Radioactive particle

Atoms with the same number of protons but a different number of neutrons are called isotopes. To identify an isotope we use the symbol E, where E is the element s atomic symbol, Z is the element s atomic number (which is the number of protons), and A is the element s atomic mass number (which is the sum of the number of protons and neutrons). Although isotopes of a given element have the same chemical properties, their nuclear properties are different. The most important difference between isotopes is their stability. The nuclear configuration of a stable isotope remains constant with time. Unstable isotopes, however, spontaneously disintegrate, emitting radioactive particles as they transform into a more stable form. 

The most important types of radioactive particles are alpha particles, beta particles, gamma rays, and X-rays. An alpha particle, which is symbolized as a, is equivalent to a helium nucleus, fHe. Thus, emission of an alpha particle results in a new isotope whose atomic number and atomic mass number are, respectively, 2 and 4 less than that for the unstable parent isotope. 

An instrument for counting radioactive particles based on their ability to ionize an inert gas such as Ar. 

Direct Analysis of Radioactive Analytes The concentration of a long-lived radioactive isotope is essentially constant during the period of analysis. As shown in Example 13.6, the sample s activity can be used to calculate the number of radioactive particles that are present. 

For example, when the activity is determined by counting 10,000 radioactive particles, the relative standard deviation is 1%. The analytical sensitivity of a radiochemical method is inversely proportional to the standard deviation of the measured ac-... 

Selectivity rarely is of concern with radiochemical methods because most samples contain only a single radioactive isotope. When several radioactive isotopes are present, differences in the energies of their respective radioactive particles can be used to determine each isotope s activity. 

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. 

Activity The nature of the work carried out by a person, measured in Met units. Also, the decay rate of radioactive particles. 

Radioactive particle tracking (RPT) can be used to map the velocity field by tracking the position of a single radioactive tracer particle in a reactor. The particle which may consist of a polypropylene shell contains a radionuclide that emits y-rays. 

Direct measurement of particle velocity and velocity fluctuations in fluidized beds or riser reactors is necessary for validating multiphase models. Dudukovic [14] and Roy and Dudukovic [28] have used computer-automated radioactive particle tracking (CARPT) to foUow particles in a riser reactor. From their measurements, it was possible to calculate axial and radial solids diffusion as well as the granular temperature from a multiphase KTGF model. Figure 15.10 shows one such measurement... 

Particulates heavy metals, volatile organic compounds pesticides radioactive particles... 

As indicated above, there is a relationship between particle concentration, equilibrium factor and the amount of highly mobile radioactive particles. Removal of the accumulation mode particles may decrease the decay product exposure, but increase the dose because of the high effectiveness of the "unattached activity in dose deposition. Thus, air cleaning may not succeed in lower risk unless both factors are taken into account. Jonassen explores electrostatic filtration in this context. Finally, design considerations are presented for a possible alternative control system using activated carbon in an alternating bed system. 

When air is passed through a filter, be it electro- or mechanical, airborne, inactive as well radioactive, particles are removed with... 

Data on the rate of attachment or deposition, i.e., plate-out of radioactive particles on walls can be used to calculate the particle deposition velocity. Deposition rates can be determined experimentally by measuring the surface activity on some samples... 

The environmental conditions for each of the cases considered below are summarized in Table III all these parameters are constant in time. The build up of the nucleation mode of the stable particles and the build up of both the nucleation and accumulation modes of the radon decay products is calculated, and the results are given after a process time of one hour. Figures 1 to 5 show the size distributions of stable and radioactive particles, and Table IV gives the disequilibrium, the equilibrium factor F, the "unattached fraction" f and the plate-out rates for the different daughters. 

Radon-222, a decay product of the naturally occuring radioactive element uranium-238, emanates from soil and masonry materials and is released from coal-fired power plants. Even though Rn-222 is an inert gas, its decay products are chemically active. Rn-222 has a a half-life of 3.825 days and undergoes four succesive alpha and/or beta decays to Po-218 (RaA), Pb-214 (RaB), Bi-214 (RaC), and Po-214 (RaC ). These four decay products have short half-lifes and thus decay to 22.3 year Pb-210 (RaD). The radioactive decays products of Rn-222 have a tendency to attach to ambient aerosol particles. The size of the resulting radioactive particle depends on the available aerosol. The attachment of these radionuclides to small, respirable particles is an important mechanism for the retention of activity in air and the transport to people. 

The ionic charge, diffusivity, and electrical mobility associated with these small radioactive particles are three parameters controlling plateout. A particle can acquire an electrical charge by a number of mechanisms which promote the transfer of electrons to and from the particle surface, therefore producing a negatively and positively charged particle, respectively. With the decay of Rn-222, an alpha particle and Po-218 are formed. As these... 

Chamberlain, A.C., Megaw, M.J. and Wiffen, R.D., Role of Condensation Nuclei as Carrier of Radioactive Particles, Geofisica pura e applicata, 36 233-242 (1957). 

Fig. 2a. Pulmonary and lymph node burdens of inhaled radioactive particles for Class W and Class Y compounds (no radioactive decay) as projected from the TGLD clearance model.

When high-specific-activity, non-colloidal preparations are administered (a) they are partitioned characteristically between liver and bone (b) in rodents the rate of loss of the liver burden is high (halftime = 6.5 to 10.8 d) (Durbin, 1973) (c) the spleen content is low and (d) autoradiographs show uniform distribution in hepatic cells rather than of phagocytosis of radioactive particles in the reticuloendothelial cells of the liver, spleen, and bone marrow, and there is deposition on bone surfaces. 

Cloud Chambers A chamber containing air saturated with vapor is used. Radioactive particles ionize air molecules in the chamber. Cooling the chamber causes droplets of liquid to condense on these ions, giving observable fog-like tracks. 

Excitation of sample by bombardment with electrons, radioactive particles or white X-rays. Dispersive crystal analysers dispersing radiation at angles dependent upon energy (wavelength), detection of radiation with gas ionization or scintillation counters. Non-dispersive semiconductor detectors used in conjunction with multichannel pulse height analysers. Electron beam excitation together with scanning electron microscopes. 

Equation (9.6) is the basic equation describing the decay of all radioactive particles, and, when plotted out, gives the familiar exponential decay curve. The parameter X is characteristic of the parent nucleus, but is not the most readily visualized measure of the rate of radioactive decay. This is normally expressed as the half life (7/ 2). which is defined as the time taken for half the original amount of the radioactive parent to decay. Substituting N = Na/2 into the Equation (9.6) gives ... 

It is highly improbable that a nuclear fission power plant would ever explode like a nuclear bomb, but a loss of coolant accident could result in a melt down condition. In a melt down, a large amount of radiation can be released at ground-level. A nuclear or conventional chemical or steam explosion could disperse much of the radioactive particles into the atmosphere. This is essentially what happened when the Chernobyl gas explosion occurred in the Soviet Union in 1986. 

While nuclear power plants use multiple layers of protection from the radioactive particles inside the reactor core, a serious accident can cause the release of radioactive material into the environment. It is not a nuclear explosion, because the uranium fuel used in a nuclear power plant does not contain a high enough concentration of U-235. For an explosion to occur, the uranium fuel inside the reactor would have to be enriched to about 90% U-235, but it is only enriched to about 3.5%. 

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