Since irradiation increases with proximity to the source of radiation, and as it is impossible to distance or shield an internal source, radioactive materials inside the body can deliver much higher doses to the host organs than they normally would from outside the body. This is particularly true for alpha and beta emitters that are easily shielded by skin and clothing. Some have hypothesized that alphas high relative biological effectiveness might be attributable to cells tendency to absorb transuranic metals into the cellular nucleus where they would be in very close proximity to the genome, though an elevated effectiveness can also be observed for external alpha radiation in cellular studies. As in the calculations for equivalent dose and effective dose, committed dose must include corrections for the relative biological effectiveness of the radiation type and weightings for tissue sensitivity.