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Half-life amount remaining

Although the nucleus of the uranium atom is relatively stable, it is radioactive, and will remain that way for many years. The half-life of U-238 is over 4.5 billion years the half-life of U-235 is over 700 million years. (Half-life refers to the amount of time it takes for one half of the radioactive material to undergo radioactive decay, turning into a more stable atom.) Because of uranium radiation, and to a lesser extent other radioactive elements such as radium and radon, uranium mineral deposits emit a finite quantity of radiation that require precautions to protect workers at the mining site. Gamma radiation is the... [Pg.866]

EXAMPLE 13.6 Using a half-life to calculate the amount of reactant remaining... [Pg.664]

For a first-order process, calculate the rate constant, elapsed time, and amount remaining from the half-life (Example 13.6 and Self-Test 13.9). [Pg.690]

Predict the amount of a radioactive sample that will remain after a given time period, given the decay constant or half-life of the sample (Example 17.3). [Pg.842]

As shown in Example, Equation is used to find a nuclear half-life from measurements of nuclear decays. Equation is used to find how much of a radioactive substance will remain after a certain time, or how long it will take for the amount of substance to fall by a given amount. Example provides an illustration of this t q)e of calculation. In Section 22-1. we show that Equation also provides a way to determine the age of a material that contains radioactive nuclides. [Pg.1570]

Dark Decay of UDMH in the Presence of NO, When 1.3 ppm of UDMH in air was reacted in the dark with an approximately equal amount of NO, 0.25 ppm of UDMH was consumed and formation of -0.16 ppm HONO and -0.07 ppm N2O was observed after -3 hours. Throughout the reaction, a broad infrared absorption at -988 cm" corresponding to an unidentified product(s), progressively grew in intensity. The residual infrared spectrum of the unknown product(s) is shown in Figure 2a. It is possible that a very small amount (50.03 ppm) of N-nitrosodimethylamine could also have been formed but the interference by the absorptions of the unknown product(s) made nitrosamine (as well as nitramine) detection difficult. No significant increase in NH3 levels was observed, in contrast to the UDMH dark decay in the absence of NO. Approximately 70% of the UDMH remained at the end of the 3-hour reaction period this corresponds to a half-life of -9 hours which is essentially the same decay rate as that observed in the absence of NO. [Pg.123]

Suppose the initial number of nuclei of a radioactive nuclide is N0, and that the half-life is T. Then the amount of parent nuclei remaining at a time t can be written as Nx = NQ( /2)(tlT>. This relationship is called the radioactive decay equation. What is the number of daughter nuclei present at time t, expressed in terms of N0 and Nx ... [Pg.193]

The area under the PCP concentration-time curve (AUC) from the time of antibody administration to the last measured concentration (Cn) was determined by the trapezoidal rule. The remaining area from Cn to time infinity was calculated by dividing Cn by the terminal elimination rate constant. By using dose, AUC, and the terminal elimination rate constant, we were able to calculate the terminal elimination half-life, systemic clearance, and the volume of distribution. Renal clearance was determined from the total amount of PCP appearing in the urine, divided by AUC. Unbound clearances were calculated based on unbound concentrations of PCP. The control values are from studies performed in our laboratory on dogs administered similar radioactive doses (i.e., 2.4 to 6.5 pg of PCP) (Woodworth et al., in press). Only one of the dogs (dog C) was used in both studies. [Pg.136]

The concept of half-life also applies to chemical reactions. The half-life of a chemical reaction is the time it takes for the amount of one of the reactants to be reduced by half. In some reactions the reaction rate is determined by the concentration of one particular reactant as the reaction proceeds and the concentration of this reactant decreases, so does the rate of the reaction. This is the case for example, with amino acids, the components of proteins. Amino acids may occur in one of two different forms, the / and d forms (see Textbox 24). In living organisms, however, the amino acids occur only in the / form. After organisms die, the amino acids in the dead remains racemize and are gradually converted into the d form. Ultimately, the remaining amino acid, which is then known as a racemic mixture, consists of a mixture of 50% of the / form and 50% of the d form. [Pg.74]

FIGURE 61 The decay of radiocarbon. Radiocarbon is a radioactive isotope whose half-life is 5730 + 40 years. This means that half of the original amount of radiocarbon in any carbon-containing sample will have disintegrated after 5730 years. Half of the remaining radiocarbon will have disintegrated after 11,400 years, and so forth. After about 50,000 years the amount of radiocarbon remaining in any sample is so small that older remains cannot be dated reliably. [Pg.299]

Statement (b) is correct. After each half-life—that is, after each 75 s—the amount of reactant remaining is half of the amount that was present at the beginning of that half-life. Statement (a) is incorrect the quantity of A remaining after 150 s is half of what was present after 75 s. Statement (c) is incorrect because different quantities of A are consumed in each 75 s of the reaction 1/2 of the original amount in the first 75 s, 1/4 of the original amount in the second 75 s, 1/8 of the original amount in the third 75 s, and so on. [Pg.318]

