These by-products, which account for more than 85 percent of the initial radioactivity in the ore, all end up in the waste piles along with almost all of the heavy metals. Radiation occurs when a radioactive element decays by giving off radioactive particles, thereby reducing its own mass and becoming another element. It is generally considered that the period required to reduce the amount of the original material to a point where its danger could be tolerated by life would be ten times the half-life for that element. It can be seen from the chart that uranium undergoes a very long decay series until it becomes the stable, but toxic, element - lead. The period of time involved, when compared to the lifetime of a generation, is virtually forever.
Radiation can be of several types.
In uranium mine wastes the elements which decay by producing alpha radiation are of particular concern. Alpha radiation has a far greater potential to damage living tissue than other types of radiation. Because the tailings contain elements like Thorium 230 with a half life radioactive danger of 76,000 years, they are hazardous virtually forever. Radon Gas - A Particular Hazard Radon gas, a prime source of alpha radiation, is continuously emitted from tailings piles. When radon gas is produced in an undisturbed ore body, it is relatively harmless since moist of it disintegrates long before it can escape from the rock formation in which it is trapped.