decay

Examples of decay in the following topics:

• Radioactive Decay Series: Introduction

  • Radioactive decay series describe the decay of different discrete radioactive decay products as a chained series of transformations.
  • Radioactive decay series, or decay chains, describe the radioactive decay of different discrete radioactive decay products as a chained series of transformations.
  • Most radioactive elements do not decay directly to a stable state; rather, they undergo a series of decays until eventually a stable isotope is reached.
  • A parent isotope is one that undergoes decay to form a daughter isotope.
  • While the decay of a single atom occurs spontaneously, the decay of an initial population of identical atoms over time, $t$, follows a decaying exponential distribution, $e^{-t}$, where $\lambda$ is called the decay constant.

• Beta Decay

  • Beta decay is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted from an atomic nucleus.
  • There are two types of beta decay.
  • Beta decay is mediated by the weak force.
  • A beta-stable nucleus may undergo other kinds of radioactive decay (for example, alpha decay).
  • The inset shows beta decay of a free neutron

• Gamma Decay

  • Gamma decay is a process of emission of gamma rays that accompanies other forms of radioactive decay, such as alpha and beta decay.
  • Gamma decay accompanies other forms of decay, such as alpha and beta decay; gamma rays are produced after the other types of decay occur.
  • For example, cobalt-60 decays to excited nickel-60 by beta decay through emission of an electron of 0.31 MeV.
  • Path of decay of Co-60 to Ni-60.
  • Explain relationship between gamma decay and other forms of nuclear decay.

• Alpha Decay

  • Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle that consists of two protons and two neutrons, as shown in .
  • Alpha decay is the most common cluster decay because of the combined extremely high binding energy and relatively small mass of the helium-4 product nucleus (the alpha particle).
  • Alpha decay typically occurs in the heaviest nuclides.
  • Alpha decay is one type of radioactive decay.
  • Many other types of decay are possible.

• Nuclear Stability

  • Most odd-odd nuclei are highly unstable with respect to beta decay because the decay products are even-even and therefore more strongly bound, due to nuclear pairing effects.
  • During this process, the radionuclide is said to undergo radioactive decay.
  • Radioactive decay results in the emission of gamma rays and/or subatomic particles such as alpha or beta particles, as shown in .
  • Alpha decay is one type of radioactive decay.
  • Many other types of decay are possible.

• Calculations Involving Half-Life and Decay-Rates

  • The half-life of a radionuclide is the time taken for half the radionuclide's atoms to decay.
  • The half-life of a radionuclide is the time taken for half of the radionuclide's atoms to decay.
  • Taking $\lambda$ to be the decay rate (number of disintegrations per unit time) , and $\tau$ the average lifetime of an atom before it decays, we have:
  • A half-life must not be thought of as the time required for exactly half of the atoms to decay.
  • The following figure shows a simulation of many identical atoms undergoing radioactive decay.

• Conservation of Nucleon Number and Other Laws

  • Through radioactive decay, nuclear fusion and nuclear fission, the number of nucleons (sum of protons and neutrons) is always held constant.
  • Consider the three modes of decay.
  • In gamma decay, an excited nucleus releases gamma rays, but its proton (Z) and neutron (A-Z) count remain the same:
  • In beta decay, a nucleus releases energy and either an electron or a positron.
  • Alpha decay is the only type of radioactive decay that results in an appreciable change in an atom's atomic mass.

• Gamma Rays

  • Gamma rays are very high frequency electromagnetic waves usually emitted from radioactive decay with frequencies greater than 1019 Hz.
  • Gamma rays from radioactive decay are defined as gamma rays no matter what their energy, so that there is no lower limit to gamma energy derived from radioactive decay.
  • Gamma decay commonly produces energies of a few hundred keV, and almost always less than 10 MeV.
  • They are classically produced by the decay from high energy states of atomic nuclei, a process called gamma decay, but are also created by other processes.
  • Exceptions to this convention occur in astronomy, where gamma decay is seen in the afterglow of certain supernovas, but other high energy processes known to involve other than radioactive decay are still classed as sources of gamma radiation.

• Lasers

  • An electron in an excited state may decay to an unoccupied lower-energy state according to a particular time constant characterizing that transition.
  • When such an electron decays without external influence, it emits a photon; this process is called "spontaneous emission. " The phase associated with the emitted photon is random.
  • This "induced" decay process is called stimulated emission.
  • In stimulated emission, the decaying atom produces an identical "copy" of the incoming photon.
  • Therefore, after the atom decays, we have two identical outgoing photons.

• Half-Life and Rate of Decay; Carbon-14 Dating

  • Carbon-14 has a relatively short half-life of 5,730 years, meaning that the fraction of carbon-14 in a sample is halved over the course of 5,730 years due to radioactive decay to nitrogen-14.
  • Both processes of formation and decay of carbon-14 are shown in .
  • Thereafter, the concentration (fraction) of 14C declines at a fixed exponential rate due to the radioactive decay of 14C.
  • Diagram of the formation of carbon-14 (1), the decay of carbon-14 (2), and equations describing the carbon-12:carbon-14 ratio in living and dead organisms