Plutonium size distribution

To determine the effect of varying pH in the region of environmental interest on the plutonium size distribution, the latter was measured for plutonium solutions at an ionic strength of 0.01 pH of 5.4, 6.2, 6.9, and 8.2, shortly after pH adjustment, and also following 12 days of aging. 

To determine if bicarbonate has similar effects on the nature of the radiocolloid, the plutonium size distributions were studied at pH 7 as a function of bicarbonate concentration, using bicarbonate only from atmospheric CO.j and in solutions with [CH(V] equal to 10"2Af. The latter were prepared by adding NaHCOa. Two different ionic strengths were used to distinguish between the effects of added bicarbonate and ionic strength. The distributions of identical solutions which were shaken in flasks with and without granular silica were determined initially and... 

In the present paper the chemistry of plutonium is reviewed, with particular reference to the ambient conditions likely to be encountered in natural waters. In addition, experimental work is presented concerning the effects of such variables as pH, plutonium concentration, ionic strength, and the presence of complexing agents on the particle size distributions of aqueous plutonium. In subsequent papers it will be shown that these variables, as they influence the particle size distribution of the aqueous plutonium, greatly affect its interaction with mineral surfaces. The orientation of these studies is the understanding of the likely behavior and fate of plutonium in environmental waters, particularly as related to its interaction with suspended and bottom sediments. 

Further evidence of the effect of ionic strength on the plutonium colloidal system is shown in Figure 4, in which the size distribution of a 43-day old solution with an ionic strength of 0.002 is compared with a... 

The Coulter principle is also standard for dry toners [8,9] and an accepted method for aluminum oxide powder [10], chromatography media [11], polymeric powders [12], plutonium [13], filter evaluation [14], catalytic material [15] and comparing particle size distribution using alternative types of particle counters [16]. In ASTM method C-21 it states that the experience of several laboratories indicates that the method is capable of a repeatability of 1% and a reproducibility of 3% at the 95% confidence level. Operating procedures for this technique are also covered in BS3405 [17]. The method is also the subject of an international standard [18]. 

Somewhat different results were found in studies from the British Atomic Weapons Test Site at Maralinga, South Australia, where specific activities were noted to be greater in the soil size fractions >90 pm (Ellis and Wall, 1982). Presumably there are numerous factors that might influence the relationship of plutonium activity with soil particle size including the nature of the contaminating event, the degree of weathering since the contamination event, the chemical nature of the soil, and the particle size distribution of the soil. 

There are several isotopes of plutonium (Pu-238 and Pu-239 being the most important), and it is the chemistry of the isotopes that determines the reactions within the environment as well their transport and reactions within the body. Ingested plutonium is primarily excreted in feces, as there is very poor absorption from the gastrointestinal tract. For inhalation, the regional deposition pattern depends primarily on particle size distribution. Within the first few days, a fraction of the deposited activity is rapidly cleared from the respiratory tract. The remaining fraction is cleared slowly, with retention half-time of months to years, depending on the chemical form (oxides, for example, tend to be cleared more slowly than nitrates). Materials absorbed from the respiratory tract are primarily deposited in bone and liver, where it is retained for many years. A very small fraction may also be deposited in testes or ovaries. 

In one sorption experiment, the particle size distribution of the aqueous plutonium was determined by the centrifugation technique previously described (I). Simultaneously, a study was made of the size distribution of plutonium sorbed onto silica plates by an autoradiographic method (I, 2, 3). After the plutonium sorbed on the silica plates, the latter were dried and clamped for 2 to 4 days to glass plates coated with Kodak NTA nuclear emulsion. After developing the emulsion, the result-... 

Plutonium Particle Size Distributions. Pu particle size distributions were determined for an aqueous system sorbing onto silica plates. The initial Pu concentration was 1.5 X 10 7M, with a pH of 7.1 and ionic strength of 0.03M. Three silica plates were immersed in the solution and removed after sorption periods of 1, 5, and 17 days, respectively. When each plate was removed, aliquots of the solution were taken. Pu particle... 

