Nuclear reactions radioactive dating

Radiocarbon dating (43) has probably gained the widest general recognition (see Radioisotopes). Developed in the late 1940s, it depends on the formation of the radioactive isotope and its decay, with a half-life of 5730 yr. After forms in the upper stratosphere through nuclear reactions of... 

Radioactive, short-lived element. The longest-lived isotope (256Md) has a half-life of 55 days. To date, only a few atoms have been prepared by a nuclear reaction between einsteinium and helium nuclei in a particle accelerator. 

Radiocarbon Dating. This is a method of estimating Ihe age of carbon-containing materials by measuring the radioactivity of the carbon in them. The validity of this method rests upon certain observations and assumptions, of which the following statement is a brief summaiy. The cosmic rays entering the atmosphere undergo various transformations, one of which results in the formation of neutrons, which in turn, induce nuclear reactions in the nuclei of individual atoms of the adnosphere. The dominant reaction is... 

Chapter 13 is Chapter 4 from the previous edition and focuses on fundamental nuclear chemistry. Usefiil apphcations of radioactivity are considered. In this context, a discussion of the nse of radiocarbon dating has been added. A msgor focus of the chapter is the use of energy from nuclear reactions and this discussion has driven the chapter placement after the chapter on hydrocarbon fiiels. Comparisons between low-level radioactive waste and high-level radioactive waste have been added. 

The situation was clarified in 1965 when the Dubna group carried out the nuclear reaction Am( 0, 5re) 103 giving rise to the isotope with a mass number of 256 and determined its parameters. They coincided with those reported by the Berklev scientists for the product of the nuclear reaction Cf( B, 4k) 103 three years later. This is why the discovery date of 1961 can be doubted. But no definite conclusion was reached who and when had discovered element 103. As with element 102, researchers had to work with just a few atoms of element 103. At first, they found the mass numbers and the radioactive properties of the isotopes and only later the methods for evaluating their chemical nature were found. 

Nuclear chemistry affects our lives in a variety of ways. Radioactive elements are widely used in medicine as diagnostic tools and as a means of treatment, especially for cancer (Figure 21.1 ). They are also used to help determine the mechanisms of chemical reactions, to trace the movement of atoms in biological systems, and to date important historical artifacts. Nuclear reactions are used both to generate electricity and to create weapons of massive destruction. 

Radioactive nuclei emit a particles, 13 particles, positrons, or y rays. The equation for a nuclear reaction includes the particles emitted, and both the mass numbers and the atomic numbers must balance. Uranium-238 is the parent of a natural radioactive decay series. A number of radioactive isotopes, such as and C, can be used to date objects. Artificially radioactive elements are created by the bombardment of other elements by accelerated neutrons, protons, or a particles. Nuclear fission is the splitting of a large nucleus into smaller nuclei plus neutrons. When these neutrons are captured efficiently by other nuclei, an uncontrollable chain reaction can occur. Nuclear reactors use the heat... 

Most CO and CO2 in the atmosphere contain the mass 12 isotope of carbon. However, due to the reaction of cosmic ray neutrons with nitrogen in the upper atmosphere, C is produced. Nuclear bomb explosions also produce C. The C is oxidized, first to CO and then to C02 by OH- radicals. As a result, all CO2 in the atmosphere contains some 0, currently a fraction of ca. 10 of all CO2. Since C is radioactive (j -emitter, 0.156 MeV, half-life of 5770 years), all atmospheric CO2 is slightly radioactive. Again, since atmospheric CO2 is the carbon source for photos5mthesis, aU biomass contains C and its level of radioactivity can be used to date the age of the biological material. 

Radioactive heavy elements such as uranium, thorium, or plutonium are used as nuclear fuel radium is used in the radiography of metals and radon is used as a surface label to study surface reactions, as well, in the determination of radium or thorium. Among the lighter isotopes, Ni is used in electron capture detectors for GC analysis, in radiocarbon dating and as a tracer, and tritium in nuclear fusion and as a tracer in the studies of reactions. Many radioactive elements are used as a source of radiation, in medicine to diagnose disease, and for treatment. 

SECTIONS 21.4 AND 21.5 The SI unit for the activity of a radioactive source is the becquerel (Bq), defined as one nuclear disintegration per second. A related unit, the curie (Ci), corresponds to 3.7 X 10 disintegrations per second. Nuclear decay is a first-order process. The decay rate (activity) is therefore proportional to the number of radioactive nuclei. The half-life of a radionuclide, which is a constant, is the time needed for one-half of the nuclei to decay. Some radioisotopes can be used to date objects C, for example, is used to date organic objects. Geiger counters and scintillation counters count the emissions from radioactive samples. The ease of detection of radioisotopes also permits their use as radiolracers to follow elements through reactions. 

A second problem associated with nuclear power is waste disposal. Although the amormt of nuclear fuel used in electricity generation is small compared to other fuels, the products of the reaction are radioactive and have very long half-lives (thousands of years or more). What do we do with this waste Currently, in the United States, nuclear waste is stored on site at the nuclear power plants. A permanent disposal site was being developed in Yucca Mountain, Nevada. The site had originally been scheduled to be operational in 2010, and that date was later delayed to 2017. However, the Obama administration determined that the Yucca Mountain site was untenable, and in the spring of 2010, the license application to develop this... 

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