of radiation they will not tolerate when it does not. A one week vacation at Guarapari Beach, Brazil is equivalent to living three years in the City of Pripyat,near Chernobyl. Six months at Guarapari Beach is equivalent to living eighty years (almost a lifetime) in Pripyat.