Do now! Can you look through your books and read the comments? Can you also look through the tests and make sure that Mr Porter has added the marks up correctly?

Homework Set 13 th November Due 19 th November Use pages 202 to 223 to make REVISION CARDS for the electromagnetism topic. OPTIONAL for David and Harsh

Radioactivity

Last lesson describe the structure of an atom in terms of protons, neutrons and electrons and use symbols to describe particular nuclei understand the terms atomic (proton) number, mass (nucleon) number and isotope understand that ionising radiations can be detected using a photographic film or a Geiger- Muller detector recall the sources of background radiation

The atom orbiting electrons Nucleus (protons and neutrons)

Nuclide notation Li 3 7 Atomic number (proton number) = number of protons Atomic mass (mass number) = number of protons and neutrons

Isotopes Li 3 7 It is possible for the nuclei of the same element to have different numbers of neutrons in the nucleus (but it must have the same number of protons) Li 3 6

Isotopes Li 3 7 For example, Lithium atoms occur in two forms, Lithium-6 and Lithium-7 Li neutrons 3 neutrons

Relative atomic mass On average, lithium atoms have a mass of (relative to Carbon 12) Li

Unstable nuclei Some nuclei are unstable, for example Uranium 235 Hi! I’m uranium-235 and I’m unstable. I really need to lose some particles from my nucleus to become more stable.

Unstable nuclei To become stable, an unstable nuclei emits a particle Weeeeeeeeeeeeee!

Unstable nuclei We say the atom has decayed Weeeeeeeeeeeeee!

Unstable nuclei The decay of an unstable nucleus is random. We know it’s going to happen, but we can’t say when! It cannot be affected by temperature/pressure etc. Weeeeeeeeeeeeee!

Becquerels (Bq) The amount of radioactivity given out by a substance is measured in Becquerels. One becquerel is one particle emitted per second.

Detection Particles can be detected by photographic film Particles can also be detected (and counted) by a Geiger-Müller tube (GM tube) connected to a counter

Background radiation There are small amounts radioactive particles around us all the time. This is called background radioactivity. The amount varies depending on location.

Background radiation Background radiation comes from Cosmic rays from space Radioactive rocks in the ground Nuclear tests Nuclear bombs Nuclear accidents

Radiation Safety Run away! In other words keep the distance between you and a radioactive source as big as possible! Mr Porter

Radiation Safety Don’t waste time! In other words limit the time you are exposed to radiation.

Radiation Safety If you can’t run away, hide behind something! Put a barrier between you and the radiation source that can absorb the radioactive particles

Today’s lesson 7.4 understand that alpha and beta particles and gamma rays are ionising radiations emitted from unstable nuclei in a random process 7.5 describe the nature of alpha and beta particles and gamma rays and recall that they may be distinguished in terms of penetrating power 7.6 describe the effects on the atomic and mass numbers of a nucleus of the emission of each of the three main types of radiation 7.7 understand how to complete balanced nuclear equations

3 types of particle There are 3 (at least in IGCSE!) types of particles that can be ejected from an unstable nuclei. You’ll learn about some really weird ones in year 13!

Alpha particles α Hi!

Alpha particles 2 protons and 2 neutrons joined together The same as the nucleus of a helium atom Stopped by paper or a few cm of air Highly ionising Deflected by electric and strong magnetic fields He

Alpha Decay U Th α Atomic number goes down by 2 Atomic mass goes down by 4

Beta particles β Yo!

Beta particles Fast moving electrons Stopped by about 3 mm of aluminium Weakly ionising Deflected by electric and magnetic fields e 0

Beta decay In the nucleus a neutron changes into an electron (the beta particle which is ejected) and a proton (which stays in the nucleus) During beta decay the mass number stays the same but the proton number goes up by 1. e 0 Th Pa

Gamma rays Hola!

Gamma rays High frequency electromagnetic radiation Stopped by several cm of lead Very weakly ionising NOT affected by electric or magnetic fields

Gamma rays Associated with alpha decay U Th α

Questions?

