Chapter 7.Nuclear Physics

What this covers? Inside the atom Discovery of the nucleus Types of radiation Nuclear reactions Half life Radioactivity in medicine Nuclear Reactions – fission and fusion

INSIDE THE ATOM

What is the modern model of the atom? The nucleus is where most of the mass of the atom is found. It contains protons and neutrons. The electrons orbit the nucleus in layers called shells. electron neutron proton Charge Mass Particle 1 +1 1 almost 0 -1

Nuclear Notation In the periodic table, there are two numbers found with each element. What do these numbers represent? Mass number is the number of protons + the number of neutrons. Atomic number (or proton number) is the number of protons

mass number is different atomic number is the same Isotopes? All carbon atoms have the same number of protons, but not all carbon atoms are identical. Although atoms of the same element always have the same number of protons, they can have different numbers of neutrons. Atoms that differ in this way are called isotopes. mass number is different atomic number is the same Isotopes tend to be unstable – these are the nuclei which are usually “radioactive”

Discovery of the nucleus

What was Rutherford’s involvement? Teacher notes This four-stage historical sequence explains Ernest Rutherford’s involvement in discovering the structure of the atom.

What did Geiger and Marsden do? Teacher notes This virtual experiment illustrates the experiment Geiger and Marsden used to get the results that led Rutherford to suggest his model of the atom. The components of the apparatus are broken down followed by the virtual experiment where the radiation detector can be moved to show the sort of results Geiger and Marsden would have got.

What were Geiger and Marsden’s results? The results of Geiger and Marsden’s experiment were: 2. Some alpha particles were slightly deflected by the gold foil. 1. Most alpha particles went straight through the gold foil, without any deflection. 3. A few alpha particles were deflected back from the gold foil. The experiment was carried out in a vacuum, so deflection of the alpha particles must have been due to the gold foil.

How did Rutherford interpret the results? Rutherford had expected all the alpha radiation to pass through the gold foil. He was surprised that some alpha particles were deflected slightly or bounced back. The ‘plum pudding’ model could not explain these results, so Rutherford proposed his ‘nuclear’ model of the atom. He suggested that an atom is mostly empty space with its positive charge and most of its mass in a tiny central nucleus. Electrons orbited this nucleus at a distance, like planets around the Sun.

How did Rutherford explain the results? Teacher notes This four-stage animation shows how Geiger and Marsden’s experiment gave the results it did, and why Rutherford’s atomic structure model is supported by the results of the experiment.

Atomic structure – key words Teacher notes This matching activity could be used as a plenary or revision exercise on atomic structure. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.

Nuclear Radiation

What is alpha (α) radiation? Boardworks GCSE Science: Physics Radioactivity 2 neutrons, 2 protons Description Note:– An alpha particle is the same as a helium nucleus Electric charge +2 4 Relative atomic mass Stopped by paper or a few centimetres of air Penetrating power Ionizing effect Strongly ionizing Effect of magnetic/ electric field Weakly deflected

What is beta (β) radiation? Boardworks GCSE Science: Physics Radioactivity Description High energy electron Electric charge -1 Relative atomic mass 1/1860 Penetrating power Stopped by a few millimetres of aluminium Ionizing effect Weakly ionizing Effect of magnetic/ electric field Strongly deflected

Boardworks GCSE Science: Physics Radioactivity Gamma () radiation Description High energy electromagnetic radiation Electric charge Relative atomic mass Penetrating power Stopped by several centimetres of lead or several metres of concrete Ionizing effect Very weakly ionizing Effect of magnetic/ electric field Not deflected

Teacher notes This activity, summarising the three types of radiation, could be used to introduce the topic of radiation, as a plenary exercise or as a revision exercise.

Teacher notes This true-or-false activity could be used as a plenary or revision exercise on the dangers of radiation, or at the start of the lesson to gauge students’ existing knowledge of the subject matter. Coloured traffic light cards (red = false, yellow = don’t know, green = true) could be used to make this a whole-class exercise.

Boardworks GCSE Science: Physics Radioactivity Teacher notes This matching activity could be used as a plenary exercise on the penetrating power of radiation. Students could be asked to complete the activity in their books or on mini-whiteboards. The activity could be concluded by completion on the IWB.

Boardworks GCSE Science: Physics Radioactivity Teacher notes This matching activity could be used as a plenary exercise on the range in air of the three types of radiation. Students could be asked to complete the activity in their books or on mini-whiteboards. The activity could be concluded by completion on the IWB.

Half Life

What happens to radioactivity? Teacher notes This five-stage animation explains why radioactivity decreases over time.

How is half-life calculated? Teacher notes This four-stage animation explains about half-life and how to calculate it from a decay curve graph.

What is half-life? The half-life of a radioactive element is the time that it takes half the atoms in a sample to decay. For example, the half-life of the isotope iodine-131 is 8 days. After 8 days = ½ remains After 16 days = ¼ remains After 24 days = 1/8 remains And so on….

