Debris fallout

It is possible to prepare very heavy elements in thermonuclear explosions, owing to the very intense, although brief (order of a microsecond), neutron flux furnished by the explosion (3,13). Einsteinium and fermium were first produced in this way they were discovered in the fallout materials from the first thermonuclear explosion (the "Mike" shot) staged in the Pacific in November 1952. It is possible that elements having atomic numbers greater than 100 would have been found had the debris been examined very soon after the explosion. The preparative process involved is multiple neutron capture in the uranium in the device, which is followed by a sequence of beta decays. Eor example, the synthesis of EM in the Mike explosion was via the production of from followed by a long chain of short-Hved beta decays,... 

Denmark 1.5 days after the explosion. Air samples collected at Roskilde, Denmark on April 27-28, contained a mean air concentration of 241Am of 5.2 pBq/m3 (0.14 fCi/m3). In May 1986, the mean concentration was 11 pBq/m3 (0.30 fCi/m3) (Aarkrog 1988). Whereas debris from nuclear weapons testing is injected into the stratosphere, debris from Chernobyl was injected into the troposphere. As the mean residence time in the troposphere is 20-40 days, it would appear that the fallout would have decreased to very low levels by the end of 1986. However, from the levels of other radioactive elements, this was not the case. Sequential extraction studies were performed on aerosols collected in Lithuania after dust storms in September 1992 carried radioactive aerosols to the region from contaminated areas of the Ukraine and Belarus. The fraction distribution of241 Am in the aerosol samples was approximately (fraction, percent) organically-bound, 18% oxide-bound, 10% acid-soluble, 36% and residual, 32% (Lujaniene et al. 1999). Very little americium was found in the more readily extractable exchangeable and water soluble and specifically adsorbed fractions. 

Nishita, H. and Larsen, K. H. (1957). Summary of Certain Trends in Soil-Plant Relationship Studies of the Biological Availability of Fallout Debris, Report No. UCLA-401 (National Technical Information Service, Springfield, Virginia). 

Noyce, J. R., Moore, D. T., Sherwood, J. D., Daniel, P. R., Beck, J. N. and Kuroda, P. K. (1973). Fallout from nuclear weapons testing and interhemispheric transport of nuclear debris, Health Phys. 25, 109. 

Time and shielding can be merged into a single factor. The shelters described in Section 5.2.1 (walls, basements, etc.) really serve as shields from radiation, heat, fallout, and even from the air blast and flying debris. At the moment of explosion, radiation and heat travel at the speed of light and expose unshielded victims. At the instant of realization that a nuclear weapon has exploded, an individual should move as quickly as possible to a location behind a rugged shielding material. 

The intense initial heat lasts several seconds and the initial radiation lasts only a few minutes. Seek shelter behind some solid barrier (i.e., a brick wall or subway tunnel) as soon as possible to avoid high radiation doses and thermal burns. Hopefully, this solid barrier will also be able to endure the coming air blast. An air blast from a nuclear explosion travels at approximately 5 miles per second and carries with it glass, metal, or any debris in its path. By immediately retreating behind a solid barrier, individuals can avoid exposure to the initial heat and radiation and hopefully survive the air blast. The next challenge is seeking long-term shelter to avoid the radiation from fallout. 

The team should record the accumulation of soot or airborne fallout debris and the overall deposit pattern. The investigators should also note irregularities, skips, or absence of soot or fallout, especially when there is an anomaly in the pattern. If there are differences in depth, color, pattern, or appearance, these differences should be noted, examined, analyzed, and photographed. 

Inspection of the site and an assessment of the wind direction enables an informed judgement to be made regarding the position of the fireworks in relation to the spectators. If necessary, the positions must be adjusted (or even reversed) so that members of the audience have their backs to the wind so far as is possible. It is absolutely vital that smoke and debris do not drift towards the audience. If necessary maximise the distance from the audience for fallout remove items from the display or cancel the display. 

But for chemists, the hydrogen bomb tests had a happier fallout too. Scientists at the Mike test collected coral from a nearby atoll contaminated with radioactive debris, and sent it to Berkeley for analysis. There the nuclear chemists found two new elements, with atomic numbers 99 and 100. They were named after two of the century s most creative physicists einsteinium and fermium. 

The half-life of 244Pu (8.2 X 107 years) is short compared with the age of the earth (4.5 X 109 years), and hence this nuclide is now extinct. However, the time interval (a) between the element synthesis in stars and formation of the solar system may have been comparable with the half-life of 244Pu. It has been found recently in this laboratory that various meteorites contain excess amounts of heavy xenon isotopes, which appear to be the spontaneous fission decay products of 244Pu. The value of H calculated from the experimental data range between 1 to 3 X 108 years. The process of formation of the solar system from the debris of supernova is somewhat analogous to the formation of fallout particles from a nuclear explosion. 

The eastward movement of the nuclear debris injected into the atmosphere at Lop Nor (90°E and 40°N) can be computed as shown in Figure 3 (10). Whenever the fresh nuclear debris completes one cycle around the earth, there is usually a sudden increase in the concentrations of short lived isotopes such as 33-day 141Ce, 50.4-day Sr, 65-day 95Zr, as well as the number of single fallout particles in the unit volume of air, as shown in Figures 4 and 5 (1, 16,17). 

Table II summarizes some of the features of the radioactive fallout processes in geophysical and astronomical settings. It seems that similarities do exist between the processes of formation of single particles from nuclear explosions and formation of the solar system from the debris of supernova explosion. We may be able to learn much more about the origin of the earth, by further investigating the process of radioactive fallout from the nuclear weapons tests.

