- 74 et QE ' 4 us or oan x hte nhs me . 3 ee . ae a averaye).* In the nbsence of atmorpheric tests these levels ure expected to continue to decline wenerully except for small transitory rises during the next few spring, seapuns. The gn- “i ba in milk. This is less than the 82 “strontium units” predicted around the Nevada Test Site:is among the lowest in the In general, past predictions of levels of strontium 0 in bones. in the upper ranges te avold undercetimations of radiation ex- two of the predicted amounts considering the fact that such predictions require the: application of many scientific - disciplines—nuclear physics, meteorology, chemistry, -plant and ° animal physiology, etc.-often-to new situations. eene oe percent of the bone dose received during the same 7U-year period from natural background sources. boty‘ particle of very low energy that travels a very alert Although its radio- Sh eg, active half-life is long-6760 years—the process of natural soe ~e cn ee ee rE ilMR et Carbon 14 ie produced naturally by interaction of coamic ae at a rate of approximately one milliroentgen (0.001 roentgen ra per year. This is the natural backgroynd rate fer carbon Pig The Date wa, : ‘Bince nuclear weapons testing started 61) million luna totu energy yield huve been released. Considering the conditions of firing (surface versus six bursts) about the sare vmount of carbon'14 was produced from all past tests as ie herimally prev entin that part of the earth's biosphere that determines radis tion exposure to man. Assuming that.most of (ie carbon1 produced by the detonation will] “disappear” Inte tiv drep ocea: with a half-time of 33 years, the estimated whole buds exposur ; for 70 years is 37 milliroontgens (0.037 roentgen). carbon 34 will be about one-quarter of that at tlic start, bog about one-quarter of ene milliroentgen (0.00025 i ocutven) peg year. Thereafter, the activity will persist for shousands Background Information production had been going on for wuch a great time thet the rate of production and rate of decay were in equilibrium, i.e,, just aa much is formed each year as decays away, until nuclear test detonations were initiated. There is a constant exchange of carbu:. 14 atoms between the almousphere and the surface of the earth on the one hand, and the deep ecean on the other, 56 . 5 - * cent of the atoms. Nuclear detonations can alse produce earbou di ty iter: slg After this 70-year period the dose rate from benih produce3g F. CARBON 14 rays with the nitrogen inthe atmosphere. * - giatance it n-vertheless irradiates essentially the whole body That segmentof the U.S, population whosebones will receive the highest radiation dose are children born in 1963 in regions The predicted average 70-year radiation dose to the bones of the age group receiving the highest exposure from all past tests—about 466 milliroentgens (0.465 roentgen) from ail radioactive materials wilhin and outside the body—is about five vr Radioactive isotopes att chemically-gimilar to their stabi am counterpurts so that not only ia stable garbyn byi visu carbae 14 found in all living cells.” Thus, altheugh varbon 14 emits » of strontium 90 in bones have been within about a factor of Evaivation tet F Eo a8 a a with the latter constituting a reservoir holding whoot tl per “disappears” in the fullowing 33 years, until only « low percen ’ remains. Even so, it is remarkable that the observed amounts of heavier rainfall. The total radiation exposure to ti sse children—from internally deposited as well as external radionuclides has been predicted to be abuut 465 milliroentgens (0.465 roentgen) accumulated over a 70-year period,t. ° s, > ent in that part of the earth’s biosphere thai cerermine: radiation exposure to man. However, half of this newly -ndde: aa carbon J4 “disappears” inte the deep ocean witli about years,"®) One-half of that remaining in the atmosphere hikewis . have been too high. Thir is duein purt to the selection of data posure. . : fr AE ‘ ar ——-— bo - tons of total yield Gred in the air (surface buretone-half of the neutrons mente the ground) well prone a sul: cient anjunt of carbon 14 to equal the amount cericaliy pre: and should foretell less in the bones than predicted.’ Incidentally, the amount of strontium 10 in the milk produced hole - = * action of the neutrone, produced at the time of tos explosion, * with nitrogen of the atmosphere. Approximate! PU Tyee prat nua) (1/83) national average ‘for thuse ureas of the United States showirg the highest vajues was 26 “strontium units” country. = tm kT Te Sacks: Bt ARTS. 4(EST peOS egw ©, years but nt ever decreasing levels. : Evalvetion The radiation exposure from carbon 14 may aecrount ¥ roughly one-third of the total radiation dove fron (nliout ov the next 7) years. Hecause of its long radiolugicn! half-lli eam it will persist at low levels of activity for thousiis of yea: aa However, even before the 70-year period is compivicd the dow rate from carbon 14 will be so low as te be ne: mensurabiggt This does nol mean that the radiation is not '') 9. tut it » ia