half-life

(noun)

The time it takes for half of the original concentration of an isotope to decay back to its more stable form.

Related Terms

  • nuclide
  • allotropes
  • radiometric dating
  • radioactive isotopes
  • radiocarbon dating
  • isotope

(noun)

The time required for half of the nuclei in a sample of a specific isotope to undergo radioactive decay.

Related Terms

  • nuclide
  • allotropes
  • radiometric dating
  • radioactive isotopes
  • radiocarbon dating
  • isotope

(noun)

The time required for a quantity to fall to half its value as measured at the beginning of the time period.

Related Terms

  • nuclide
  • allotropes
  • radiometric dating
  • radioactive isotopes
  • radiocarbon dating
  • isotope

(noun)

In a radioactive decay process, the amount of time required to end up with half of the original (undecayed) material.

Related Terms

  • nuclide
  • allotropes
  • radiometric dating
  • radioactive isotopes
  • radiocarbon dating
  • isotope

Examples of half-life in the following topics:

  • Half-Life of Radioactive Decay

    • Given a sample of a particular radionuclide, the half-life is the time taken for half of its atoms to decay.
    • The half-life is related to the decay constant.
    • Half-lives vary widely; the half-life of 209Bi is 1019 years, while unstable nuclides can have half-lives that have been measured as short as 10−23 seconds.
    • This means each half-life for element X is 18 days.
    • Nuclear half-life is the time that it takes for one half of a radioactive sample to decay.
  • Half-Life

    • To find the half-life of the reaction, we would simply plug 5.00 s-1 in for k:
    • To find the half-life, we once again plug in $\frac{[A]_0}{2}$for [A].
    • Thus the half-life of a second-order reaction, unlike the half-life for a first-order reaction, does depend upon the initial concentration of A.
    • Rearranging in terms of t, we can obtain an expression for the half-life:
    • The half-life of a reaction is the amount of time it takes for it to become half its quantity.
  • Dating Using Radioactive Decay

    • After one half-life has elapsed, one half of the atoms of the nuclide in question will have decayed into a "daughter" nuclide, or decay product.
    • Each step in such a chain is characterized by a distinct half-life.
    • The half-life of Cs-137 is 30 years.
    • First half-life (30 years): 100 grams of Cs-137 decays and 50 grams are left.
    • Calculate the age of a radioactive sample based on the half-life of a radioactive constituent
  • Transuranium Elements

    • Each of these elements is radioactive, with a half-life much shorter than the age of the Earth.
    • Yellow - Radioactive elements: the most stable isotope has a half-life between 800 and 34.000 years.
    • Orange - Radioactive elements: the most stable isotope has a half-life between one day and 103 years.
    • Red - Highly radioactive elements: the most stable isotope has a half-life between several minutes and one day.
    • Purple - Extremely radioactive elements: the most stable isotope has a half-life less than several minutes.
  • Zero-Order Reactions

    • The half-life of a reaction describes the time needed for half of the reactant(s) to be depleted, which is the same as the half-life involved in nuclear decay, a first-order reaction.
    • For a zero-order reaction, the half-life is given by:
  • Rate of Radioactive Decay

    • Radioactive decay rate is exponential and is characterized by constants, such as half-life, as well the activity and number of particles.
    • The half-life (t1/2) is the time taken for the activity of a given amount of a radioactive substance to decay to half of its initial value.
    • Find the decay rate ($\lambda$) of element X, with a half-life of 2350 years.
    • Since we are dealing with the half-life we will use values for N and No that are equivalent to 0.5.
  • Isotopes of Hydrogen

    • The most stable radioisotope of hydrogen is tritium, with a half-life of 12.32 years.
    • All heavier isotopes are synthetic and have a half-life less than a zeptosecond (10-21 sec).
    • It has a half-life of 12.32 years.
    • It decays through neutron emission with a half-life of 1.39 ×10−22 seconds.
    • 6H decays through triple neutron emission and has a half-life of 2.90×10−22 seconds.
  • Isotopes

    • After approximately 5,730 years, half of the starting concentration of 14C will have been converted back to 14N.
    • This is referred to as its half-life, or the time it takes for half of the original concentration of an isotope to decay back to its more stable form.
    • Because the half-life of 14C is long, it is used to date formerly-living objects such as old bones or wood.
    • Other elements have isotopes with different half lives.
    • For example, 40K (potassium-40) has a half-life of 1.25 billion years, and 235U (uranium-235) has a half-life of about 700 million years.
  • Properties of Carbon

    • Carbon compounds form the basis of all known life on Earth, and the carbon-nitrogen cycle provides some energy produced by the sun and other stars.
    • Identification of carbon in NMR experiments is done with the isotope 13C. 14C is a radioactive isotope of carbon with a half-life of 5730 years.
    • In total, there are 15 known isotopes of carbon and the shortest-lived of these is 8C, which decays through proton emission and alpha decay, and has a half-life of 1.98739 x 10−21 seconds.
  • Ozone

    • It is an allotrope of oxygen that is much less stable than the diatomic allotrope (O2), breaking down with a half life of about half an hour in the lower atmosphere to O2.
    • It is also unstable at high concentrations, decaying to ordinary diatomic oxygen (with a half-life of about half an hour in atmospheric conditions):
Subjects
  • Accounting
  • Algebra
  • Art History
  • Biology
  • Business
  • Calculus
  • Chemistry
  • Communications
  • Economics
  • Finance
  • Management
  • Marketing
  • Microbiology
  • Physics
  • Physiology
  • Political Science
  • Psychology
  • Sociology
  • Statistics
  • U.S. History
  • World History
  • Writing

Except where noted, content and user contributions on this site are licensed under CC BY-SA 4.0 with attribution required.