# What is radioactive dating and half life

Half-life , in radioactivity , the interval of time required for one-half of the atomic nuclei of a radioactive sample to decay change spontaneously into other nuclear species by emitting particles and energy , or, equivalently, the time interval required for the number of disintegrations per second of a radioactive material to decrease by one-half. The radioactive isotope cobalt, which is used for radiotherapy , has, for example, a half-life of 5. Thus after that interval, a sample originally containing 8 g of cobalt would contain only 4 g of cobalt and would emit only half as much radiation. After another interval of 5. Neither the volume nor the mass of the original sample visibly decreases, however, because the unstable cobalt nuclei decay into stable nickel nuclei, which remain with the still-undecayed cobalt. Half-lives are characteristic properties of the various unstable atomic nuclei and the particular way in which they decay.

## 5.7: Calculating Half-Life

The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo, or how long stable atoms survive, radioactive decay. The term is also used more generally to characterize any type of exponential or non-exponential decay. For example, the medical sciences refer to the biological half-life of drugs and other chemicals in the human body. The converse of half-life is doubling time.

The original term, half-life period , dating to Ernest Rutherford 's discovery of the principle in , was shortened to half-life in the early s. Half-life is constant over the lifetime of an exponentially decaying quantity, and it is a characteristic unit for the exponential decay equation. The accompanying table shows the reduction of a quantity as a function of the number of half-lives elapsed. A half-life usually describes the decay of discrete entities, such as radioactive atoms.

In that case, it does not work to use the definition that states "half-life is the time required for exactly half of the entities to decay". For example, if there is just one radioactive atom, and its half-life is one second, there will not be "half of an atom" left after one second. Instead, the half-life is defined in terms of probability: For example, the image on the right is a simulation of many identical atoms undergoing radioactive decay. Note that after one half-life there are not exactly one-half of the atoms remaining, only approximately , because of the random variation in the process.

Nevertheless, when there are many identical atoms decaying right boxes , the law of large numbers suggests that it is a very good approximation to say that half of the atoms remain after one half-life. There are various simple exercises that demonstrate probabilistic decay, for example involving flipping coins or running a statistical computer program. Some quantities decay by two exponential-decay processes simultaneously. The term "half-life" is almost exclusively used for decay processes that are exponential such as radioactive decay or the other examples above , or approximately exponential such as biological half-life discussed below.

In a decay process that is not even close to exponential, the half-life will change dramatically while the decay is happening. In this situation it is generally uncommon to talk about half-life in the first place, but sometimes people will describe the decay in terms of its "first half-life", "second half-life", etc. A biological half-life or elimination half-life is the time it takes for a substance drug, radioactive nuclide, or other to lose one-half of its pharmacologic, physiologic, or radiological activity.

In a medical context, the half-life may also describe the time that it takes for the concentration of a substance in blood plasma to reach one-half of its steady-state value the "plasma half-life". The relationship between the biological and plasma half-lives of a substance can be complex, due to factors including accumulation in tissues , active metabolites , and receptor interactions. While a radioactive isotope decays almost perfectly according to so-called "first order kinetics" where the rate constant is a fixed number, the elimination of a substance from a living organism usually follows more complex chemical kinetics.

For example, the biological half-life of water in a human being is about 9 to 10 days, [7] though this can be altered by behavior and various other conditions. The biological half-life of caesium in human beings is between one and four months. The concept of a half-life has also been utilized for pesticides in plants , [8] and certain authors maintain that pesticide risk and impact assessment models rely on and are sensitive to information describing dissipation from plants.

From Wikipedia, the free encyclopedia. This article is about the scientific and mathematical concept. For the video game, see Half-Life video game. For other uses, see Half-Life disambiguation. Main article: Exponential decay. Further information: See also: Biological half-life. What happens durring half lifes [sic] when there is only one atom left? Retrieved Data, Simulations, and Analytic Science in Decay". Archived from the original on CS1 maint: Chemistry for the Biosciences: The Essential Concepts.

Spinal cord medicine. Molecular Structure and Properties. New Jersey: World Scientific. Australian Government. Retrieved 30 April Radiation physics and health. Earth's energy budget Electromagnetic radiation Synchrotron radiation Thermal radiation Black-body radiation Particle radiation Gravitational Radiation Cosmic background radiation Cherenkov radiation Askaryan radiation Bremsstrahlung Unruh radiation Dark radiation. Radiation syndrome acute chronic Health physics Dosimetry Electromagnetic radiation and health Laser safety Lasers and aviation safety Medical radiography Mobile phone radiation and health Radiation protection Radiation therapy Radioactivity in the life sciences Radioactive contamination Radiobiology Biological dose units and quantities Wireless electronic devices and health Radiation Heat-transfer.

Authority control GND: Retrieved from " https: Radioactivity Exponentials Chemical kinetics. Hidden categories: Namespaces Article Talk. Views Read Edit View history. In other projects Wikimedia Commons. This page was last edited on 25 April , at By using this site, you agree to the Terms of Use and Privacy Policy. Look up half-life in Wiktionary, the free dictionary. Wikimedia Commons has media related to Half times.

