Chapter 16 Radioactivity

Radioactivity Section 1 Some atomic nuclei emit invisible energy known as radioactivity. Radioactivity Section 1

Discovering Radioactivity In 1896, a French scientist founded a new area of science when he discovered that some substances give off energy in the form of radioactive particles and rays. Nuclear radiation is energy that is created whenever atomic nuclei emit high energy particles and rays. During radioactivity, also known as radioactive decay, an unstable nucleus gives off energy and particles. Depending on the type of particle emitted, there are 3 types of radioactive decay. Alpha decay-an alpha particle made of 2 protons and 2 neutrons is released. As protons and neutrons are being emitted, the identity of the element changes. Beta decay-a beta particle consisting of either a positron or an electron is emitted or a neutron that immediately breaks down into an electron and a proton is emitted. RESULTS IN THE IDENTITY OF THE ELEMENT CHANGING! Gamma decay-a gamma-ray, which is a high energy light wave, is released as particles within the nucleus shift around. DOES NOT CREATE A NEW ELEMENT!

THE PENETRATING POWER OF RADIATION Each type of decay (alpha, beta, gamma) has a different mass and charge. With varying masses and charges, the decay types have different abilities to penetrate matter. As radioactive decay particles hit matter they can break chemical bonds and/or strip electrons off of atoms. This causes damage to matter. Each type of decay is able to pass through different materials. Alpha-paper Beta-Aluminum Gamma-Thick Lead THE PENETRATING POWER OF RADIATION

Radioactive elements decay at a set rate Radioactive elements decay at a set rate. This set rate can be used to determine the age of any organism that contains the radioactive element. Each radioactive substance has its own rate of decay. A half-life is the time it takes for ½ of the nuclei in the sample element (mother element) to decay and become a nuclei of a new element (daughter element). Scientists measure the number of decay cycles that a sample of an element has gone through in order to determine the age of the sample. Finding a date by decay

Carbon-14 has a half-life of 5,730 years Carbon-14 has a half-life of 5,730 years. That means that after 5,730 years, ½ of the nuclei in the sample have undergone decay. After 2 half-lives, 75% of the nuclei have undergone decay. Uranium-238 has a half-life of 4.5 billion years. This means that after 4.5 billion years, ½ the nuclei present in the sample have undergone decay. After 2 half-lives 75% have undergone decay. Finding a date by decay

Energy from the nucleus Getting energy from the nucleus of an atom has benefits and hazards. There are 2 ways to get energy from atomic nuclei: fission and fusion Energy from the nucleus

FISSION means DIVISION Fission is the process by which a large nucleus splits forming 2 smaller nuclei. This splitting of the nucleus results in a release of energy. The energy released during fission is a result of some of the mass of the original nucleus being converted into energy. FISSION means DIVISION Nuclear fission

Advantages and disadvantages of fission An uncontrolled fission reaction can lead to accidents where large amounts of radioactivity are released into the environment. This is a major concern at nuclear power plants. Fission reactions result in large amounts of radioactive waste. The safe disposal of the waste is difficult. A disadvantage of fission power plants that they are expensive to build. An advantage of a fission power plant is that it costs less to run than other types of energy producing plants. Fission power plants do not produce harmful greenhouse gases like fossil fuel plants do Advantages and disadvantages of fission

In a fusion reaction, 2 or more small nuclei are fused to form a larger nucleus. Very, very high temperatures are needed to overcome the repulsion the 2 positive nuclei have for each other. At the high temperatures needed for fusion to occur, matter is in the plasma state. As with fission, some of the nuclei matter is converted into energy and released. Nuclear fusion

Advantages and disadvantages of Fusion Requires very high temperatures, which required a lot of energy. We cannot currently do man-made fusion reactions. The waste after the reaction is not radioactive. Hydrogen is the fuel for the reaction. There is enough hydrogen in Earth’s waters to provide fuel for missions of years. Advantages and disadvantages of Fusion