The SI unit of radiation dose is "gray" (Gy) which is radiation equivalent to 1 J/kg. A small energy delivered as ionizing radiation can create huge damage at the cellular level, and the sievert is a unit of the health effect of radiation proportional to the radiation dose, but multiplied by factors allowing for the absorption and and the nature of the radiation. Which of these statements are true? You may need to research these answers, but they are useful to know. A dose of 4 to 5 sieverts will kill a human with a 50% probability within 30 days if the dose is received over a short period (say accidental exposure). The background 50 km from the site after a nuclear weapons detonation is 1 sievert. The background radiation flying in a commercial aircraft is 10x the natural background at the surface of Earth. O The dosage from a dental X-ray is 1 milli-sievert. The natural background radiation is about 1 milli-sievert a year O NASA astronauts are allowed to receive a dose of 1 sievert during their careerCarbon -14 is an unstable isotope of carbon (6 protons and 8 neutrons in its nucleus) that is found in Earth's atmosphere in small concentrations. It is made when neutrons produced by cosmic rays collide with common nitrogen-14 nuclei (7 protons and 7 neutrons in its nucleus), freeing a proton and adding a neutron. The natural most abundant isotope is carbon-12 (6 protons and 6 neutrons) is stable, but Carbon-14 with two extra neutrons is not. It has a half life of 5730 years. If a living thing absorbs carbon from air, and then centuries later is uncovered by an archaeologist, its remains can be dated by the presence of the remaining carbon-14. How much carbon-14 is left after 20,000 years? O a little less than 0.1% about 15% O a little less than 1% O a little less than 10%