Most gamma rays, being more energetic than x-rays, pass through the body to the outside. Because the absorbed beta and gamma radiation is spread over a larger volume, it is less concentrated and less harmful. A single radon atom can cause lung cancer Carcinogens cause random damage to the chromosomes and DNA molecules contained in the nucleus of the cell. Most of these cells are either killed or sterilized. However, in a very few cases, one of these damaged cells may survive the injury and still be capable of reproducing.
Most cancers are of monoclonal origin, that is, they originate from damage to a single cell.
Even a single alpha particle can cause major genomic changes to the cell's DNA, including mutation and transformation. Even allowing for a substantial degree of repair, the passage of a single alpha particle has the potential to trigger cancerous growth of cells, which it does not kill outright. The Los Alamos National Laboratory researchers discovered in 1997 that alpha particles emitted by radon do not have to hit the nucleus of a cell to damage the cell's DNA, which resides in the nucleus. This negates the widely-held assumption that alpha particles cause genetic changes only through direct traversals of cell nuclei. Merely the interaction of alpha particles with the fluids that line the lungs damages the DNA of nearby cells.