Radioactive cloud

Ground radiation is from deposited radioactive particles. The deposition rate from a radioactive cloud without rain (dry deposition) is so low that the ground radiation dose is about the same as the inhalation dose. A heavy rain, however, may wash out enough particles from the plume to make ground radiation the dominant contributor to the total dose in a limited area. Rain will also attenuate radiation by leaching the radioactivity to be shielded by the soil and by moving it to streams for further removal. 

Integration of the specific activities over the particle size yields a much lower amount of 90Sr than of 147Pm produced, even if estimates from analyses of particles greater than 100/x are included (7). Such a result suggests that the sample was not representative of the true radioactive cloud distribution. 

The detailed structure of the radioactive cloud after stabilization has occurred (within 10 minutes) has not been studied extensively. Figure 2 shows some relative radiation intensity data obtained by rockets following the Zuni explosion (3.5-megatons, coral island surface). The data pertain to the situation 15 minutes after the explosion. The evidences of a toroidal structure are still marked. Note that the bulk of the radioactivity is in the core of the cloud and that the distribution, either horizontally or vertically, is far from uniform. The aircraft samples on Zuni were collected at 41 kft., well below the core of concentration as found at 15 minutes. Since only the lower fringes of the nuclear cloud were penetrated, analyses probably do not represent fairly the nuclear cloud as it existed at the time of sampling. 

Stewart, N.G. Crooks, R.N. (1958) Long range travel of the radioactive cloud from the accident at Windscale. Nature, 182, 627-30. 

C In 1986. an explosion at Chernobyl in the Ukraine released a radioactive cloud... 

Keeping your skin, nose, and mouth covered as you move out of the path of the radioactive cloud can provide some additional protection, but do this only if it causes no more than a few moments delay in evacuating the fallout zone or finding shelter. Once you have protected yourself from the fallout, you should decontaminate yourself as described earlier. 

Even those who are located outside the fallout zone should take shelter, preferably in the basement of a house or building, given the uncertainties about exactly where the radioactive cloud will travel. 

The explosion bombed a mile-wide crater in the island site, and a radioactive cloud rose ten miles and reached a diameter... 

At first it was necessary to process by chemical methods the material obtained from filter papers which had been flown through the radioactive cloud by the drone planes. 

PAR Coordinates of external contours of radioactive cloud N/A Six-digit coordinates. Letter R identifies RADAR set. 

PBR Downwind direction of radioactive cloud and unit of measure N/A Deg magnetic north (DGM) or mils (MLM). Deg true north (DGT) or mils (MLT). Deg grid north (DGG) or mils (MLG). Letter R identifies RADAR set. 

The reality of radioactive contamination of the environment was brought home to the world by the Chernobyl accident, which occurred on 26th April 1986. Radioactive clouds were produced and blown on the wind over large parts of Europe and Asia (IAEA, 1986). 

The flow rate F of rivers and streams can be measured by injection of a radionuclide and measurement of the time for its arrival at detectors placed downstream. Because of turbulence the radioactive "cloud becomes quite diffuse. Therefore a more efficient technique called "total count is used. A known amount (/4q) of the radionuclide is injected into the river and a downstream detector registers a total count (R f as the radioactivity passes the faster it passes, the lower is the measured radioactivity. Thus... 

Potassium iodide, also called KI, only protects a person s thyroid gland from exposure to radioactive iodine. KI will not protect a person from other radioactive materials or protect other parts of the body from exposure to radiation. It must be taken prior to exposure (for example, if people hear that a radioactive cloud is coming their way) or immediately after exposure to be effective. Since there is no way to know at the time of an incident whether radioactive iodine was used in the explosive device, taking KI would probably not be beneficial.Also, KI can be dangerous to some people. Taking KI is not recommended unless there is a risk of exposure to radioactive iodine. 

The Food and Drug Administration (FDA) recommends that KI be taken as soon as the radioactive cloud containing iodine from the explosion is close by. KI may still have some protective effect even if it is taken 3 to 4 hours after exposure to radioactive iodine. Because the radioactive iodine will be present in the initial blast and decays quickly, a single dose of KI may be all that is required. The FDA recommendations on KI can be reviewed on the Web at http //www.fda.gov/cder/guidance/4825fnl.htm. 

N. G. Stewart and R. N. Crooks. Long-range travel of the radioactive cloud from the accident at Windscale. Nature (London) 182, 627 (1958) A, C. Chamberlain and H. J. Dunster, Deposition of radioactivity in North-West England from the accident at Wind-scale. Nature (London) 182,629 (1958) H. J. Dunster, H. Howells, and W. L. Templeton, District surveys following the Windscale incident October 1957. Proc. U.N. Int. Conf. Peaceful Uses At. Energy, 2nd., Geneva Pap. 319 (1958). 

This method does not take into account the shielding effect of the ground roughness, nor the dimensions of the initial radioactive cloud. These effects, given the largely indicative character of these estimates, are to be considered as secondary. 

Rain or snow are much more important than these effects on the distribution of the contamination by causing a washout of the radioactive cloud and a patchy distribution of the unit dose. 

---