Sources of particles

Protons, deuterons, and helium ions. The most common sources of high energy protons up to 800 Mev are synchrocyclotrons. At the present time the three proton synchrotrons which produce protons of higher energy are the 

Albert Wattenberg Nuclear Reactions at High Energies. 

Birmingham machine (iXlO ev), the Brookhaven Cosmotron (3Xl0 ev), and the Berkeley Bevatron (6x10 ev). 

LeCouteurS has proposed a more efficient technique for obtaining external beams from synchrocyclotrons which has been quite successful. 

With an external proton beam both of these experimental sources of energy spread can be avoided. The type of neutron energy spectrum one obtains are illustrated by the measurements of Cassels et al. at 145 Mev, of Nelson et al. at 220 Mev, of Goodell et aL at 350 Mev and of Nedzel at 410 Mev. 

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Particle Attrition. Distributor jets are a potential source of particle attrition. Particles are swept into the jet, accelerated to a high velocity, and smash into other particles as they leave. To reduce attrition at distributors, a shroud or larger-diameter pipe is often added concentric to the jet hole, as shown in Figure 15. The required length of the concentric shroud is given by the relation... 

The secondary source of fine particles in the atmosphere is gas-to-particle conversion processes, considered to be the more important source of particles contributing to atmospheric haze. In gas-to-particle conversion, gaseous molecules become transformed to liquid or solid particles. This phase transformation can occur by three processes absortion, nucleation, and condensation. Absorption is the process by which a gas goes into solution in a liquid phase. Absorption of a specific gas is dependent on the solubility of the gas in a particular liquid, e.g., SO2 in liquid H2O droplets. Nucleation and condensation are terms associated with aerosol dynamics. 

Combustion processes are a major source of particles emitted to the atmosphere. Particles formed in combustion systems fall roughly into... 

Table II shows the nominal alpha dose factors for occupational mining exposure. Table III shows the alpha dose factors for the nominal environmental situation. Table IV shows the bronchial dose factors for the smallest sized particles, that dominated by the kerosene heater or 0.03 pm. particles. The radon daughter equilibrium was shifted to a somewhat higher value in this calculation because this source of particles generally elevates the particle concentration markedly with consequent increase in the daughter equilibrium. Table V shows the alpha dose for a 0.12 pm particle, the same as the nominal indoor aerosol particle, but for a particle which is assumed to be hygroscopic and grows by a factor of 4, to 0.5 pm, once in the bronchial tree.

Particle sinking rates are of considerable interest because the fester a particle can make the trip to the seafloor, the shorter the time it is subject to decomposition or dissolution and, hence, the greater its chances for burial in the sediments. The length of the trip is dictated by the depth to the seafloor, the horizontal current velocity, and the particle sinking rates. As shown in Figure 13.5, sedimentation rates decrease with increasing water depth. This relationship reflects the preservation issue and the feet that coastal waters tend to have larger sources of particles to the surfece zone. 

Earth s crust is a source of particles produced as a consequence of weathering and volcanic activity. Weathering of continental rocks generates terrigenous particles that are carried into ocean via rivers, glaciers, and winds. As shown in Table 13.2, the most abundant mineral types are quartz, plagioclase, and clay minerals. The most abimdant... 

In urban areas, the typical dominant sources of fine organic aerosol particles are diesel exhaust, gasoline-powered vehicle exhaust, meat cooking operations, smoke from wood combustion, and paved road dust followed by four smaller sources of particles tire wear, vegetative detritus, natural gas combustion, and cigarette smoke. ... 

Among the multivariate statistical techniques that have been used as source-receptor models, factor analysis is the most widely employed. The basic objective of factor analysis is to allow the variation within a set of data to determine the number of independent causalities, i.e. sources of particles. It also permits the combination of the measured variables into new axes for the system that can be related to specific particle sources. The principles of factor analysis are reviewed and the principal components method is illustrated by the reanalysis of aerosol composition results from Charleston, West Virginia. An alternative approach to factor analysis. Target Transformation Factor Analysis, is introduced and its application to a subset of particle composition data from the Regional Air Pollution Study (RAPS) of St. Louis, Missouri is presented. 

If we have determined m elements in n samples, we could display these results as n points in an m-dimensional space. However, because some of the elements are emitted by the same source of particles, their concentrations will be related. 

To illustrate this idea, suppose that we have two sources of particles, an iron foundry and automobile emissions, and that we measure three elemental concentrations, iron, lead, and bromine. 

Prior Applications. The first application of this traditional factor analysis method was an attempt by Blifford and Meeker (6) to interpret the elemental composition data obtained by the National Air Sampling Network(NASN) during 1957-61 in 30 U.S. cities. They employed a principal components analysis and Varimax rotation as well as a non-orthogonal rotation. In both cases, they were not able to extract much interpretable information from the data. Since there is a very wide variety of sources of particles in 30 cities and only 13 elements measured, it is not surprising that they were unable to provide much specificity to their factors. One interesting factor that they did identify was a copper factor. They were unable to provide a convincing interpretation. It is likely that this factor represents the copper contamination from the brushes of the high volume air samples that was subsequently found to be a common problem ( 2). 

