Chapter 18

 Mass # Symbol  Element Name or symbol – Mass #  Parts of a Reaction Reactants  Products

 Alpha emission or decay (  ) –helium atom 4 2 He  U  4 2 He Th  Beta emission or decay (  )– 0 -1 e in the products  Th  Pa e  Gamma emission or decay (  )   U  4 2 He Th 

 Positron emission or decay e  Na  0 +1 e Ne  Electron capture – beta particle in the reactants  Hg e  Au  Neutron emission or decay– 1 0 n  Po  1 0 n Po  Proton – 1 1 H or 1 1 p

 Mass # and the atomic # totals must be the same for reactants and the products.  K  Cl + ___  Pb  0 -1 e + ___  Pu + ___  4 2 He U

 Alpha decay of Cu-68  Gamma emission of Thorium-235  Positron emission of P-18  Astatine-210 releasing 3 neutrons  Electron capture of Ti-45

 Radioactive isotopes or nuclides all decay because they are unstable, some just breakdown much faster than others  Half-life – amount of time for half of the original sample to decay  For two samples of the same isotope, regardless of the sample size, after one half- life, only half of the original amount of sample remains.

 IsotopesHalf-Live  Carbon – years  Sodium – 2415 hours  Bismuth – seconds  Polonium – seconds  Thorium – years  Thorium – days  Uranium – x 10 8 years  Uranium – x 10 9 years

 Barium – 139 has a half-life of 86 minutes. If you originally have a 10 gram sample of Barium-139, how much will be left after 258 minutes? 

 How many days will it take 50 grams of Radon – 222 (half-life of 3.82 days) to decay to grams?

 If a sample of Cesium-135 decays from 10 grams to 2.5 grams over a period of 84 days, what is the half-life of Cesium-135?

 238 U  234 Th  234 Pa  234 U  α β β  234 U  230Th  226 Ra  222 Rn  218 Po  214 Pb  α α α α α 214 Pb  214 Bi  214 Po  210 Pb  210 Bi  210 Po  206 Pb  β β α β β α

 Henri Becquerel Discovered Natural Radioactivity - Nobel Prize (physics) 1903  Wilhem Roentgen Discovered X- rays (1895) - Nobel Prize (physics) 1901  Marie (Sklowdowska) Curie 1867 – 1934 Discovered Radium and Polonium - (2) Nobel Prizes (physics) 1903, Chemistry (1911) – first woman to teach at the Sorbonne in its 650 yr history, first person to receive two Nobel prizes, only person to receive 2 Nobels in Sciences

 Pierre Curie Nobel Prize (physics) 1903  Ernest Rutherford Demonstrated the existence of the nucleus Nobel Prize (chemistry) 1908

 Cancer Radiation Treatment  Computer Imaging techniques  Radiocarbon dating  Smoke detectors  Food irradiation  Radioactive tracers – Iodine 131 used to treat thyroid illnesses and Thallium -201 can be used determine the damage done to someone’s heart by a heart attack

 Nuclear fission was discovered in late 1930’s when U-235 was bombarded with neutrons and observed to split into two lighter elements.  1 0 n U  Kr Ba n  Energy from combustion of 1 mole of U-235 produces 26 million times as much energy as the combustion of 1 mole of methane.

 The neutrons are produced from fission reactions, will then react with other radioactive atoms, which will produce more neutrons and so on, potentially creating an uncontrollable chain reaction.

 If reaction produces < 1 neutron on average, the nuclear fission stops over time.  If reaction produces exactly 1 neutron for each fission, the process is self-sustaining and is said to be critical.  If reaction produces > 1 neutron from each fission than the process can get out of control very quickly and cause a violent explosion.

 Critical mass = mass of fissionable material needed to keep fission reaction going, but at a safe level.  Hiroshima and Nagasaki bombs in 1945 were fission bombs where two subcritical masses were combined and have an extremely rapid fission reaction that causes a huge explosion.

 Fusion – combining two smaller nuclei into one heavier, more stable nucleus. 3 2 He H  4 2 He e  Fusion reaction produce more energy than fission reactions.  Fusion reactions are most commonly seen in stars.

 We have many potential sources for fusion reactions, but the problem lies in trying to slam two positively charged nuclei together with enough force to make them combine.  It is thought that the temperature must be over 40 million Kelvin for this to occur, which is where the speed of the particles could potentially overcome the repulsive forces.

 Somatic damage – done to the organism itself, resulting in either sickness or death.  Effect of somatic damage may be immediate or take years to show their effects, such as radiation treatment for cancer patients.  Genetic damage – damages cells which can be passed on to afflict offspring of initially effecting organism.

 Energy of radiation – higher energy = more damage (big surprise)  Penetrating ability of the radiation – gamma particles are high penetrating, beta can penetrate 1 cm and alpha particles can be stopped by the skin.