SAQ 8.18 The half-life of radioactive 14C is 5570 years. If we start with 10 g of 14C, show that the amount of 14C remaining after 11140 years is 2.5 g. [Pg.380]

A radioactive isotope may be unstable, but it is impossible to predict when a certain atom will decay. However, if we have a statistically large enough sample, some trends become obvious. The radioactive decay follows first-order kinetics (see Chapter 13 for a more in-depth discussion of first-order reactions). If we monitor the number of radioactive atoms in a sample, we observe that it takes a certain amount of time for half the sample to decay it takes the same amount of time for half the remaining sample to decay, and so on. The amount of time it takes for half the sample to decay is the half-life of the isotope and has the symbol t1/2. The table below shows the percentage of the radioactive isotope remaining versus half-life. [Pg.296]

If one knows the half-life and amount remaining radioactive, you can then use equation (2) to calculate the rate constant, k, and then use equation (1) to solve for the time. This is the basis of carbon-14 dating. Scientists use carbon-14 dating to determine the age of objects that were once alive. [Pg.297]

C—After one half-life, 50% would remain. After another half-life this would be reduced by A to 25%. The total amount decayed is 75%. Thus, 24.6 years must be two half-lives of 12.3 years each. [Pg.29]

Know that the half-life, ty2, of a radioactive isotope is the amount of time it takes for one-half of the sample to decay. Know how to use the appropriate equations to calculate amounts of an isotope remaining at any given time, or use similar data to calculate the half-life of an isotope. [Pg.267]

Plant In plants, the A-methyl group may be subject to oxidation or hydroxylation (Kuhr, 1968). The presence of pinolene (P-pinene polymer) in carbaryl formulations increases the amount of time carbaiyl residues remain on tomato leaves and decreases the rate of decomposition. The half-life in plants range from 1.3 to 29.5 d (Blazquez et al., 1970). [Pg.247]

Surface Water. In filtered lake water at 29 °C, 90% of 2,4-D (1 mg/L) mineralized to carbon dioxide. The half-life was <5 d. At low concentrations (0.2 mg/L), no mineralization was observed (Wang et ah, 1984). Subba-Rao et al. (1982) reported that 2,4-D in very low concentrations mineralized in one of three lakes tested. Mineralization did not occur when concentrations were at the picogram level. A degradation rate constant of 0.058/d at 29 °C was reported. At original concentrations of 100 mg/L and 100 pg/L in autoclaved water, the amount of 2,4-D remaining after 56 d of incubation were 81.6 and 79.6%, respectively (Wang et ah, 1994). [Pg.348]

Surface Water. In pond water, adsorption to suspended sediments was an important process. The initial half-life was reported to be no more than 68 d. After 120 d, 20% of the applied amount remained (Grzenda et al., 1966). The biodegradation half-life of amitrole in water is approximately 40 d (Reinert and Rodgers, 1987). [Pg.1549]

In the laboratory, half-lives ranged from 213-699 and 435-535 d at application rates of 60 and 10 kg/ha, respectively (Beck and Hansen, 1974). In anaerobic soils, the half-life of pentachloronitrobenzene was 21 d. After 3 wk of incubation, <1% of the applied amount (10 mg/g soil) remained in submerged soil but 82% was found in moist soil (Ko and Farley, 1969). In a Hagerstown silty clay loam, pentachloroaniline, pentachlorothioanisole, and pentachlorophenol were reported as metabolites (Murthy and Kaufman, 1978). [Pg.1603]

CASRN 51707-55-2 molecular formula C9H8N4OS FW 220.20 Soil. The reported half-life in soil is approximately 26-144 d (Hartley and Kidd, 1987). Photolytic. Klehr et al. (1983) studied the photolysis of thiadiazuron on adsorbed soil surfaces. Irradiation was conducted using artificial sunlight having a wavelength <290 nm. The amount of thiadiazuron remaining after irradiation times of 0.25, 0.5, 1, 2, 3.75, and 18.0 h were 56.4, 42.8, 35.7, 23.8, 25.0, and 67.2%, respectively. The primary photoproduct identified was l-phenyl-3-(l,2,5-thiadiazol-3-yl)urea and five unknown polar compounds. The unknown com pounds could not be identified because the quantities were too small to be detected. [Pg.1616]

ISOTOPES There are 45 isotopes of rhenium. Only one of these is stable Re-185, which contributes 37.40% to the total amount of rhenium found on Earth. Re-187, which is radioactive with a very long half-life of 4.35x10+ ° years, contributes 62.60% to rhenium s existence on Earth. The remaining 43 isotopes are radioactive with relatively short... [Pg.155]

Source. Uranium-238 is present in small amounts in most rocks and soil. Uranium has a half-life of 4.5 billion years. It decays to other elements such as radium, which breaks down to radon. Some of the radon moves to the soil surface and enters the air, whereas some remains below the soil surface and enters the groundwater. [Pg.615]


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