The normal activity of living carbon-containing matter is found to be about 15 decays per minute for every gram of carbon. This activity arises from the small proportion of radioactive C614C614 present with the stable carbon istope C612. When the organism is dead, its interaction with the atmosphere (which maintains the above equilibrium activity) ceases and its activity begins to drop. From the known half-life (5730 years) of C614, and the measured activity, the age of the specimen can be approximately estimated. This is the principle of C614 dating used in archaeology. Given, = 15 decays/min, Present activity R = 9 decays/min, Half life, T = 5730 years, Age t =? As, activity is proportional to the number of radioactive atoms, therefore, NN0 = RR0 = 915 But, NN0 = e-λt ∴ e-λt = 915 =35 e+λt = 53 ⇒ λt logee = loge53 = 2.3026 log 1.6667 ⇒ λt = 2.3026 × 0.2218 = 0.5109∴ t = 0.5109λ But, λ = 0.693T =0.6935730 Yr-1 Therefore,t =0.51090.693/5730 = 0.5109 × 57300.693 t = 4224.3 years. is the approximate age. Alpha particles — The nucleus of a helium atom, made up of two neutrons and two protons with a charge of +2. Certain radioactive nuclei emit alpha particles. Alpha particles generally carry more energy than gamma or beta particles, and deposit that energy very quickly while passing through tissue. Alpha particles can be stopped by a thin layer of light material, such as a sheet of paper, and cannot penetrate the outer, dead layer of skin. Therefore, they do not damage living tissue when outside the body. When alpha-emitting atoms are inhaled or swallowed, however, they are especially damaging because they transfer relatively large amounts of ionizing energy to living cells. See also beta particle, gamma ray, neutron, x-ray. Atom — The smallest particle of an element that can enter into a chemical reaction. Beta Particles — Electrons ejected from the nucleus of a decaying atom. Although they can be stopped by a thin sheet of aluminum, beta particles can penetrate the dead skin layer, potentially causing burns. They can pose a serious direct or external radiation threat and can be lethal depending on the amount received. They also pose a serious internal radiation threat if beta-emitting atoms are ingested or inhaled. See also alpha particle, gamma ray,neutron, x-ray. Decay Chain (Decay Series) — The series of decays that certain radioisotopes go through before reaching a stable form. For example, the decay chain that begins with uranium-238 (U-238) ends in lead-206 (Pb-206), after forming isotopes, such as uranium-234 (U-234), thorium-230 (Th-230), radium-226 (Ra-226), and radon-222 (Rn-222). Gamma Rays — High-energy electromagnetic radiation emitted by certain radionuclides when their nuclei transition from a higher to a lower energy state. These rays have high energy and a short wave length. All gamma rays emitted from a given isotope have the same energy, a characteristic that enables scientists to identify which gamma emitters are present in a sample. Gamma rays penetrate tissue farther than do beta or alpha particles, but leave a lower concentration of ions in their path to potentially cause cell damage. Gamma rays are very similar to x-rays. See also neutron. Isotope — A nuclide of an element having the same number of protons but a different number of neutrons. Neutron — A small atomic particle possessing no electrical charge typically found within an atom’s nucleus. Neutrons are, as the name implies, neutral in their charge. That is, they have neither a positive nor a negative charge. A neutron has about the same mass as a proton. See also alpha particle, beta particle, gamma ray, nucleon, x-ray. Radioactive Decay — Disintegration of the nucleus of an unstable atom by the release of radiation. Radiation — Energy moving in the form of particles or waves. Familiar radiations are heat, light, radio waves, and microwaves. Ionizing radiation is a very high-energy form of electromagnetic radiation. Radioactive Material — Material that contains unstable (radioactive) atoms that give off radiation as they decay. Radionuclide — An unstable and therefore radioactive form of a nuclide. [Back to Top]
This is a list of radioactive nuclides (sometimes also called isotopes), ordered by half-life from shortest to longest, in seconds, minutes, hours, days, and years. Current methods make it difficult to measure half-lives between approximately 10−19 and 10−10 seconds.[1] 10−24 seconds
23 yoctoseconds is the time needed to traverse a 7 femtometre distance at the speed of light, around the diameter of a large atomic nucleus. 10−21 seconds
10−18 seconds
10−15 seconds
10−12 seconds
10−9 seconds
10−6 seconds
10−3 seconds
seconds minutes seconds
Tellurium-128's half-life is over 160 trillion times greater than the age of the universe (which is 4,35*1017 seconds).[4]
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