Figure 5. Particle-size distributions for plutonium remaining in solution and that sorbed on silica plates at pH 7 and 0.03M ionic strength. The solid curves refer to the solution distributions.

Dust control. Small plutonium oxide particulates may become airborne and result in inhalation dose. Particulate size distribution at various stages and aerosol transport are subjects for careful study. Equipment and process designs can be used to control airborne particulate, such as setting up various pressure control zones in ventilation design, installing HEPA filtration systems, and installing area airborne particulate monitors. 

Plutonium is so toxic that processing and fabrication are always done in sealed cells or glove boxes, but accidental dispersion of aerosol occurs from time to time. Cheng et al. (2004) used a Lovelace Multi-jet cascade impactor for collecting aerosols during the release of an undetermined amount of Pu02 from a glovebox system, in a room within a Plutonium Facility (PF-4) at Los Alamos National Laboratory (LANL), Los Alamos, NM. They examined the plutonium particle activity size distribution. A plot of the aerodynamic size distribution and... 

Elder, J.C., Gonzales, M., Ettinger, H.J. (1974). Plutonium aerosol size characteristics. Health Phys. 27, 45-53. El-Hussein, A., Ahmed, A.A. (1995). Unattached fraction and size distribution of aerosol-attached radon prrgeny in... 

Although it is important to understand the mechanisms in the formation of the distribution of sizes among the colloidal plutonium hydroxide particles, the distributions themselves will influence the behavior... 

When a uranium or plutonium nucleus undergoes fission, it splits into two fragments of unequal size. Figure 2.1 shows yield/mass curves for fission of 235U and 239Pu by slow neutrons. Fission by fast neutrons gives slightly different distributions, with increased prob-... 

The particle size of a fission aerosol, and the distribution of fission products between particulate and vapour phases, depends on the mechanism of release to the atmosphere. In a weapons explosion, some physicochemical fractionation of radionuclides may occur, particularly if the explosion is near the ground. Everything in the vicinity is vapourised by the heat of the explosion, but within less than a minute the fireball cools to a temperature in the range 1000-2000°C, and refractory materials such as metal oxides and silicates condense to form particles (Glasstone Dolan, 1977). Refractory fission products, and plutonium, are incorporated in these particles. 

Cooper et al. (1994) have reported re-suspension studies on soils contaminated with plutonium during nuclear weapons tests by use of a mechanical dust-raising apparatus. Airborne dust was analysed in terms of mass and Am activities for particle sizes less than 7 pm. The AMAD was determined as 4.8-6 pm for re-suspended soil. Also, surface soil was characterised in the laboratory by means of sieving and microparticle classification, yielding mass and "Am activity distribution with respect to size. Data indicate the granularity of plutonium contamination at both major and minor trial sites. Depth profile analyses for undisturbed areas demonstrate that most (74% on average) of the americium and plutonium activity is found in the top 10 mm of soil. Plutonium and americium activities were found to be enhanced in the inhalable fraction over their values in the total soil, and the enhancement factors were similar in re-suspended dust and surface soil. Observed enhancement factors ranged from 3.7 to 32.5. 

The sorption and desorption of aqueous plutonium in the range of 10 7 to 10 8M was studied on quartz and other silica surfaces. Sorption continued typically for 12 to 15 days before apparent equilibrium was reached, and the distribution of plutonium particle sizes sorbed on the silica was different from that in solution. At pH 7, sorption increased with increasing ionic strength, but decreased when bicarbonate was added. The amount of sorption varied at pH 5 and 7, but differently at high and low ionic strengths, as well as with the age of the solution. Plutonium desorption indicated that there were two basically different sorbed species, and the rate and quantity of desorbed material increased at pH 5 compared with 7 and 9. 

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