What is the half-life of carbon-14? Teacher notes This animated graph can be used as a real-life example of a decay curve, and how to work out half-life. After the decay curve has animated, students could work individually or in small groups to calculate the half-life of carbon-14, and the activity could be concluded by completion on the IWB.

141 60 hours

RADIOACTIVE DECAY

Types of radioactive decay

What happens during alpha decay? An alpha particle consists of two protons and two neutrons. It is the same as a helium nucleus. When an atom’s nucleus decays and releases an alpha particle, it loses two protons and two neutrons. mass number decreases by 4 238 92 234 90 2 4  U Th + α atomic number decreases by 2 The number of protons has changed, so the decayed atom has changed into a new element.

What happens during beta decay? An beta particle consists of a high energy electron, which is emitted by the nucleus of the decaying atom. When an atom’s nucleus decays and releases a beta particle, a neutron turns into a proton, which stays in the nucleus, and a high energy electron, which is emitted. mass number remains the same 14 6 7  C N + β atomic number increases by 1 The decayed atom has gained a proton and so has changed into a new element.

Radioactive decay – true or false? Teacher notes This true-or-false activity could be used as a plenary or revision exercise on radioactive decay, or at the start of the lesson to gauge students’ existing knowledge of the subject matter. Coloured traffic light cards (red = false, yellow = don’t know, green = true) could be used to make this a whole-class exercise.

Radioactivity at Work

Boardworks GCSE Science: Physics Radioactivity Teacher notes This drag and drop activity could be used as a plenary exercise to check students’ knowledge of everyday uses of radiation. Class voting or the use of coloured traffic light cards could make this a whole-class exercise.

Teacher notes This true-or-false activity could be used as a plenary or revision exercise on everyday uses of radiation, or at the start of the lesson to gauge students’ existing knowledge of the subject matter. Coloured traffic light cards (red = false, yellow = don’t know, green = true) could be used to make this a whole-class exercise.

Nuclear Reactions

Fission When fission of uranium-235 occurs, it splits into two smaller nuclei, known as daughter nuclei. Many possible daughter nuclei may be formed in a fission process. One example is shown below. +  neutron uranium235 strontium90 xenon144 fission neutrons uranium 236 By the end of the lesson: State the products and reactants of fission reactions. Describe the processes using correct terminology. Apply your knowledge of the reactions to model them.

KE OF NUCLEI RISES RAPIDLY SO RAPID TEMPERATURE RISE Chain Reaction If the FAST neutrons produced in the reaction could be slowed down then they could be used to induce further fission in other U-235 atoms. Graphite (CARBON) MODERATOR Collision with C atoms slows down the fast neutrons KE OF NUCLEI RISES RAPIDLY SO RAPID TEMPERATURE RISE

Check point. a. These neutrons go on to collide with other nuclei causing a chain reaction b. The Uranium-235 nucleus splits c. Energy is released d. Neutrons are released e. A neutron hits a Uranium-235 nucleus.

Nuclear fission – true or false? Boardworks GCSE Additional Science: Physics Nuclear Energy Nuclear fission – true or false? Teacher notes This true-or-false activity could be used as a plenary or revision exercise on nuclear fission, or at the start of the lesson to gauge students’ existing knowledge of the subject matter. Coloured traffic light cards (red = false, yellow = don’t know, green = true) could be used to make this a whole-class exercise. By the end of the lesson: State the products and reactants of fission reactions. Describe the processes using correct terminology. Apply your knowledge of the reactions to model them.

Nuclear Reactor Fission Image from: http://www.freedomforfission.org.uk/sci/reactor.html courtesy of http://www.world-nuclear.org/ Fission

Chain reactions – key words Boardworks GCSE Additional Science: Physics Nuclear Energy Chain reactions – key words Teacher notes This matching activity could be used as a plenary or revision exercise on chain reactions. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.

Teacher notes This two-stage animated sequence explains how nuclear fusion occurs in a fusion reactor. By the end of the lesson: State what is meant by nuclear fusion. Describe the process and complete a nuclear equation for it. Identify the limitations with using fusion as an energy source and compare these with fission.

What are the conditions for nuclear fusion? In nuclear fusion, small nuclei fuse together to form larger nuclei and energy is released. +  tritium deuterium helium neutron fusion Nuclear fusion happens all the time in stars at very high pressures and temperatures. These conditions overcome repulsive forces between the nuclei and force them together. By the end of the lesson: State what is meant by nuclear fusion. Describe the process and complete a nuclear equation for it. Identify the limitations with using fusion as an energy source and compare these with fission.

Pros and cons of using nuclear fusion Boardworks GCSE Additional Science: Physics Nuclear Energy Pros and cons of using nuclear fusion Teacher notes Appropriately coloured voting cards could be used with this classification activity to increase class participation. By the end of the lesson: State what is meant by nuclear fusion. Describe the process and complete a nuclear equation for it. Identify the limitations with using fusion as an energy source and compare these with fission.