Potassium , decay

The radioactive, naturally occurring isotope of potassium——decays by emission... 

Branching decay is often observed for odd-odd nuclei on the line of P stability. For example, °K, which is responsible for the natural radioactivity of potassium, decays into Ca with a probability of 89.3% by emission of particles and into Ar with a probability of 10.7% by electron capture. Branching decay is also observed in the decay series, as already mentioned in section 4.1. 

Radioactive elements in rocks (see Section 2.8), most importantly potassium (K) and heavy elements such as radium (Ra), uranium (U) and thorium (Th), can release gases. Argon (Ar) arises from potassium decay and radon (Rn, a radioactive gas that has a half-life of 3.8 days) from radium decay. The uranium-thorium decay series results in the production of a particles, which are helium nuclei. Once these nuclei capture electrons, helium has effectively been added to the atmosphere. 

The radioactive potassium-40 isotope decays to aigon-40 with a half-life of 1.2 X 10 years, (a) Write a balanced equation fior the reaction, (b) A sample of moon rock is found to contain 18 percent potassium-40 and 82 percent argon by mass. Calculate the age of the rock in years. (Assume that all the argon in the sample is the result of potassium decay.)... 

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

The element potassium occurs naturally as " K, and "K. Of these, the is most abundant and " K is radioactive. The decay of " K follows two paths, one giving Ar and the other "Ca, as shown below. 

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,... 

Argon-40 [7440-37-1] is created by the decay of potassium-40. The various isotopes of radon, all having short half-Hves, are formed by the radioactive decay of radium, actinium, and thorium. Krypton and xenon are products of uranium and plutonium fission, and appreciable quantities of both are evolved during the reprocessing of spent fuel elements from nuclear reactors (qv) (see Radioactive tracers). 

Potassium nitrate is also found in pills for backache and joint pain. It makes a decent plant fertilizer, providing nitrogen and potassium but no phosphorus. As an oxidizer, it is an ingredient in stump removers that hastens the decay of tree stumps. And it is used as a preservative in some salted meats like nitrites, it helps to preserve the color of the meat. 

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. 

In a different example, traceability in the amount-of-substance analysis of natural potassium, thorium, and uranium by the method of passive gamma-ray spectrometry was demonstrated by Nir-El (1997). For an absolute quantitative determination, accurate values of two parameters were required (i) the emission probability of a gamma-ray in the decay of the respective indicator radionuclides, and (2) the detection efficiency of that gamma-ray. This work employed a number of CRMs in the critical calibration of the detection efficiency of the gamma-ray spectrometer and the establishment of precise emission probabilities. The latter results compared well with literature values and provided smaller uncertainties for several gamma-rays that were critical for the traceabUity claim. The amount-of-substance analytical results of the long lived naturally occurring radionucHdes K, Th, and... 

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. 

Chemical analyses can measure the total quantities of N, P and K in FYM but not their availability to the crop. At most, all of the N in FYM is combined with organic substances and is released only when they decay in practice about a third of the nitrogen is released quite quickly, but much is very resistant and persists in the soil. Much of the phosphorus is also combined with the organic matter but approximately half is quickly available. Most of the potassium is soluble in water and is quickly available to the crop. 

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). 

T1, as the thallous ion (Tl+), has been used for imaging heart function under stress and rest conditions since about 1975. The thallous ion distributes in viable heart muscle as a potassium ion mimic, through the Na+-K+ ATPase pump. Clinical images with 201T1 show the infarcted regions of the heart as cold spots or without radioactivity. 2 T1 decays by electron capture with a... 

Figure 4 shows the behavior that is observed when a solution of cationic radon in 1,1,2-trichlorotrifluoroethane is passed through a column packed with KPF. The radon displaces potassium ion and adheres in a narrow band at the top of the column. It can be washed repeatedly with dilute BrF in the halocarbon solvent, then eluted rapidly with 1.0 M BrF in sulfuryl chloride. The radon daughters remain on the column during elution and decay in situ new daughters are generated in the radon-containing eluant fractions. 

This very long half-life (1.25x1(r years) isotope comprises 0.0117 percent of all potassium. Thus, this isotope is present in all of us and has always been so. In addition, the materials around us, including the soil and the building materials, contain both potassium and the heavy naturally occurring radioactive elements thorium and uranium that contribute to a level of radiation to which we are all continuously exposed. Thus, there is always radiation exposure to the general public and we must understand the exposure due to radon in this context. The amount of radioactivity is described in units of activity. The activity is the number of decay events per unit time and is calculated as follows... 

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