Aging radiochemical

Esat TM, Yokoyama Y (1999) Rapid fluctuations in the uranium isotope composition of the oceans (abstract). Eos Transactions AGU 80(46(Fall meeting supl)) 581 Fomes WL, DeMaster DJ, Smith CR (2001) A particle introduction experiment in Santa Catalina Basin sediments Testing the age-dependent mixing hypothesis. J Marine Res 59(1) 97-112 Francois R, Bacon MP (1994) Heimich events in the North Atlantic radiochemical evidence. Deep-Sea Res 141 315-334... 

The Zag meteorite fell in the western Sahara of Morocco in August 1998. This meteorite was unusual in that it contained small crystals of halite (table salt), which experts believe formed by the evaporation of brine (salt water). It is one of the few indications that liquid water, which is essential for the development of life, may have existed in the early solar system. The halite crystals in the meteorite had a remarkably high abundance of 128Xe, a decay product of a short-lived iodine isotope that has long been absent from the solar system. Scientists believe that the iodine existed when the halite crystals formed. The xenon formed when this iodine decayed. For this reason, the Zag meteorite is believed to be one of the oldest artifacts in the solar system. In this lab, you will use potassium-argon radiochemical dating to estimate the age of the Zag meteorite and the solar system. 

Determine the age of the Zag meteorite, using potassium-argon (K-Ar) radiochemical dating. 

The problem of radiochemical purity with respect to the chemical state of aged tritium or 14C-labeled compounds is still more acute. Because of the short range... 

Aging can be defined as a slow and irreversible (in use conditions) variation of a material s structure, morphology and/or composition, leading to a deleterious change of use properties. The cause of this change can be the proper material s instability in use conditions or its interaction with the environment (oxidation, hydrolysis, photochemical, radiochemical, or biochemical reactions, etc.). 

Photochemical or radiochemical aging are not examined here for many reasons ... 

Radiochemical aging has very specific applications. The uses of thermosets in nuclear engineering have been growing. Most of the data on radiochemical aging of thermosets, available at the beginning of the 1990s, has been reviewed (Wilski, 1991). 

Q Radiochemical dating is often used to determine the age of bones discovered at archaeological sites. Using this technique, these human bones frozen in a glacier were estimated to be from about 3000 B.c. 

A type of radiochemical dating known as carbon dating is commonly used to measure the age of artifacts that were once part of a living organism, such as the human skeleton shown in Figure 25-14. Carbon dating, as its name implies, makes use of the radioactive decay of carbon-14. The procedure rehes on the fact that unstable carbon-14 is formed by cosmic rays in the upper atmosphere at a fairly constant rate. 

The decay process of a different radioisotope, uranium-238 to lead-206, is commonly used to date objects such as rocks. Because the half-life of uranium-238 is 4.5 X 10 years, it can be used to estimate the age of objects that are too old to be dated using carbon-14. By radiochemical dating of meteorites, the age of the solar system has been estimated at 4.6 X 10 years of age. 

Radiochemical dating is a technique for determining the age of an object by measuring the amount of certain radioisotopes remaining in the object. 

For some samples of more recent origin there is good historical or archaeological evidence for the age, and this provides a check on the radiochemical method. For example, the Egyptian king Ptolemy V, who married Cleopatra, is known to have lived from about 203 to 181 B.C., or about 2150 years ago. Articles fabricated at that time would therefore be expected to have a radioactivity of about... 

Estimates of the age of our galaxy comes mainly from theoretical calculations. However, radiochemical investigations can yield information about several important steps. Thus the time since the final solidification of the earth s crust is obtained from the dating of geologic... 

Recently there has come new radiochemical evidence about the age of our Galaxy. Consider Figure 17.9, which shows a part of a nuclide chart the zigzag arrow shows nuclides formed in the s-process, the lower right arrows nuclides formed by the r-process. 

Craciun, E., Jitaru, I., Zaharescu, T., Jipa, S. Qualification of qroxy resin by radiochemical ageing. Optoelectr. Adv. Mater. Rapid Commun. 4, 1819-1822 (2010)... 

The dynamic range in the measurement of nuclide concentrations required by chronometry makes it impossible to perform accurate age assessments without radiochemical separations. However, when the nuclide to be determined is present as a minor component in an overwhelming concentration of isotopes of the same element, chemical separations are of limited use. In these instances, the method of radiochemical milking has proven to be valuable. 

In the case of radiochemical ageing (high energy provided), the main source of radicals is the polymer radiolysis, i.e. the breakdown of lateral bonds of the monomer unit. As an example, in the ease of PE, radiolysis leads to the formation of very reaetive radieals H whieh recombine rapidly by hydrogen... 

Shape of oxidation kinetic curves in the case of initiation (a) at constant rate (case of radiochemical ageing) thermal ageing) and (c) by unimolecular Per decomposition (case of many photochemical ageings). 

The modification of antioxidant mobility by radiochemical grafting ameliorates the oxidation strength, which lengthens the duration of material suppressing the initiation of degradation under the accelerated ageing conditions for special applications. 

Emmanuel Richaud, Paulo Ferreira, Ludmila Audouin, Xavier Colin, Jacques Verdu, and Carole Monchy-Leroy. "Radiochemical ageing of polyCether ether ketone)." European Polymer Journal, pp. 731-743, 2010. 

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