Dispersion Normalization. Atmospheric dispersion is greater in winter than in summer in New York City and, in addition, varies from year to year. Thus, for a constantly emitting source of particles, atmospheric concentrations of TSP observed in winter would be lower than in summer. In order to relate ambient concentrations of particulate species to their sources Kleinman, et al. ( 5), suggested the use of a dispersion normalization technique based on the dispersion factor proposed by Holzworth ( ). Ambient concentrations of aerosol species are multiplied by the ratio of the dispersion factor for the sampling period to an average dispersion factor of 4200 m /sec. 

The sources of particles in the atmosphere are of much current interest. This is true from the viewpoint of both the geo-atmospheric scientist and the pollution control specialist. For the atmospheric chemist or geochemist, the identities and the relative contributions of sources are important for understanding 1) atmospheric element cycles and budgets, and 2) the chemical content of precipitation. 

The composition and sources of particles are discussed in detail in Chapter 9. Major natural sources of particles include terrestrial dust caused by winds, sea spray, biogenic emissions, volcanic eruptions, and wild-... 

Cass and co-workers (e.g., Rogge et al., 1996 Gray and Cass, 1998 Kleeman and Cass, 1998) have used this method to assess the contribution of various sources of particles in the Los Angeles area. If the particle emissions from each source are known and assumed to remain in air as external mixtures, they can be tracked separately in the model as they are transported and react. Hence their contribution to the concentrations at a particular location can be calculated. 

In summary, the use of mass spectrometric methods, combined with various approaches to vaporizing and ionizing the particles, is gaining increasing popularity and interest for the analysis of continuous sources of particles or single particles. The problem of quantification of the components seen by single-particle laser ionization techniques remains to be solved. On the other hand, the vaporization approaches can provide quantitative data on some volatile and semivolatile components but cannot measure the nonvolatile species and, at present, do not provide a full mass spectrum for a single particle. 

In general, if there are no indoor sources of particles, the levels indoors tend to reflect those outdoors. For example, application of a mass balance model to measurements of indoor and outdoor particle concentrations in Riverside, California, indicated that 75% of PM2S and 65% of PMI0 in a typical home were from outdoors (Wallace, 1996). Similar conclusions were reached by Koutrakis et al. (1991, 1992) for homes in two counties in New York. For example, they report that 60% of the mass of particles in homes is due to outdoor sources. However, the contribution to various individual elements in the particles varies from 22% for copper to 100% for cadmium. 

Kerosene heaters can be significant sources of particles under some circumstances. For example, kerosene heaters were reported to contribute to indoor PM2 5 in homes in Suffolk County, New York, but not Onondaga County wood stoves and fireplaces and gas stoves did not contribute in either case (Koutrakis et al., 1992 Wallace, 1996). A similar conclusion was reached in a study of eight mobile homes in North Carolina (Mum-ford et al., 1991). 

One basic difficulty with the nonlinear equation arises from the following. Consider a physical situation where a source of particles is composed of many emitters, each emitting a particle at a time. If considered alone, each particle would be described by a localized wave /,- solution of the master equation. Now, what happens if, instead of emitting the particles one by one, the source emits many particles at the same time If the master equation were a linear equation, like the usual Schrodinger equation, the answer would be trivial. The general solution would be simply the sum of all particular solutions. 

Of course, strictly speaking no stationary solution exists obeying (6.5) except P = 0. To overcome this objection one may imagine a source of particles near the bottom of the well, but it makes no difference as it does not enter the equation anyway. 

Source Identification of Airborne Particles, In recent years, ingenious methods of identifying the point source of airborne particles have been developed. If not specific point sources of pollution, rather small regional areas can often be identified. Source of particles can be important for numerous reasons, including the enforcement of regulation and also in sorting out. for example, the various distant sources that contribute to acid rain pollution. 

Although thermal (slow) neutrons derived from nuclear reactors are the most practical source of particles for nuclear excitation and generally provide the more useful reaction, other excitation sources, such as 14-MeV (fast) neutrons from commercially available accelerators or generators, have also been applied to coal analysis. 

Diesel engines, which are used in the larger vehicles, are important sources of particles and NOx, but emit relatively low amounts of CO and HCs. Diesel particulate emissions can, over time, be controlled. The control of NOx is problematic, and an appropriate technology is not available. Lean NOx catalysts are being pursued but conversion efficiencies remain low. 

Difusion Equation—We shall now proceed to discuss the general equations applying to a few special cases. Consider first a line source of particle emission in the ys-plane, at a height z above the xy-plane then any occurrence in the xz-plane through the line source will be the same in any other xz-plane. In other words, the problem is reduced to a two-dimensional analysis. If the particles are subject to a fluid velocity in the x-direction equal to vXi and if the particles are small enough that... 

The dynamical evolution of solids in protoplanetary disks is controlled by the large-scale flows that develop due to disk evolution, diffusion associated with the turbulence that is related to disk evolution or shear instabilities, gas-drag-induced motions due to different orbital velocities of the gas and solids, and settling towards the mid-plane due to the vertical component of the central star s gravity. As the large-scale flows have already been discussed, we now discuss the other sources of particle motions. 

Fig. 22 a, b. Tratumission electron micrographs of the samples used as sources of particles a) spin-cast with large particles, b) static-cast with small particles... 

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