Radionuclides bomb-produced

The atmospheric concentration of natural and bomb-produced radionuclides has been measured at ground level for several years at three locations throughout the world. The manner in which the concentration decreased suggested a half-residence time for stratospheric aerosols of 11.8 months at 46°N latitude. The annual spring concentration maximum occurred one to four months earlier at 71°N than at 46°N. Cosmogenic 7Be attained a maximum concentration before the bomb-produced radionuclides at 71° N and later than the bomb-produced isotopes at 46°N. The rate of increase toward the annual peak concentration for most radionuclides could be approximated by an exponential in which the concentration doubled every 60 days likewise, the rate of decrease from the maximum concentration could be approximated by an exponential with a half-time of about 40 days for most radionuclides except 7Be at 46°N, which shows a half-time of about 60 days. 

The ground-level air concentrations of 7Be and 137Cs at 46 °N and 71 °N are shown in Figure 8. The 137Cs concentration variations are typical of relatively long lived nuclear weapons-produced radionuclides and illustrate the variation in the concentrations of these radionuclides with latitude and time. It is evident that the concentrations and seasonal concentration variations were substantially different at the two latitudes. There also were differences in the seasonal variations between 7Be and the bomb-produced radionuclides. Based on the idealized curves drawn... 

The rate at which the concentration approached a maximum each year was about the same for all radionuclides at 46 °N and 71 °N. This rate could be approximated from the idealized curves by an exponential with the concentrations doubling about every 60 days, as is shown in Figure 9 for 7Be. The rate at which the concentrations decreased after the maximum had been reached was also the same for all of the radionuclides at 71°N and for the bomb-produced radionuclides at 46°N. This rate of decrease was approximately exponential with a half-life of about 40 days. The rate of decrease of 7Be at 46°N was appreciably slower with a half-time of about 60 days. 

The variation in 7Be with altitude and time at 46 °N was very similar to the variations in the activities of the bomb-produced radionuclides, except in the case of short lived fission products whose seasonal variations were obscured largely by debris from recent nuclear tests. Figure 3 shows the 137Cs disintegration rate plotted as function of time for several altitudes. As for 7Be, 137Cs reached a maximum at 40,000 feet and below on June 5, 1967 and then decreased. The activities of 137Cs and the other bomb-produced radionuclides increased sharply again from 20,000 to 40,000 feet after October 23. 

Because of the similarity in the seasonal variations of 7Be and the bomb-produced radionuclides it seems likely that the variations can be attributed primarily to the same cause. Probably radionuclides are transported down into the low polar stratosphere in the winter when the polar stratosphere is least stable and, therefore, vertical mixing is most intense (2). The radionuclides then diffuse quasihorizontally through the tropo-pause gap into the troposphere and eventually to ground level This... 

Earth s surface is through bucket collection of precipitation and subsequent analysis of the water for °Pb obtained over a specific period of time. This method has been used during the assay of precipitation for bomb-produced radionuclides such as Sr and Cs, notably by the Environmental Measurements Laboratory of the Department of Energy and its precursor, the Atomic Energy Commission. Detailed summaries, mainly along —80° W longitude in both hemispheres plus some other selected sites in the continental US, are available from the Department of Energy as unpublished reports. 

Numerous radionuclides have been applied to marine sedimentary problems. These are generally grouped into cosmic-ray produced (cos-mogenic) nuclides ( C, °Be, Be, "Al), nuclear bomb-produced (fallout) nuclides ( Cs, plutonium isotopes, 24iAm), and naturally occurring nuclides ultimately derived from the decay of 38u, and 232xh parents. 

The most extreme case of gamma radiation dose would arise from explosion of a nuclear weapon. Nuclear weapons release intense gamma radiation that can produce fatal doses miles from an explosion (see Chapter 5). A less extreme but more likely scenario involves radioactive materials dispersed via conventional explosives (dirty bombs), where only the immediate area is contaminated with gamma-emitting radionuclides. 

Acute exposures are also typically associated only with external exposures. While it is conceivable but highly unlikely that inhaled, ingested, or injected radionuclides could produce large doses over a short time, it is much more likely that acute exposures from a terrorist attack (e.g., with a dirty bomb) would come from external gamma radiation. 

Artificial radionuclides Radionuclides produced by humans via the explosion of atomic bombs and in nuclear reactors. 

Impulse marker the subsurface peak of maximum activity of a radionuclide that was produced during a specific time period in the atmosphere (e.g., 137Cs during bomb testing) and can used to measure accumulation rates. 

Similarly, 1 is a naturally occurring, cosmo-genic, and hssiogenic isotope T ri = 15.7 Myr Fabryka-Martin et al., 1991 FabrykaMartin, 2000). Like H, and C1, was produced in bomb tests, but in greater abundance above the natural level. While some of the other anthropogenic radionuclides have returned to near pre-bomb levels in the surface environment, the level continues to be elevated due to emissions from... 

Actinides in the environment can be classified into two groups (i) the uranium and thorium series of radionuclides in the natural environment and (ii) neptunium, plutonium, americium and curium which are formed in a nuclear reactor during the neutron bombardment of uranium through a series of neutron capture and radioactive decay reactions. Transuranics thus produced have been spread widely in the atmosphere, geosphere and aquatic environment on the earth, as a result of nuclear bomb tests in the atmosphere, and accidental release from nuclear facilities (Sakanoue, 1987). Most of these radionuclide inventories have deposited in the northern hemisphere following the tests conducted by the United States and the Soviet Union. 

The primary source of radionuclides produced in the fission process and found in the environment is atmospheric testing of nuclear weapons. The public has been exposed to these and other radionuclides for five decades, but there has been a substantial decline in atmospheric testing in the past two decades. Therefore the major source of fission product radionuclides in recent years has been from nuclear accidents. A nuclear reactor meltdown could release a spectrum of radionuclides similar to that of a nuclear bomb explosion, but the ratios of nuclides would greatly differ for the two cases. The reason for the differences in ratios of radionuclides is that during the reactor operation the long-lived radionuclides tend to build up progressively, whereas the... 

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