Complex sentence: Natural thorium decays very slowly compared to many other radioactive materials, and the alpha radiation emitted cannot penetrate human skin meaning owning and handling small amounts of thorium, such as a gas mantle, is considered safe.
Split into simpler sentences: Natural thorium decays very slowly compared to many other radioactive materials, and the alpha radiation emitted cannot penetrate human skin. As a result, owning and handling small amounts of thorium, such as a gas mantle, is considered safe.