Radioactive decay rates

Radioactive decay rates 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. Each radioisotope has a different half-life. The decay of a radioisotope is described as follows. 

Radiochemical methods of analysis take advantage of the decay of radioactive isotopes. A direct measurement of the rate at which a radioactive isotope decays may be used to determine its concentration in a sample. For analytes that are not naturally radioactive, neutron activation often can be used to induce radioactivity. Isotope dilution, in which a radioactively labeled form of an analyte is spiked into the sample, can be used as an internal standard for quantitative work. 

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

Because exposure to radiation is a health risk, the administration of radioactive isotopes must be monitored and controlled carefully. Isotopes that emit alpha or beta particles are not used for Imaging, because these radiations cause substantial tissue damage. Specificity for a target organ is essential so that the amount of radioactive material can be kept as low as possible. In addition, an Isotope for medical Imaging must have a decay rate that is slow enough to allow time to make and administer the tracer compound, yet fast enough rid the body of radioactivity in as short a time as possible. 

The normal or constant radioactivity possessed by thorium is an equilibrium value, where the rate of increase of radioactivity due to the production offresh active material is balanced by the rate of decay of radioactivity of that already formed (Rutherford and Soddy 1902). 

It has been hoped [20,21] that a method could be developed which would directly detect the radioatoms that are present in nature by an efficient ultra-sensitive mass spectrometer technique which would not itself depend upon the fact that the atoms being investigated are radioactive. The advantage of an efficient mass spectrometer system for long-lived radioisotopes can be seen from the equation for calculating the number of atoms present in a sample from its measured radioactive decay rate ... 

The rate coefficient, kr, has units of t x and so can equally well be thought of in terms of the characteristic time for the reaction to take place. Hence if krt 1, the reaction will be a long way towards completion, whereas if krt 1, very little change will have occurred. Equation 1.10 describes the decay of radioactive elements and 1 jkT could be considered as the characteristic time for the relaxation of the element from its active to its non-active state. 

Disintegrations per minute (dpm) The unit measurement of radioactive decay rates. 

Apart from these three facts, nuclear astrophysicists take pains to point out that the rate at which the luminosities of SNla events decline, once beyond the maximum, is commensurable with the decay of radioactive cobalt-56, son of nickel-56, atomic nucleus of noble lineage as we know. This is a common factor with gravitational collapse supernovas. SNla light curves are explained through the hypothesis that half a solar mass of nickel-56 is produced when one of these white dwarfs explodes. 

Any geochronometric method for estimating the age of objects based upon the generation of radioactive isotopes by cosmic radiation, followed by isotopic incorporation into the biosphere/geosphere, and their subsequent first-order decay with release of radiation and/or accumulation of daughter isotopes. These methods take advantage of the lack of any dependence of the decay rate on temperature, pressure, pH, or other physical parameters. See Radiocarbon Dating... 

A 1. Symbol for Avogadro s number (rarely). 2. Symbol for wavelength. 3. Symbol for radioactive constant (decay rate constant). 4. Symbol for absolute chemical activity. 5. Symbol for thermal conductivity. 6. Symbol for mean free path. 

A specific example of applications in the second category is the dating of rocks. Age determination is an inverse problem of radioactive decay, which is a first-order reaction (described later). Because radioactive decay follows a specific law relating concentration and time, and the decay rate is independent of temperature and pressure, the extent of decay is a measure of time passed since the radioactive element is entrapped in a crystal, hence its age. In addition to the age, the initial conditions (such as initial isotopic ratios) may also be inferred, which is another example of inverse problems. 

The decay equation can also be expressed in terms of the radioactive activity (A), i.e., the number of decays per unit time per unit mass of sample. By definition, activity is the same as the decay rate, and can be written as... 

In Chapter 12, the concept of half-life was used in connection with the time it took for reactants to change into products during a chemical reaction. Radioactive decay follows first order kinetics (Chapter 12). First order kinetics means that the decay rate... 

J Ju elements in the periodic table exist in unstable versions called radioisotopes (see Chapter 3 for details). These radioisotopes decay into other (usually more stable) elements in a process called radioactive decay. Because the stability of these radioisotopes depends on the composition of their nuclei, radioactivity is considered a form of nuclear chemistry. Unsurprisingly, nuclear chemistry deals with nuclei and nuclear processes. Nuclear fusion, which fuels the sun, and nuclear fission, which fuels a nuclear bomb, are examples of nuclear chemistry because they deal with the joining or splitting of atomic nuclei. In this chapter, you find out about nuclear decay, rates of decay called half-lives, and the processes of fusion and fission. 

The word radioactive sounds scciry, but science and medicine are stuffed with useful, friendly applications for radioisotopes. Many of these applications are centered on the predictable decay rates of various radioisotopes. These predictable rates are characterized by half-lives. The half-life of a radioisotope is simply the amount of time it tcikes for exactly half of a sample of that isotope to decay into daughter nuclei. For excimple, if a scientist knows that a sample originally contained 42 mg of a certain radioisotope and measures 21 mg of that isotope in the sample four days later, then the half-life of that radioisotope is four days. The half-lives of radioisotopes range from seconds to billions of yecirs. 

The half-lives of 238U, 235U, and 232Th are all very much longer than those of the radioactive daughter isotopes in their decay chains. Therefore, a condition known as secular equilibrium is quickly established in which the decay rates of the daughter isotopes in the decay chain equal that of the parent isotope. In a closed system, once secular equilibrium is... 

Polybrominated Biphenyls. Rats given a single intravenous dose of " C-2,2, 4,4, 5,5 -hcxabromobiphenyl excreted a cumulative 0.96, 3.3, and 6.6% of the dose in the feces 1, 7, and 42 days after dosing, respectively (Matthews et al. 1977). Only traces (0.1% of the dose) were excreted in the urine. Two decay components were calculated from excretion data an initial decay rate of 1.05% of the dose/day and a later rate of 0.15% of the dose/day. Biliary excretion accounted for 0.68% of the dose between 0 and 4 hours after dosing. Analysis of bile and feces showed that at least 95% of the radioactivity corresponded to the parent compound. Moreover, in rats, 35% of the radioactivity excreted in the bile during the first week after a single dosing was reabsorbed (Tuey and Matthews 1980). 

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