Nuclear Chemistry Chapter 18

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

Types of Radiation Alpha emission or decay (a) –helium atom 42He 23892U  42He + 23490Th Beta emission or decay (b)– 0-1e in the products 23490Th  23491Pa + 0-1e Gamma emission or decay (g) - 00g 23892U  42He + 23490Th + 00g

Types of Radiation & Particles Positron emission or decay - 0+1e 2211Na  0+1e + 2210Ne Electron capture – beta particle in the reactants 20180Hg + 0-1e  20179Au Neutron emission or decay– 10n 20984Po  10n + 20084Po Proton – 11H or 11p

Balancing Nuclear Equations Mass # and the atomic # totals must be the same for reactants and the products. 3919K  3517Cl + ___ 20682Pb  0-1e + ___ 23894Pu + ___ 42He + 23592U

Writing Balanced Nuclear Equations 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

Half-Life and Nuclear Stability 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.

Sample Half-lives Isotopes Half-Live Carbon – 14 5730 years Sodium – 24 15 hours Bismuth – 212 60.5 seconds Polonium – 215 0.0018 seconds Thorium – 230 75400 years Thorium – 234 24.1 days Uranium – 235 7.0 x 108 years Uranium – 238 4.46 x 109 years

Half-life sample problems 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?

Half-life sample problems How many days will it take 50 grams of Radon – 222 (half-life of 3.82 days) to decay to 3.125 grams?

Half-life sample problems 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?

Predicting radiation types from Reaction Products 238U  234Th  234Pa  234U α β β 234U  230Th  226Ra  222Rn  218Po  214Pb α α α α α 214Pb 214Bi 214Po 210Pb 210Bi 210Po206Pb β β α β β α

Scientists who shaped Nuclear Chemistry Henri Becquerel 1852- 1908 Discovered Natural Radioactivity - Nobel Prize (physics) 1903 Wilhem Roentgen 1845- 1923 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

Medical Applications of Nuclear Chem. 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

Scientists who shaped Nuclear Chemistry Pierre Curie 1859- 1906 Nobel Prize (physics) 1903 Ernest Rutherford 1871- 1937 Demonstrated the existence of the nucleus Nobel Prize (chemistry) 1908

Fission Nuclear fission was discovered in late 1930’s when U-235 was bombarded with neutrons and observed to split into two lighter elements. 10n + 23592 U  9236Kr + 14156Ba + 310n Energy from combustion of 1 mole of U-235 produces 26 million times as much energy as the combustion of 1 mole of methane.

Fission 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.

Critical State of a Fission 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 Sate of a Fission Reaction 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.

Sample fission reaction

Nuclear Fusion Fusion – combining two smaller nuclei into one heavier, more stable nucleus. 32He + 11H  42He + 01e Fusion reaction produce more energy than fission reactions. Fusion reactions are most commonly seen in stars.

Nuclear Fusion 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.

Sample fusion reaction

Effects of Radiation 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.

Effects of Radiation 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.