radioactivity has

A fallout shelter is designed to allow its occupants to minimize exposure to harmful fallout until radioactivity has decayed to a safer level.

Thorium oxide gives glass a high refractive index and low dispersion and was formerly used in producing high-quality lenses, but due to its radioactivity has been replaced by lanthanum oxide in modern eye glasses.

The toll on the worst-affected populations and the growth since then in understanding about the critical threat to human health posed by radioactivity has also been a prohibitive complication associated with nuclear power.

Intense radioactivity has also hindered chemical studies of radon and only a few compounds are known.

Many isotopes that are classed as stable ( i. e. no radioactivity has been observed for them ) are predicted to have extremely long half-lives ( sometimes as high as 10 < sup > 18 </ sup > years or more ).