P6 radioactive-decay


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P6 radioactive-decay

  1. 1. Lesson 5: Radioactive decayWhat you need to know: 1. The structure of an atom. 2. Understand the process of radioactive decay. 3. What the three types of radioactive decay. An atom of any element is made of three tiny particles: protons, neutrons and electrons. The nucleus of the atom contains protons and neutrons and the number of protons in the nucleus defines what type of element the atom is. For example, all atoms of Carbon have 6 protons (the atomic number) and all atoms of nitrogen have 7 protons. Nearly all the mass of the atom is concentrated in the nucleus. Orbiting around the nucleus is a shell of electrons, which are usually equal in number to the number of protons. Electron Neutron Proton Nucleus In your exam you may be asked to explain the structure of an atom. If you look at a periodic table, you may have noticed that the relative atomic mass (the number in the top left hand corner), is not always a whole number. The reason for this is that not all atoms of the same element have the same number of neutrons. Atoms of the same element with different amounts of neutrons are called isotopes, for example: 1. There are two possible isotopes of oxygen, Oxygen-17 (9 neutrons) and Oxygen-18 (10 neutrons). These two atoms are isotopes of oxygen and all must have 8 protons, but each has a different number of neutrons. © Studydoctor 2009
  2. 2. 2. There are two isotopes of carbon, Carbon-11 (5 neutrons) and Carbon-14 (8 neutrons). These two atoms are isotopes of carbon and have 6 protons, but have different numbers of neutrons. In your exam you may be asked what an isotope is.Certain atoms emit ionizing radiation because their nucleuses are unstable andthey can decay (change). This is called radioactive decay and this is a changeinside the nucleus of the atom.There are three different types of radioactive decayType of decay What is emitted What is happeningAlpha (α) A helium nucleus (2 The nucleus decays, ejecting an protons and 2 Alpha particle. A new atom is neutrons). This is called formed which contains two fewer an alpha particle in protons and neutrons. This new radioactive decay. atom is a different element to the one you started with.Beta (β) A high speed electron. The nucleus decays, changing a neutron into a proton and an electron. A new atom is formed with 1 less neutron and 1 more proton. This new atom is a different element to the one you started with.Gamma (γ) Electromagnetic Sometimes an atom simply contains radiation too much energy which it needs to emit, so it gives off a Gamma ray. The nucleus remains unchanged.Alpha decay New nucleus Alpha particle Unstable nucleus © Studydoctor 2009
  3. 3. Beta decay New nucleus Beta particle Unstable nucleus Gamma decay Unstable nucleus Gamma wave In your exam you may be asked to identify and explain the three different types of radioactive decay. When an element occurs in a form where its nucleus is unstable, leading to radioactive decay, it is called a radioactive isotope. Radioactive isotopes are used in hospitals to produce scans and to cure diseases, but radioactive isotopes are hard to find naturally, as they have decayed. Therefore, hospitals get supplies of radioactive isotopes from nuclear reactors, where radioactive isotopes are a by-product of the processes that are happening in a nuclear reactor. In your exam you might be asked to describe what a radioactive isotope is. You may also be asked where hospitals get their supplies of radioactive isotopes.Recap: 1. An atom has a nucleus which contains protons and neutrons and has a shell of electrons orbiting around the nucleus. 2. Isotopes are atoms of the same element, which have different numbers of neutrons. 3. Radioactive decay occurs when unstable atoms decay, emitting ionizing radiation. 4. There are three different types of radioactive decay, Alpha (α), Beta (β) and Gamma (γ). © Studydoctor 2009