1.Revising the properties of the three types of nuclear radiation Alpha, Beta and Gamma 2.The discovery of the nucleus 3.Using nuclear reactions (fission and fusion) to generate electricity Radioactivity - Additional

Alpha radiation is the release of an alpha particle. It occurs in very heavy elements such as Uranium and Radium. An alpha particle is made up of 2 neutrons and two protons so it has an overall charge of +2 and a mass of 4 amu (atomic mass units). The alpha particle does not travel far, so the best way to protect yourself from alpha radiation is just to keep half a meter away from it or use clothing or a face mask. This is easy if the source is a solid block but if it inhaled or ingested it and damage your internal organs. Radium Radon Ra Rn 4242 

A Beta particle is emitted when a neutron in the nucleus changes into a proton releasing a negative charge in the form of a fast moving electron. It has an overall charge of -1 and a negligible mass (about 1/2000 amu) The best way to protect yourself from a beta source is keep few meters away from it or to protect yourself with metal sheets. Polonium  Astatine Po At 0

Gamma After a nucleus has emitted an  -particle or a  -particle, it may still have too much energy: we say it is in an "excited state". It can get rid of this energy by emitting a pulse of very high frequency electromagnetic radiation, called a gamma ray. Gamma rays have no mass and no charge. Gamma is very penetrating and is long range. You need protect yourself with at least 10 cm of lead or to be quite a long way away from a gamma source. Iodine I Iodine I Next: The discovery of the nucleus

The discovery of the nucleus Dalton’s Atomic Theory: Atoms are indestructible and indivisible (cannot be divided into smaller particles). John Dalton ( ) Thomson’s Plum Pudding Model of the Atom: Thompson ( ) Thompson discovered the ‘electron’. So Dalton’s model of the atom was no longer acceptable because now there is something inside the atom. Thomson believed the atom was made of positively charged matter with negatively charged electrons scattered throughout like plums in a plum pudding (or chocolate chips in chocolate chip cookie).

Ernest Rutherford ( ) wanted to test Thompson’s plum pudding model of the atom using his newly discovered alpha particles. He carried out the ‘gold foil experiment in 1910: He bombarded thin gold foil with a beam of ‘alpha’ particles. He expected it to be just like firing bullets at a tissue paper. “If the positive charge was evenly spread out like Thompson says, the beam should have easily passed through”.

Rutherford experiment Expected Found Conclusion: All of the positive charge, and most of the mass of an atom are concentrated in a small core, called the nucleus. Next: fission and fusion

Energy from the Nucleus Nuclear FissionNuclear Fusion Nuclear fission occurs when a Uranium-235 nucleus or a Plutonium-239 nucleus splits. Nuclear fusion occurs when two small nuclei are forced close enough together so they join to make large nucleus.

Energy from the Nucleus Nuclear FissionNuclear Fusion Nuclear fission occurs when a Uranium-235 nucleus or a Plutonium-239 nucleus splits. Nuclear fusion occurs when two small nuclei are forced close enough together so they join to make large nucleus.

Energy from the Nucleus Nuclear FissionNuclear Fusion Nuclear fission occurs when a Uranium-235 nucleus or a Plutonium-239 nucleus splits. Nuclear fusion occurs when two small nuclei are forced close enough together so they join to make large nucleus. When a nucleus undergoes fission, it releases two or three neutrons which go on to cause further fission resulting in a chain reaction.

Energy from the Nucleus Nuclear FissionNuclear Fusion Nuclear fission occurs when a Uranium-235 nucleus or a Plutonium-239 nucleus splits. Nuclear fusion occurs when two small nuclei are forced close enough together so they join to make large nucleus. When a nucleus undergoes fission, it releases two or three neutrons which go on to cause further fission resulting in a chain reaction. The energy released could be used to generate electricity.

Energy from the Nucleus Nuclear FissionNuclear Fusion Nuclear fission occurs when a Uranium-235 nucleus or a Plutonium-239 nucleus splits. Nuclear fusion occurs when two small nuclei are forced close enough together so they join to make large nucleus. When a nucleus undergoes fission, it releases two or three neutrons which go on to cause further fission resulting in a chain reaction. The energy released could be used to generate electricity. the waste product is highly radioactive substances (Barium and Krypton) which need to be disposed of safely.

