Potassium 40 dating

Potassium-40 dating techniques can be tricky because of the properties of the decay product argon. What about argon makes it hard to measure ... 

One might wonder why argon gas does not escape into the atmosphere. The answer is that the argon gas is trapped within the solid rock. It is released only when the potassium-dating process is conducted. 

As the continues to decay with a half-life of 5,568 years, the isotopic ratio changes accordingly, and can thus be used to monitor the date of origin of the sample in question. The method is valid for determining with an error of only about 30 years the age of an object younger than 50,000 years. Other methods, such as thorium- and potassium-dating, are available for dating much older samples. 

Potassium-argon dating is based on the nuclear decay of... 

By using K/Ar isotope ratios, potassium-containing rocks can be dated to their first formation, even through millions of years. 

From the radioactive decay constants and measurement of the amount of argon in a rock sample, the length of time since formation of the rock can be estimated. Essentially, the dating method requires fusion of a rock sample under high vacuum to release the argon gas that has collected through radioactive decay of potassium. The amount of argon is determined mass spectrometrically,... 

Properties. Most of the alloys developed to date were intended for service as fuel cladding and other stmctural components in hquid-metal-cooled fast-breeder reactors. AHoy selection was based primarily on the following criteria corrosion resistance in Hquid metals, including lithium, sodium, and NaK, and a mixture of sodium and potassium strength ductihty, including fabricabihty and neutron considerations, including low absorption of fast neutrons as well as irradiation embrittlement and dimensional-variation effects. Alloys of greatest interest include V 80, Cr 15, Ti 5... 

Although the polysulfur macrocycles became more interesting to the scientific community after Pedersen s report of the crown compounds (see Chap. 1), examples of such structures may be found in the literature dating back some time. The first report of a macrocyclic polysulfide appears to be that by Ray who found in 1920 that when 1,2-dimercaptoethane and 1,2-dibromoethane were heated with alcoholic potassium hydrogen sulfide as shown in Eq. (6.2), triethylene trisulfide (2) and a substance presumed to be triethylene tetrasulfide (3) could be isolated. 

It is estimated that the earth s age is in the neighborhood of 4 to 7 billion years. These estimates are basically derived from carbon-14, potassium-40, uranium-235, and uranium-238 dating of earth rocks and meteorites. The meteorites give important data as to the age of our solar system. Geologic time is felt to be represented by the presence of rock intervals in the geologic column (layers of rock formations in vertical depth) or by the absence of equivalent rocks in correlative columns in adjacent locations [25,26]. The two basic factors that are used to determine geologic time are ... 

The proposed model for the so-called sodium-potassium pump should be regarded as a first tentative attempt to stimulate the well-informed specialists in that field to investigate the details, i.e., the exact form of the sodium and potassium current-voltage curves at the inner and outer membrane surfaces to demonstrate the excitability (e.g. N, S or Z shaped) connected with changes in the conductance and ion fluxes with this model. To date, the latter is explained by the theory of Hodgkin and Huxley U1) which does not take into account the possibility of solid-state conduction and the fact that a fraction of Na+ in nerves is complexed as indicated by NMR-studies 124). As shown by Iljuschenko and Mirkin 106), the stationary-state approach also considers electron transfer reactions at semiconductors like those of ionselective membranes. It is hoped that this article may facilitate the translation of concepts from the domain of electrodes in corrosion research to membrane research. 

The constant half-life of a nuclide is used to determine the ages of archaeological artifacts. In isotopic dating, we measure the activity of the radioactive isotopes that they contain. Isotopes used for dating objects include uranium-238, potassium-40, and tritium. However, the most important example is radiocarbon dating, which uses the decay of carbon-14, for which the half-life is 5730 a. 

Isotopes are also used to determine properties of the environment. Just as carbon-14 is used to date organic materials, geologists can determine the age of very old substances such as rocks by measuring the abundance in rocks of radioisotopes with longer half-lives. Uranium-238 (t1/2 = 4.5 Ga, 1 Ga = 10y years) and potassium-40 (t,/2 = 1.26 Ga) are used to date very old rocks. For example, potassium-40 decays by electron capture to form argon-40. The rock is placed under vacuum and crushed, and a mass spectrometer is used to measure the amount of argon gas that escapes. This technique was used to determine the age of rocks collected on the surface of the Moon they were found to be 3.5-4.0 billion years old, about the same age as the Earth. 

