Unless radon gas is discovered in a home inspection, most people remain blissfully unaware that rocks like granite, metal ores, and some soils contain naturally occurring sources of radiation. In most cases, low levels of radiation are not a health concern. But some scientists and engineers are concerned about even trace levels of radiation, which can wreak havoc on sensitive equipment. The semiconductor industry, for instance, spends billions each year to source and "scrub" ultra-trace levels of radioactive materials from microchips, transistors and sensitive sensors.