Slide 4 of 11 Nuclear vs. Chemical Nuclear reactions do not follow the same rules that chemical reactions do For example, in a nuclear reaction matter can be created or destroyed. They are not affected by temperature, pressure or catalysts, and they cannot be speeded up, slowed down or turned off.
Slide 5 of 11 Discovery of Radioactivity In 1896, Antoine Henri Becquerel, noticed that photographic film would fog when it was exposed to Uranium salts. He had two assistants, Marie Curie and Pierre Curie, were able to show that the fogging was caused by rays emitted from the Uranium atoms in the ore. Marie Curie named the process by which materials give off such rays Radioactivity. The rays and particles that are given off are called radiation. This discovery tore apart Dalton’s theory of an indivisible atom.
Slide 6 of 11 Image of Becquerel's photographic plate which has been fogged by exposure to radiation from a uranium salt. The shadow of a metal Maltese Cross placed between the plate and the uranium salt is clearly visible.Maltese Cross
Slide 7 of 11 We are going to be studying three types of radiation. Alpha ( )(Positive) Beta ( )(Negative) Gamma ( )(No charge)
Slide 8 of 11 Radioactive Decay Three common types of radioactive decay TypeParticle Relative Size Relative Energy Alpha 4 2 He LargeLow Beta 0 +1 e Effectively none Medium GammaNot a particleHigh
Slide 9 of 11 Alpha Particles Alpha radiation consists of helium nuclei that have been emitted from a radioactive source. These emitted particles, alpha particles, contain two protons and two neutrons, and have a 2+ charge. However, when writing a nuclear reaction, the electric charge is generally omitted. Alpha particles are either written as 4 2 He or .
Slide 10 of 11 Alpha 238 92 U 234 90 Th + 4 2 He ( )
Slide 11 of 11 Beta Particles Beta radiation consists of fast moving electrons formed from the decomposition of a neutron in an atom. The neutron (no charge) decomposes into a proton, which remains in the nucleus, and an electron, which is released. 1 0 n 1 1 H + 0 -1 e (beta particle) The fact that the particle is negatively charged is reflected in the subscript –1, where the atomic number is generally written. The virtual lack of mass is expressed in the superscript 0, corresponding to the mass number.
Slide 12 of 11 Beta 137 55 Cs 137 56 Ba + 0 -1 e
Slide 13 of 11 Gamma Radiation Gamma radiation is high energy electromagnetic radiation given off by radioisotopes. Visible light is also part of the electromagnetic spectrum, but much lower in energy. Gamma rays are often emitted along with alpha or beta radiation by the nuclei of disintegrating radioactive atoms. Gamma rays have no mass or electrical charge, therefore, the emission of gamma radiation does not alter the atomic number or mass number of an atom.
Slide 17 of 11 Energy from fission Nuclear fission releases a lot of energy. In fact, the fission of 1 kg of Uranium-235 releases as much energy as 20000 tons of dynamite. In an uncontained reaction, this occurs in only a fraction of a second. Atom bombs are devises that start uncontrolled nuclear chain reactions
Slide 18 of 11 Energy from Fusion The energy that the sun gives off comes from nuclear fusion. Fusion occurs when nuclei combine to produce a nucleus of greater mass. In solar fusion, Hydrogen nuclei (protons) fuse to form Helium nuclei, it also requires 2 beta particles. Fusion releases more energy than Fission, however, it can only occur at temperatures in excess of 40,000,000°C.
Slide 19 of 11 Relative Energies ProcessEnergy H 2 O (l) H 2 O (g) 40.7 kJ/mol H 2 O (g) H 2(g) + ½ O 2(g) 241.8 kJ/mol H 2 H + H 432 kJ/mol 2 1 H + 2 1 H 4 2 H e 2.5 x 10 9 kJ/mol
Slide 20 of 11 Half-Life Every radioisotope has a characteristic rate of decay that is called a half-life. The half-life of a substance is the time required for half of the nuclei of a radioactive substance to decay into it’s products. The second half-life will leave you with ¼ of your original sample. The third half-life will leave you with 1/8 of your original sample. Half-lives can be a short as a fraction of a second or as long as billions of years. Carbon-dating uses the half-life of Carbon-14 in order to date old artifacts.
Slide 21 of 11 Radioactive Half-life Half-life: The time it takes for half the material to decay. Link to Applet