In its natural state, at room temperature, polonium is a solid metal with a silver color. Polonium is one of 25 known radioactive isotopes of polonium. Purified polonium is very volatile, and polonium isotopes are radioactive. The most common and best-known polonium isotope is polonium This material is highly dangerous, but it has a relatively short half-life.
As a result, it ceases to be dangerous relatively quickly. It decays into a new, stable metal: lead. Its physical half life is days. This means that half its radioactivity dies away in this time. Its biological half life is 40 days , so it takes 40 days for biological processes to eliminate half of the Polonium in the body. Polonium is present in small amounts in the human body, due to low levels in the normal environment and the food chain, especially in seafood.
Tobacco smokers have more polonium because smoking causes it to accumulates in the lungs. Polonium is used in industry to make devices that remove static.
This is useful for making tape, rolling paper, and spinning synthetic fibers, for example. It is also used to keep environments dust free, such as in the production of computer chips.
Natural polonium is very rare. As little as about micrograms 0. There are very low levels of polonium in the environment, and it enters our bodies through the food chain, for example, when eating seafood.
These environmental levels are normally harmless to human health, except in smokers, who have higher levels. As a weapon, it would be lethal. But it is also extremely difficult to obtain. When used in commercial devices, this is done in such a way that the polonium could not be separated for use as a poison. If the RBE of Pu were 10 times the present value, there is a better than even chance that one of these five would have gotten bone cancer, but none did.
As our calculated inhalation effects are dominated by lung cancer, a factor of 10 increase in bone cancer risk would only double the total inhalation risk. Wolfe, and employee of a Nader-sponsored group, drew far-reaching conclusions from the fact that 11 of the first 30 deaths in the US Transuranic Registry a registry of people who have worked with plutonium revealed cancers on autopsy, whereas based on listed cause-of-death for all U.
His paper, which was never published in the scientific literature, received very wide publicity in the news media. However, it turned out that autopsies were done preferentially on people who had died of cancer, and that explained the entire effect. In addition, it was pointed out that Pu is expected to cause cancers of the lung, bone, and liver, whereas among the 11 cases there were no bone or liver cancers, and less than the expected number of lung cancers for a normal population.
Needless to say, the news media never bothered to report that the Wolf paper was based on an incorrect premise. In evaluating all of the criticisms outlined above, it is important to realize that they are actively considered every year by a committee of the ICRP and that they have repeatedly been rejected.
Likewise, the EPA, which has jurisdiction in the U. No standard-setting or official study group in any country has given credence to any of these criticisms of the standard procedures we used in deriving Table I. It is clear from Table I that Pu is dangerous principally as an inhalant, so we now consider the consequences of a dispersal of Pu powder in a populated area.
The calculations are done with a standard meteorological model, in which the dust cloud moves with the wind dispersing in the downwind, crosswind, and vertical directions. Meteorologists have determined the extent of dispersal as a function of wind velocity and atmospheric stability.
Figure 2 shows the results of calculations assigning the atmospheric stability most characteristic of each wind velocity. This is different between day and night, so separate curves are given for each. For example, we see from Fig. Similarly, from Fig.
As we know the cancer risk per microgram of Pu inhaled from Table I, it is straightforward to calculate the total number of cancers expected per gram of Pu dispersed. When corrections are applied for the fraction of typical Pu powders that are in particles of respirable size, the efficiency of dispersal, the protection afforded by being inside buildings, and decreased breathing rates at night, the result is that we may expect about one eventual cancer for every 24 g of Pu dispersed, or about 19 fatalities per pound.
If there is a warning, as in a blackmail scenario, people can be instructed to breathe through a folded handkerchief or a thick article of clothing, with a resulting decrease in fatalities to 3 per pound dispersed.
Eventually, the Pu settles to the ground but it may then be blown up by winds. Meteorologists have also developed methods for calculating these effects "deposition" and "resuspension". Within the first few months, this causes about one-third as many cancers as inhalation from the initial cloud. Beyond this time period, resuspension is of much less and continually decreasing importance as the Pu becomes part of the soil.
Of course, Pu lasts for tens of thousands of years, so let us consider its effects over this time period. We know the amount of uranium in soil and we know now how much there is as dust in the air, so we can estimate how much is inhaled per year -- it calculates out to be 1. If this factor is applied to the Pu after it becomes part of the soil, we find that over the 25,year half-life there will eventually be about one fatality per g of Pu dispersed.
Thus, we see that the long half-life is almost irrelevant; nearly all of the damage eventually done occurs very soon after dispersal. A summary of all these effects of Pu dispersal is given in Table II. It also includes plant uptake into food. There is a great deal of information on uptake of Pu by plants both from laboratory experiments and from several areas where an appreciable amount of Pu has gotten into the soil from bomb tests or from various research activities.
Plant uptake is small for the same reason that Pu does not easily pass through the walls of the intestines -- it forms large molecules, which do not easily pass through membranes. The views expressed are those of the author s and are not necessarily those of Scientific American.
Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital. But just how the body absorbed this toxic element remained a matter of speculation. Last week, the Japanese media criticised the video, which has been sent to local authorities throughout the country.
In response, the Power Reactor and Nuclear Fuel Development Corporation, which commissioned the ten-minute cartoon, says it will not send out any more copies. Pluto Boy explains that plutonium is not as dangerous as most people think.
So very little will contaminate the water. If the water is drunk, the plutonium will pass through the body and be flushed out.
0コメント