Half-life of potassium

Data on the percentage bioavailability, volume of distribution, and half-life of potassium iodide are not... 

A rock was analyzed using potassium-40. The half-life of potassium-40 is 1.25 biUion years. If the rock had only 25 percent of the potassium-40 that would be foimd in a similar rock formed today, calculate how long ago the rock was formed. 

In cattle, the potassium content of the muscles decreases with increasing age (Sim and Wellington 1976). The biological half-life of potassium is 10.5 days in cows and 45.6 days in obese pigs (Robinson etal. 1961). 

This method is limited to objects less than about 50,000 years old because of difficulties in measuring the small amount of carbon-14 present. For this reason, other dating methods have been developed. One method involves potassium-40 and argon-40. The half-life of potassium-40, which absorbs one of its own inner electrons to produce argon-40, is 1.3 X 10 years. By determining the amount of argon-40 in a potassium-containing mineral, it is possible to estimate the age of the mineral. The equation for the reaction is... 

The half-life of potassium-40 is 1.3 x 10 years. A volcanic rock contains of the amount of potassium-40 found in newiy formed rocks. When was the rock formed ... 

The half-life of potassium-40 is 1.28 billion years, which is about one-third the age of Earth. With such a long half-life, the amount of potassium-40 still remaining in Earth s crust is... 

The results of these analyses showed that the sample contained 3.02 X 10 mLg at STP of argon and 0.083% of potassium. The half-life of potassium-40 is 1.26 X 10 years. Calculate the age of the lunar rock. 

What is the age of a piece of volcanic rock that has a mass ratio of argon-40 to potassium-40 of 1.9 The half-life of potassium-40 by /3 decay is 1.26 X 10 years and by electron capture, 1.4 X 10 years. 

Seventeen isotopes of potassium are known. Ordinary potassium is composed of three isotopes, one of which is 40oK (0.0118%), a radioactive isotope with a half-life of 1.28 x IO9 years. 

Thirty isotopes are recognized. Only one stable isotope, 1271 is found in nature. The artificial radioisotope 1311, with a half-life of 8 days, has been used in treating the thyroid gland. The most common compounds are the iodides of sodium and potassium (KI) and the iodates (KIOs). Lack of iodine is the cause of goiter. 

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. 

The sodium and potassium salts are veiy soluble in water but they are hydrolysed in solution, at a temperature-dependent rate, to the corresponding penicilloic acid (Fig. 5.3 A see also Fig. 9.3), which is not antibacterial. Penicilloic acid is produced at alkaline pH or (via penieillenic acid Fig. 5.3B) at neutral pH, but at acid pH a molecular rearrangement oeeurs, giving penillic acid (Fig. 5.3C). Instability in acid medium logically precludes oral administration, since the antibiotic may be destroyed in the stomach for example at pH 1.3 and 35°C methicillin has a half-life of only 2-3 minutes and is therefore not administered orally, whereas ampicillin, with a half-life of 600 minutes, is obviously suitable for oral use. 

Photolytic. The photodegradation rate of amitrole in water increased in the presence of humic acid. Under simulated sunlight, the half-life of amitrole in water containing 100 mg/L of humic acid-potassium salt was 7.5 h. Degradation did not occur in the absence of humic acid (Jensen-Korte et al, 1987). Direct photolysis of amitrole is not expected to occur because the herbicide shows little or no absorption at wavelength greater than 295 nm (Gore et al., 1971). 

ISOTOPES A total of 18 isotopes of potassium have been discovered so far. Just two of them are stable K-39 makes up 93.2581% of potassium found in the Earth s crust, and K-41 makes up 6.7301% of the remainder of potassium found on Earth. All the other 16 potassium isotopes are unstable and radioactive with relatively short half-lives, and as they decay, they produce beta particles. The exception is K-40, which has a half-life of 1.25x10 years. 

A particular hazard, which has been with humans since the beginning of time, is the radioactive isotope potassium-40 (K-40). Less than 1% of all potassium atoms on Earth are in the form of this radioactive isotope. It has a half-life of 1.25 billion years. Its decay process... 

A lunar expedition brought back some moon rocks. Analysis of the rocks showed them to contain 17% potassium-40 and 83% argon by mass. The half-life of K-40 is 1.2 x 10 years. K-40 decays through positron emission. Ar-40 is the decay product of the reaction. How old was the rock sample (in years) ... 

Spironolactone is poorly absorbed after oral administration and has a delayed onset of action it may take several days until a peak effect is produced. It has a somewhat slower onset of action than triamterene and amiloride (discussed later), but its natriuretic effect is modestly more pronounced, especially during long-term therapy. Spironolactone is rapidly and extensively metabolized, largely to the active metabohte canrenone. Canrenone and potassium canrenoate, its K+ salt, are available for clinical use in some countries outside the United States. Canrenone has a half-life of approximately 10 to 35 hours. The metabolites of spironolactone are excreted in both the urine and feces. New selective aldosterone receptor antagonists (SARA), such as eplerenone, have been developed but have not yet been introduced into clinical practice. Eplerenone and canrenone exhibit fewer steroidlike side effects (gynecomastia, hirsutism). 

Calcium-41 decays to 4XK with a half-life of 1.03 x 105 yr (A, = 6.73 x 10-6yr-1). Calcium is a refractory alkaline earth element, while potassium is a moderately volatile alkaline element. Thus, calcium and potassium can be separated by both chemical and thermal processes. The short half-life of 41Ca means that the abundance in the early solar system was very low. Therefore, minerals with very high Ca/K ratios are required in order for the... 

Potassium has three naturally occurring isotopes 39K (93.08%), 40K (0.01%), and 41K (6.91%). The radioactive decay of 4,)K to argon (40Ar), half-life of 109 years, makes it a useful tool for geological dating. Some physical properties of potassium are summarized in Table 1 (1—3). 

There are three naturally occurring isotopes, 39K through 41K, of which 40K is radioactive with a half-life of 1.3 109 years. Tn ordinary potassium, this isotope represents only 0.0119% of the content. There are four other known isotopes, all radioactive. 33 K and 42K through 44K, all with relatively short half-lives measured in minutes and hours. In terms of abundance, potassium ranks seventh among the elements occurring in the earth s crust. In terms of content in seawater, the element ranks eighth, with an estimated 1,800,000 tons of potassium per cubic mile (388,000 metric tons per cubic kilometer) of seawater, First ionization potential 4,339 eV ... 

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