Radioactivity Nucleus – center of the atom containing protons and neutrons How are the protons and neutrons held together? Strong Force - an attractive force that holds protons and neutrons together The protons and neutrons must be close together for this force to keep them together As the nucleus increases in size, the strong force diminishes and the electrical force (force between charges) becomes more powerful

Radioactivity – process of nuclear (nucleus) decay Stability of Nuclei Larger nuclei are less stable – all nuclei that contain more than 83 protons are radioactive The ratio of neutrons to protons also determines if an element is radioactive Nuclei with too many or too few neutrons compared to protons are usually unstable, and thus, radioactive

C C Nucleus numbers representation A nucleus can be represented by the following isotope notation In this carbon-12 isotope, there are 6 protons and 6 neutrons, which makes it stable and not radioactive What would carbon-14 look like? Would carbon-14 be radioactive? Why? mass number C 12 element symbol 6 atomic number C 14 6 radioactive, because it has too many neutrons compared to its protons

Nuclear Radiation – when an unstable nucleus decays, particles and energy are emitted (given off) 3 types of Nuclear Radiation Alpha Particles Beta Particles Gamma Rays

Radioactivity Uses Treating cancer Internal inspection Radioactive dating of artifacts Tracing Smoke detectors Sterilization Food irradiation Thickness monitoring Nuclear energy

He Alpha Particles – made of 2 protons and 2 neutrons Also known as a helium-4 nucleus with a charge of 2+ (no electrons) As the alpha particle leaves the atom, it passes through other matter and takes electrons, leaving behind ions This process causes it to lose much of its energy An atomic mass unit of 4 can be stopped with a sheet of paper or clothing Symbol He 4 2

Transmutation – process of changing one element to another through nuclear decay - Alpha particle nuclear reaction During the transmutation, the total mass and charges of the nuclei at the end are the same as the nucleus at the beginning + Po 210 84 Pb 206 82 He 4 2 + +84 +82 +2

Beta Particles – a neutron decays into a proton and emits an electron in the process the beta particle has a negative charge Smallest of the radiation particles – has an atomic mass unit of 0.0005 Much faster and more penetrating than alpha particles Can be stopped by a sheet of aluminum foil or wood Symbol e -1

I Xe e Beta particle nuclear reaction - + During the transmutation, the total mass and charges of the nucleus and the electron emitted at the end are the same as the beginning - + I 131 53 Xe 131 54 e -1 + +53 +54 -1

Gamma Rays – electromagnetic wave usually emitted from a nucleus when an alpha decay or beta decay occurs gamma rays have no mass or charge and travel at the speed of light Deepest penetrating of radiation, but is not as damaging to living tissue as alpha and beta Requires dense, thick materials such as concrete blocks or lead to stop

Alpha particles have a greater charge and mass than beta particles and gamma rays do. Alpha particles travel about 7 cm through air and are stopped by paper or clothing. Beta particles have a 1 or 1 charge and almost no mass. They are more penetrating than alpha particles. Beta particles travel about 1 m through air but are stopped by 3 mm of aluminum. Gamma rays have no charge or mass and are the most penetrating. They are blocked by very dense, thick materials, such as a few centimeters of lead or a few meters of concrete.

Radioactive Half-life – the amount of time it takes for half of the nuclei in a sample of an isotope to decay Example, the half-life of (hydrogen-3) is 12.3 years. The H-3 will beta decay to He-3 If a sample has 20 atoms of hydrogen, after 12.3 years, 10 atoms will have decayed to He-3, and the other 10 will still be H-3 After 12.3 more years, another 5 will have decayed to He-3, and 5 will still be H-3 H 3 1

Radioactive Dating – using known half-lives to date certain rocks, fossils, and other materials Carbon dating – radioactive isotope carbon- 14 is found in plants and animals. Has a half-life of 5,730 years Used to get the approximate age of plants and animals up to 50,000 years Uranium Dating – used to date some rocks that contain small amounts of uranium

Solving Half-Life problems Make a HMT, chart like shown: H=Half Lives M=Mass T=Time %= per cent left Fraction=fraction left For the mass, divide by two for each half life For the time, add the half life time.

A. Potassium-42 has a half-life of 12. 4 hours A. Potassium-42 has a half-life of 12.4 hours. How much of an 848 g sample of potassium-42 will be left after 62.0 hours? B. If the half-life of iodine-131 is 8.10 days, how long will it take a 50.00 g sample to decay to 6.25 g? C. What is the half-life of a 100.0 g sample of nitrogen-16 that decays to 12.5 g of nitrogen-16 in 21.6 s?

Nuclear Reactions Make sure the atomic numbers are and the mass numbers are equal on either side of the arrow.

Nuclear Reactions Nuclear Fission – The process of splitting a nucleus into several smaller nuclei Only large nuclei, such as uranium and plutonium, undergo fission A neutron collides with a large nucleus and splits in two Some of the mass actually converts to a tremendous amount of energy Kr 90 36 n + energy n n U 235 92 Ba 142 56 n

Chain Reaction - When a nuclear fission reaction occurs, the neutrons emitted can strike other nuclei in the sample, and cause them to split. Critical mass - the amount of material needed to sustain a chain reaction.

Nuclear Power – Fission How a Fission Nuclear Power Plant Works Energy comes from a controlled fission nuclear reaction Uses Uranium -235 As the nuclei split, tremendous heat is released Heat is used to produce steam that turns a turbine which rotates an electric generator n + 1 U 235 92 Sn + Mo + n 132 101 50 42 3

Nuclear Power – Fission Advantages does not release pollutants like fossil fuels provides about a million times more energy per pound than fossil fuels Disadvantages radioactive material could be released into environment in an accident disposal of waste material is expensive and difficult uranium is non- renewable

Nuclear Fusion – two nuclei of smaller mass are combined to form one larger nucleus Produces even more energy than fission Temperature must be extremely hot (millions of degrees Celsius) for nuclei to be moving so fast that they get close enough for fusion to occur H-1 + energy He-3 H-2

Nuclear Power – Fusion How Fusion Nuclear Power Works Fusion of 2 small nuclei Hydrogen nuclei fuse to form Helium Must occur at extremely high temperatures Releases huge amounts of energy, even more than fission reactions H + 1 e -1 He 4 2

Nuclear Power – Fusion Advantages Disadvantages uses hydrogen as a fuel which is very abundant on earth the product is helium, a non-radioactive and non-polluting element most concentrated energy source known Disadvantages occurs only at high temps of millions of degrees Celsius use more energy to produce the reaction than energy given off containment of the reaction will be extremely difficult