Beta Emissions Principles of Carbon Dating 1 Radioactive

Beta Emissions (Principles of Carbon Dating) 1

Radioactive Emissions (Radiation) Radiation - Energy emitted in the form of waves (light) or particles (photons). Beta Radiation: emits a beta particle (an electron). In beta decay a neutron in the nucleus changes into a proton, an electron and a neutrino and ejects the high speed electron (beta particle) from the nucleus. . 2

Radioactive Emissions (Radiation) Type Description Equivalent Alpha Dense (+) charged particle (-) charged particle Helium nucleus Beta Gamma Type of energy High speed electron High energy photons 3 Symbol 4 2 He ( ) 0 -1 e 0 b -1 0 0 g Penetrating Power Stopped by thick paper Stopped by 6 mm of Al Stopped by several cm of Pb

Penetrating Power of Radioactive Emissions 4

Beta Decay When a parent nucleus decays by the Beta (β) decay process, an electron, called a beta particle (β) is emitted. The resulting daughter nucleus will always have the same atomic mass and an atomic number increased by one. atomic weight is constant emitted beta particle atomic number increases 5

Beta Decay A beta particle is created in the nucleus by a process in which one neutron is transformed into a proton and an electron. Example of Beta Decay: Mass: 14 = 14 + 0 14 = 14 Charge: 6 = 7 + (-1) 6 =6 6

Beta Decay Application – Carbon Dating Click here for a short video on carbon dating dead biological materials. How old are these bones? 7

Beta Decay Application – Carbon Dating Carbon dating is a method of determining the age of dead biological materials based on the rate of decay of the radioactive isotope Carbon-14. • Willard F. Libby pioneered carbon dating at the University of Chicago in the 1950's. • In 1960, he won the Nobel Prize for Chemistry for this work. • Radiocarbon dating is now the most widely used method of age estimation in the field of archaeology. 8

Beta Decay Application – Carbon Dating Carbon-14 is an unstable isotope of Carbon-12. 9

Beta Decay Application – Carbon Dating Carbon-14 begins when high-energy cosmic rays enter the earth's atmosphere. The rays collide with atoms to create a secondary cosmic rays in the form of an energetic neutron. (Every person on the earth is hit with about 500, 000 cosmic rays every hour. ) neutron cosmic ray atom 10

Beta Decay Application – Carbon Dating These neutrons can then collide with the diatomic nitrogen molecules in the atmosphere. These collisions produce carbon-14 and nitrogen atoms, as well as protons. neutron 11

Beta Decay Application – Carbon Dating Just like carbon-12, carbon-14 chemically reacts with the oxygen in the atmosphere to produce carbon dioxide. 12

Beta Decay Application – Carbon Dating Almost all of the carbon dioxide in our atmosphere is derived from non-radioactive carbon-12 atoms. The ratio of normal carbon-12 to carbon-14 in the air and in all living things is nearly constant at any given time. This ratio is approximately 1 in every in one trillion carbon atoms is carbon-14. 13

Beta Decay Application – Carbon Dating Like carbon dioxide made from xarbon-12, carbon dioxide made from carbon-14 enters the carbon cycle through photosynthesis. As animals eat plant life they assimilate both carbon-12 and carbon-14 into their bodies in the ratio that carbon-12 and carbon-14 exist in nature. The process of live organisms (including humans) taking in carbon continues until death. 14

Beta Decay Application – Carbon Dating Once an organism dies, it stops consuming Carbon and the amount of carbon-12 in the tissue remains constant. But, the carbon-14 that was in the tissue radioactively decay (with a haf-life of 5, 730 years) into nitrogen-14. 15

Beta Decay Application – Carbon Dating By measuring the ratio of c-12 to c-14 in a sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing. 16

Beta Decay Application – Carbon Dating The formula to calculate how old a sample is by carbon -14 dating is: t = [ln(Nf/No)/(-0. 693)]x t 1/2 where: ln is the natural logarithm Nf/No is the percent of carbon-14 in the sample compared to the amount in living tissue t 1/2 is the half-life of carbon-14 (5, 730 years) 17

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