Long Age Isotope Decay Sequences (Sidebar 2)

Radioisotope decay is a process whereby an unstable atom spontaneously changes form to become more stable. The spontaneous change alters the composition of the atom. Following is a review of the composition of an atom and some examples of the most common long age isotope decay sequences that are used to date volcanic rocks. Composition of an atom: The nucleus is composed of protons and neutrons. Protons have positive charges, but neutrons are uncharged. Electrons are negatively charged particles with a mass near zero. Electrons move in orbits around the nucleus. The atomic mass of an atom is the sum of the total number of protons and neutrons. To be stable, an atom must have the same number of protons and electrons (equal positive and negative charges). The number of protons (which is equal to the number of electrons) is unique for each element and can be used to identify the element. The number of protons is commonly called the atom's Z number. The N number refers to the number of neutrons in the atom's nucleus. The N and Z numbers can be different in atoms of the same element. The Z number plus the N number is the Atomic mass. Examples:

Defining terms: 1. Isotopes—atoms of the same element, but with different neutron numbers (N numbers) rendering different atomic masses. For example, Carbon-12 and Carbon-14 are the same element because they have the same numbers of protons and electrons, and they are isotopes because Carbon-14 has two more neutrons than Carbon-12. 2. Radioisotopes—isotopes which are unstable and change form to more stable isotopes through a decay process. 3. Radioisotope decay—the spontaneous transformation of an unstable isotope to a different isotope or element with the release of rays or particles. (1) Alpha decay—the parent radioisotope loses alpha particles (helium nuclei). The alpha particles have mass, so the parent actually decreases in mass due to the loss of protons and neutrons and becomes another element. For example, uranium-238 loses an alpha particle and is converted to thorium-234. (2) Beta Decay—release of electrons which changes the element, but does not result in a substantial change in mass, so thorium-234, for example, would decay to protactinium-234, which changes to uranium-234, etc. The decay process continues through more intermediate stages until a stable isotope is formed. 4. Nuclear Decay Constant—"the probability that a radioactive parent atom will decay during a one year period of time" (Austin, 1994). Many radioactive isotopes used to date rocks have extremely low decay constants. For example the probability that one atom of Uranium-238 would decay to an atom of lead-206 in one year is 1.55125 x 10-10. 5. Half-life—The amount of time required for one half of the initial quantity of parent isotopes to be converted to the daughter isotope. If the nuclear decay constant of the radioactive isotope is low, the half-live is very long. For example, the half-life of Uranium-238 is 4.47 billion years.
The process of Isotope Decay: 1. Starting components—"parent" (unstable isotope) 2. Products—alpha particles (Helium nuclei), beta particles (electrons), intermediate isotopes stages, stable daughter isotope
The major long-age isotope decay sequences—
	1. Potassium-40 turns to Argon-40 (K/Ar) The isotope of potassium with an atomic mass of 40 (K-40) decays to argon-40 through beta decay (the release of electrons). This decay sequence has a half-life of 1.25 billion years. 2. Rubidium-87 turns to Strontium-87 (Rb/Sr) The isotope of rubidium that has an atomic mass of 87 decays to Strontium-87 through beta decay. This decay sequence has a half-life of 48.8 billion years. 3. Uranium-238 turns to Lead-206 (U/Pb) The isotope of uranium with an atomic mass of 238 (U-238 the parent) decays to Thoreum-234 by alpha decay. Thoreum-234 decays to Protactinium-234 to Uranium-234 through beta decay. Uranium-234 decays to Thoreum-230 to Radium-226 to Radon-222 to Polonium-218 to Lead-214 through alpha decay processes. Lead-214 decays to Bismuth-214 to Polonium-214 through beta decay processes. Polonium-214 decays to Lead-210 through alpha decay. Lead-210 decays to Bismuth-210 to Polonium-210 through Beta decay, and then to the stable daughter Lead-206 through alpha decay. The half life of the parent U-238 is 4.47 billion years. Reference Austin, S.A. 1994 "Are Grand Canyon rocks one billion years Old?" Grand Canyon: Monument to Catastrophe, Institute for Creation Research p. 113.