## The term "half-life" is almost exclusively used for decay processes that are exponential (such as radioactive decay or. RADIOACTIVE HALF-LIFE (CONTINUED). After this reading this section you will be able to do the following: Describe carbon dating and how half-life.

Generally, there are four main concepts that students struggle with when thinking about radioactive decay:. Radioactivity and radioactive decay are spontaneous processes. Students often struggle with this concept; therefore, it should be stressed that it is impossible to know exactly when each of the radioactive elements in a rock will decay. Statistical probablity is the only thing we can know exactly. Often students get bogged down in the fact that they don't "understand" how and why radioactive elements decay and miss the whole point of this exercise.

Geologists use radiometric dating to estimate how long ago rocks formed, and to infer the ages of fossils contained within those rocks.

Geologist Ralph Harvey and historian Mott Greene explain the principles of radiometric dating and its application in determining the age of Earth. As the uranium in rocks decays, it emits subatomic particles and turns into lead at a constant rate.

## 10.3: Half-life & Rate of Radioactive Decay

During natural radioactive decay, not all atoms of an element are instantaneously changed to atoms of another element. The decay process takes time and there is value in being able to express the rate at which a process occurs. Half-lives can be calculated from measurements on the change in mass of a nuclide and the time it takes to occur. The only thing we know is that in the time of that substance's half-life, half of the original nuclei will disintegrate. Although chemical changes were sped up or slowed down by changing factors such as temperature, concentration, etc, these factors have no effect on half-life. Each radioactive isotope will have its own unique half-life that is independent of any of these factors.

## Radioactive Decay

Radiometric dating is a means of determining the "age" of a mineral specimen by determining the relative amounts present of certain radioactive elements. By "age" we mean the elapsed time from when the mineral specimen was formed. Radioactive elements "decay" that is, change into other elements by "half lives. The formula for the fraction remaining is one-half raised to the power given by the number of years divided by the half-life in other words raised to a power equal to the number of half-lives. If we knew the fraction of a radioactive element still remaining in a mineral, it would be a simple matter to calculate its age by the formula. To determine the fraction still remaining, we must know both the amount now present and also the amount present when the mineral was formed. Contrary to creationist claims, it is possible to make that determination, as the following will explain:. By way of background, all atoms of a given element have the same number of protons in the nucleus; however, the number of neutrons in the nucleus can vary. An atom with the same number of protons in the nucleus but a different number of neutrons is called an isotope. For example, uranium is an isotope of uranium, because it has 3 more neutrons in the nucleus.

After this reading this section you will be able to do the following:

Radiometric dating, often called radioactive dating, is a technique used to determine the age of materials such as rocks. It is based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates. It is the principal source of information about the absolute age of rocks and other geological features, including the age of the Earth itself, and it can be used to date a wide range of natural and man-made materials. The best-known radiometric dating techniques include radiocarbon dating, potassium-argon dating, and uranium-lead dating.

## Half-life and carbon dating

A process for determining the age of an object by measuring the amount of a given radioactive material it contains. If one knows how much of this radioactive material was present initially in the object by determining how much of the material has decayed , and one knows the half-life of the material, one can deduce the age of the object. The simple days of immediately understanding what SWF means are far behind us. Online dating has made acronyms more inscrutable—and more fun—than ever. Take our quiz and find out. We hope this made it a little bit easier to navigate those stormy dating waters. So why is it so special? First recorded in — Also called radioactive dating. A method for determining the age of an object based on the concentration of a particular radioactive isotope contained within it. For inorganic materials, such as rocks containing the radioactive isotope rubidium, the amount of the isotope in the object is compared to the amount of the isotope's decay products in this case strontium.

## Radiometric Dating: Methods, Uses & the Significance of Half-Life

Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4. Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free. These changes typically occur so slowly that they are barely detectable over the span of a human life, yet even at this instant, the Earth's surface is moving and changing. As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils. A fossil can be studied to determine what kind of organism it represents, how the organism lived, and how it was preserved.

## Dating Rocks and Fossils Using Geologic Methods

Radiometric dating , radioactive dating or radioisotope dating is a technique used to date materials such as rocks or carbon , in which trace radioactive impurities were selectively incorporated when they were formed. The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay. Together with stratigraphic principles , radiometric dating methods are used in geochronology to establish the geologic time scale. By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change. Radiometric dating is also used to date archaeological materials, including ancient artifacts.

## radiometric dating

Radioactive dating is a method of dating rocks and minerals using radioactive isotopes. This method is useful for igneous and metamorphic rocks, which cannot be dated by the stratigraphic correlation method used for sedimentary rocks. Over naturally-occurring isotopes are known. Some do not change with time and form stable isotopes i. The unstable or more commonly known radioactive isotopes break down by radioactive decay into other isotopes. Radioactive decay is a natural process and comes from the atomic nucleus becoming unstable and releasing bits and pieces.

## Radiometric dating

If you're seeing this message, it means we're having trouble loading external resources on our website. To log in and use all the features of Khan Academy, please enable JavaScript in your browser. Science Chemistry Nuclear chemistry Radioactive decay. Mass defect and binding energy. Nuclear stability and nuclear equations. Types of decay. Writing nuclear equations for alpha, beta, and gamma decay.

## Radioactive dating

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Radioactive Dating