Decay continued

The nature of the radioactive decay is characteristic of the element it can be used to fingerprint die substance. Decay continues until bodi die original element and its daughter isotopes are non-radioactive. The half-life, i.e. die time taken for half of an element s atoms to become non-radioactive, varies from millions of years for some elements to fractions of a second for odiers. 

A sample of any unstable nuclide undergoes nuclear decay continuously as its individual nuclei undergo reaction. All nuclear decays obey the first-order rate law Rate = C. This rate law can be treated mathematically to give Equation, which relates concentration, c, to time, t, for a first-order process (Cq is the concentration present at... 

C22-0012. Radioisotopes are used in many research applications. Because they decay continuously, the shelf life... 

Figure 31 compares the dynamic structure factors obtained from the crosslinks and the chain ends for two different Q-values. Without any analysis a strong reduction of the cross-link mobility compared to that of the chain end is obvious. A closer inspection also shows that the line-shape of both curves differs. While S(Q,t)/S(Q, 0) from the chain end decays continuously, S(Q,t) from the cross-links appears to decay faster at shorter than at longer times. This difference in line shape is quantified via the line shape parameter p. For the end-labelled chains, p is in close agreement with the p = 1/2 prediction of the... 

In the absence of the SLR processes, the value of this ratio would depend on the mode of preparation of the triplet state. Three extreme cases could be realized, in the first case, the system is being continuously excited and decays continuously, i.e., the system is in a steady state. By equating the rates of pumping of any zf level with its rate of decay, one obtains the following ratios ... 

Radioactive decay rates are measured in half-lives. A half-life is the time required for one-half of a radioisotope s nuclei to decay into its products. For example, the half-life of the radioisotope strontium-90 is 29 years. If you had 10.0 g of strontium-90 today, 29 years from now you would have 5.0 g left. Table 25-4 shows how this decay continues through four half-lives of strontium-90. Figure 25-13 presents the data from the table in terms of the percent of strontium-90 remaining after each half-life. 

SO2 decays continuously with time, while that of SO3 reaches a maximum and than falls again. At any time, the amounts ofS02(g) and S03(g) will determined by the ratio of sulfite sulfate deposited (Bunce, 1994). 

In this expression, c = yy Fjf/Ytotj This limiting case was observed for anthracene in about the first 4 ms after the end of the excitation [48]. In the further course of the decay of the triplet excitons, the relative fraction of the bimolecular decay continues to decrease until the limit of long times is reached, in which the monomolecular decay predominates (fer[Ti > ot [Ti] ). The solution of Eq. (6.30) is then given by [Ti] = [Ti]ooe r . With this and Eq. (6.33b), the decay of the delayed fluorescence in the hmit of very small triplet exciton concentration, i.e. in the later part of the decay curve, is found to be... 

Some nuclei cannot gain stability by a single emission. Consequently, a series of successive emissions occurs as shown for uranium-238 in A FIGURE 21.3. Decay continues until a stable nucleus—lead-206 in this case—is formed. A series of nuclear reactions that begins with an unstable nucleus and terminates with a stable one is known as a radioactive series or a nuclear disintegration series. Three such series occur in nature uranium-238 to lead-206, uranium-235 to lead-207, and thorium-232 to lead-208. 

At the time the active uranium rods are placed in the coffin 148, they are disposed under water and are thus cooled and shielded. After the coffin is filled, it is raised to the top of the shield water 65 and removed to an 2o aging pit, not shown, and placed under water where the radioactive decay continues. Means for cooling the rods must be provided during this removal, and for present purposes, since the coffin, per se, forms no part of the invention, it will suffice to say that the cooling can be effected 30 by circulating cooling water through the coffin from an outside water supply in any well known manner. 

A Figure 21.3 Nuclear decay chain for uranium-238. The decay continues until the stable nucleus is formed. 

Certain isotopes are unstable Their nucleus breaks apart, undergoing nuclear decay. Sometimes the product of that nuclear decay is unstable itself and undergoes nuclear decay, too. For example, when U-238 (one of the radioactive isotopes of uranium) initially decays, it produces Th-234, which decays to Pa-234. The decay continues until, finally, after a total of 14 steps, Pb-206 is produced. Pb-206 is stable, and the decay sequence, or series, stops. 

Radionuclide generators are loaded by the manufacturer with a mother radionuclide. This radionuclide decays continuously to a daughter radionuclide with suitable properties for the preparation of radiopharmaceuticals. These generators can be used on site for a period of a week to several months, depending on the type of generator [1,2]. 

The sinusoidal surface is stable or unstable, depending on whether a grows indefinitely with time or decays continuously with time. The value of the wavelength A discriminating between these two possibilities is that value... 

Plutonium 239 decays continuously at a rate of 0.00284% per year. If X is the time a randomly chosen plutonium atom will decay, use the associated probability density function to compute the probability that a plutonium atom will decay between 100 and 500 years from now. 

Protactinium-234 is also radioactive, decaying to U-234 via beta emission. Radioactive decay continues until a stable nuclide, Pb-206, is reached. Figure 19.6 illustrates the entire uranium-238 decay series. 

Atoms of elements are composed of protons, neutrons, and electrons. Only certain combinations of protons and neutrons yield stable nuclides all other combinations are unstable. Radioactive decay is the process in which an unstable nucleus either ejects or captures particles transforming the radioactive nuchde into another element. In some cases the daughter nuchde produced by radioactive decay also is unstable and radioactive decay continues through as maity steps as necessary to prodnce a stable nuclide. 

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