As approximately half of these gamma rays are emitted in the first second and the other half, over the following 59 alongside gamma rays being mostly emitted in a straight line, people laying on the ground will more likely have obstacles serving as radiation protection such as building walls, foundations, car engines, etc. between their bodies and the radiation emitted from both the fireball and the accompanying lower levels of radiation that continue to arrive at the ground for about 1 minute, during the mushroom cloud phase, which is termed "cloudshine". It would also give protection from the even smaller fraction of radiation that changes direction and is randomly reflected and scattered by the air/"skyshine". Approximately "One and one half inches"/37 mm of steel will reduce gamma dose by half. Its half-value thickness.