Cs occurs in crater ejecta and fallout debris as a surface-adsorbed, soluble radionuclide, owing to its gaseous precursor. The behavior of... 

Mechanisms and rates of transport of nuclear test debris in the upper and lower atmosphere are considered. For the lower thermosphere vertical eddy diffusion coefficients of 3-6 X 106 cm.2 sec. 1 are estimated from twilight lithium enhancement observations. Radiochemical evidence for samples from 23 to 37 km. altitude at 31° N indicate pole-ward mean motion in this layer. Large increases in stratospheric debris in the southern hemisphere in 1963 and 1964 are attributed to debris from Soviet tests, transported via the mesosphere and the Antarctic stratosphere. Most of the carbon-14 remains behind in the Arctic stratosphere. 210Bi/ 210Pb ratios indicate aerosol residence times of only a few days at tropospheric levels and only several weeks in the lower stratosphere. Implications for the inventory and distribution of radioactive fallout are discussed. 

It was pointed out above that the 18r W tracer observations, the excess 210Pb in the tropical stratosphere, and the radiochemical evidence from fallout samples collected by balloon can be reconciled with the slow mean motion of air upward across the equatorial tropopause and within the tropical stratosphere and outward toward higher latitudes at stratospheric levels up to about 35 km. Above 23 km. altitude, such mean motions poleward can explain the lack of significant equatorwards transport of fallout debris from Novaya Zemlya. In the stratosphere, below 23 km., meridional eddy mixing obscures the pattern of slow mean motions. However, even in this layer, little Soviet test debris mixes south of about 30 °N, suggesting that poleward mean motions restrict equator-wards transport by eddy mixing within the lower stratosphere between the equator and 30 °N. 

The spectrometer has also been applied successfully to the counting of environmental samples contaminated with worldwide fallout, reactor effluent, and debris from nuclear cratering experiments. In addition, it has been possible to carry out a variety of laboratory experiments not practical in the past because of the need for laborious radiochemical analysis such experiments have involved the analysis of several hundred samples each containing up to 20 isotopes. 

TU any of the less-understood phenomena leading to the observed fall-out distribution resulting from a nuclear explosion occur on a relatively short time scale (a few tens of seconds or less). These short term phenomena lead to an initial distribution of radioactive material referred to as the source term in a fallout study. Many predictive calculations are based on an assumed source term, which of necessity has been quite oversimplified. Two typical simplifications made for purposes of model development are (1) that the radiochemical composition of fallout is well defined and uniform (2) that the particles comprising the initial debris are uniform with respect to settling rate in the atmosphere. The latter assumption has received considerable attention elsewhere, notably in the work of Miller (2). However, the former assumption concerning the radiochemical uniformity of the debris has received far less systematic attention. 

This technique has been applied to data from a set of 42 samples from a nuclear detonation. Samples were taken both from fallout collectors and from airborne-debris samplers. Twenty-seven radionuclides could be identified and measured with acceptable precision (better than 10% ) in at least some of the samples. The results are presented in Table I. This calculation was performed without the added variance term Fik. The nuclides include both fission and activation products. 

Data relating to radionuclide deposition (fallout) within a few miles of the Danny Boy, Sedan, and Palanquin nuclear cratering shots are examined for evidence of fractionation. The fractionation index is computed for several fission-product mass chains produced in each event. For the three events studied only Danny Boy showed unambiguous evidence of fractionation in the early fallout, and the degree of fractionation was small. In Danny Boy there was only a factor of four difference between most enriched and most depleted species, compared with the factors of several hundred that have been observed in many late time samples of airborne debris. If this small amount of fractionation proves to be true in general for cratering shots, predictions of early-fallout gamma-radiation patterns will be simplified. 

Table I. Calculated Fractionation Indices for Early Fallout Debris from the Danny Boy, Sedan, and Palanquin Nuclear Cratering Shots...

For Danny Boy the indices are roughly four times as high for the volatiles as for the nonvolatiles, while the intermediates fall between these extremes. This clear-cut, systematic difference in the indices is taken as evidence that fractionation occurred in the Danny Boy early fallout but to a much smaller degree (factor of four) than might have been predicted on the basis of other fractionation studies. (For example, late time samples of airborne debris have shown fractionation involving factors of several hundred.)... 

Figure 15 shows the close-in fallout collection array (NRDL) and the radiation pattern at 1 hour. The first three numbers of the close-in samples correspond to the numbers of the stations shown here. The letters AO and PC indicate always-open collectors and platform collectors, respectively. These collectors were identical, but the PC collectors received better protection from dust prior to shot time. The next number indicates which of the 9 or 16 pans in the array has been taken. Additional numbers indicate sieve sizes retaining the debris. 

Fractionation correlation techniques have been applied to cloud, fallout, and ground-filter samples from the Transient Nuclear Test of January 1965. Although safety analysts do not consider fractionation effects to be of operational importance for this type of event, analysis of such data provides insight into the mechanisms of debris formation. The results show many similarities to the correlations observed for fallout. Those dissimilarities found indicate the importance of escape processes to the formation mechanisms for this type of debris. 

Although the transient test was orders of magnitude below a nuclear weapon in regard to energy release and temperature achieved, the debris showed many similarities to fallout. These included not only the size and appearance of the particles but also the correlation properties of various radionuclides. Dissimilarities in the correlations and the variation of specific activity with particle type confirm expectations of the importance of escape processes to the formation mechanisms for this type of debris. This study shows that data-correlation techniques developed for fallout characterization are also useful in studying reactor debris. 

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