Ruxton, B. P. and McDougall, I. (1967) Denudation rates in northeast Papua from potassium-argon dating of lavas. Am. ]. Sci. 265,545-561. 

If the amount of a radioactive nuclide in a rock sample is N, the sum of this amount plus the amount of its product nuclide is A/q. For argon dating, Nq is the sum of potassium-40 and argon-40 present in a sample of rock. Assuming that Ar gas escapes from molten rock but is trapped when the rock cools and solidifies, the lifetime obtained by substituting these values into Equation is the time since the rock solidified. Such analyses show that the oldest rock samples on Earth are 3.8 X 10 years old. 

The logic underlying carbon-14 dating differs from that for potassium-argon dating. Recall that bombardment of... 

The Juan Fernandez Islands, Chile, he east of the South American mainland at approximately 33°30 S, 80°W (Fig. 6.8). The archipelago consists of two main islands, Masatierra, which lies about 660 km from the mainland, and Masafuera, which lies 150km further west. A third, small island, Santa Clara, lies off the western end of Masatierra and probably was attached to Masatierra at one time. The ages of the islands have been determined using potassium-argon dating methods to be 5.8 2.1 million years for Santa Clara 4.23 0.16 million years for Masatierra and 2.44 0.14 million years for Masafuera (Stuessy et ah, 1984). 

Stuessy, T. F., Foland, K. A., Sutter, J. F., Sanders, R. W. and Silva, O. M. 1984. Botanical and geological significance of potassium-argon dates from the Juan Fernandez Islands. Science 225 49-51. 

Effluents from conventional oxidations with classical stoichiometric inorganic oxidants, such as potassium dichromate and potassium permanganate, are very difficult to process and represent out-of-date chemistry. Replacement of conventional oxidations with catalytic oxidation using inexpensive and environmentally acceptable air as the oxidant is crucial. The same applies to hydrogenations using hydrides or the Wolf-Kizhner method with hydrazine. These methods of hydrogenation involve amounts of deleterious effluents and should be avoided. 

Date et al. (1983) found the existence of an Na20-depleted dacite mass with a lateral dimension of 1.5 x 3.0 km immediately below the ore horizon (Figs. 1.23 and 1.24) and the mass is useful indicator of exploration of Kuroko ore deposits. This Na20 depletion is considered to be due to the destruction of plagioclase attacked by potassium-... 

Curtis GH, Hay RL (1972) Further geological studies and potassium-argon dating at Oludvai Gorge and Ngorongoro Crater. In Calibration of Hominid Evolution. Bishop WW, Miller JA (eds), Scottish Academic Press, Edinburgh... 

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 most interesting aminomethyl derivative of condensation polymers that we have prepared to date Is derived from direct reduction of poly(2-cyano-l,3-phenylene arylene ether), 20. Enchainment of benzonitrile repeat units Is accomplished by coupling 2,6-dichlorobenzonitrile with the potassium salt of bisphenol-A copolymers with lower nitrile contents can be produced by copolycondensation of bisphenol-A, 2,6-dichlorobenzonitrile and 4,4 -dichlorodiphenyl sulfone.21 The pendent nitrile function provides an active site for further elaboration. 

This paper discusses the various names that were given to potassium nitrate in Arabic, and the equivalent words that were used in Latin. In investigating this subject the following question was posed what were the names of potassium nitrate in Arabic before the word barud became common Because the term barud was applied in Arabic to potassium nitrate in the thirteenth century, some historians of science and technology assumed that familiarity with potassium nitrate in Arabic chemistry and alchemy dates from the thirteenth century only"... 

Radioisotopes may occur in the earth naturally as primordial radioisotopes, formed when the planet was created, or be produced by natural or artificial processes. Most fast decaying primordial radioisotopes have long disappeared from the planet since the earth originated about 4.5 billion years ago, such isotopes have decayed and reached a final, stable form. The relatively few primordial radioisotopes still extant in the earth today, therefore, decay very slowly. Among these are potassium-40 and some isotopes of uranium, such as uranium-235 and uranium-238, which are of use for dating archaeologically related minerals and rocks (see Textboxes 15 and 16). 

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