%, ange Aa Rage i eeo ee 1 ceed ile dae! Aha MO LESSENTe : with the latter constituting a reservoir holding about 96 percent of the atoms. Nuclear detonations can also produce carbon 14 by interaction of the neutrons, produced at the time of the explosion, with nitrogen of the atmosphere. Approximately 400 megatons of total yield fired in the air (surface bursts “lose” about one-half of the neutrons into the ground) will produce a sufficient amount of carbon 14 to equal the amount normally pres- ent in that part of the earth’s biosphere that determines radiation exposure to man. However, half of this newly-added carbon 14 “disappears” into the deep ocean within about 33 years.'!9 One-half of that remaining in the atmosphere likewise “disappears” in the following 33 years, until only a few percent remains. Radioactive isotopes act chemically similar to their stable counterparts so that not only is stable carbon but also carbon 14 found in all living cells. Thus, although carbon 14 emits a beta particle of very low energy that travels a very short distance it nevertheless irradiates essentially the whole body at a rate of approximately one milliroentgen (0.001 roentgen) per year. This is the natural background rate for carbon 14. The Data Since nuclear weapons testing started 511 million tons total energy yield have been released. Considering the conditions of firing (surface versus air bursts) about the same amountof carbon 14 was produced from all past tests as is normally pres- ent in that part of the earth’s biosphere that determinesradiation exposure to man. Assuming that most of the carbon 14 produced by the detonation will “disappear” into the deep ocean with a half-time of 33 years, the estimated whole body exposure for 70 years is 37 milliroentgens (0.037 roentgen).! After this 70-year period the dose rate from bomb produced carbon 14 will be about one-quarter of that at the start, i.e., about one-quarter of one milliroentgen (0.00025 roentgen) per year. Thereafter, the activity will persist for thousands of years but at ever decreasing levels. Evaluation The radiation exposure from carbon 14 may account for roughly one-third of the total radiation dose from fallout over the next 70 years. Because of its long radiological half-life, it will persist at low levels of activity for thousands of years. However, even before the 70-year period is completed the dose rate from carbon 14 will be so low as to be non-measurable. This does not mean that the radiation is not “there” but it will 2 mm > er == co C53 17