Energy from the Nucleus Nuclear FissionNuclear Fusion Nuclear fission occurs when a Uranium-235 nucleus or a Plutonium-239 nucleus splits. Nuclear fusion occurs when two small nuclei are forced close enough together so they join to make large nucleus. When a nucleus undergoes fission, it releases two or three neutrons which go on to cause further fission resulting in a chain reaction. Nuclear fusion is the process by which energy is released in the Sun. Energy is released when two nuclei are fused together. The energy released could be used to generate electricity. the waste product is highly radioactive substances (Barium and Krypton) which need to be disposed of safely.

Energy from the Nucleus Nuclear FissionNuclear Fusion Nuclear fission occurs when a Uranium-235 nucleus or a Plutonium-239 nucleus splits. Nuclear fusion occurs when two small nuclei are forced close enough together so they join to make large nucleus. When a nucleus undergoes fission, it releases two or three neutrons which go on to cause further fission resulting in a chain reaction. Nuclear fusion is the process by which energy is released in the Sun. Energy is released when two nuclei are fused together. The energy released could be used to generate electricity. the waste product is highly radioactive substances (Barium and Krypton) which need to be disposed of safely.

Energy from the Nucleus Nuclear FissionNuclear Fusion Nuclear fission occurs when a Uranium-235 nucleus or a Plutonium-239 nucleus splits. Nuclear fusion occurs when two small nuclei are forced close enough together so they join to make large nucleus. When a nucleus undergoes fission, it releases two or three neutrons which go on to cause further fission resulting in a chain reaction. Nuclear fusion is the process by which energy is released in the Sun. Energy is released when two nuclei are fused together. The energy released could be used to generate electricity. the waste product is highly radioactive substances (Barium and Krypton) which need to be disposed of safely. The waste product is Helium which is a harmless gas. On the other hand it has technical difficulties as a very high temperatures are needed to start the fusion of nuclei.

Nuclear Fusion

NUCLEAR FUSION Whereas nuclear FISSION involves very large nuclei splitting into smaller nuclei, FUSION involves the SMALL nuclei JOINING TOGETHER to form larger ones. FUSION powers STARS and is the method by which all of the ELEMENTS in the Universe were formed from the original simple particles present after the BIG BANG

In stars, the 3 isotopes of HYDROGEN are often involved in fusion n 0 1 neutron H 1 1 p 1 1 proton H 1 2 deuterium H 1 3 tritium Conditions needed for a fusion reaction If the TEMPERATURE is not high enough, the particles will simply collide and ‘rebound’ due to electrostatic repulsion

2 protons positron (neutrino) deuterium If the temperature is high enough, the particles have enough kinetic energy to overcome their repulsion and FUSE (the neutrino is a tiny neutral particle always created with a positron – antineutrinos are created with electrons) H 1 1 H e ν 0 0 Temperatures of MILLIONS OF DEGREES are needed to start the reaction. As with fission, the products have slightly less mass than the reactants with the ‘missing’ mass being converted to energy

In the core of a star, many fusion reactions are taking place at the same time Gigantic amounts of energy are released.

As a star’s life cycle goes on, fusion in the core produces heavier and heavier elements. The process continues until IRON (26 protons) is produced. Nucleosynthesis means the creation of new heavier nuclei from lighter ones

Older stars build up layers of heavier and heavier elements. Eventually, fusion in the core stops and gravity suddenly collapses the star. The collapse produces a devastating SUPERNOVA explosion. In a supernova the conditions are so extreme that nuclei fuse to produce all of the elements heavier than iron which are then blasted into space, later to form new stars and planets Elements up to iron iron to uranium

Heavier elements from a dead star are thrown out by the supernova into space as gas and dust New stars and planets form from the gas and dust NEWLY CREATED ELEMENTS ARE RECYCLED

CAN NUCLEAR FUSION FILL THE ENERGY SUPPLY GAP BACK HERE ON EARTH? Fossil fuels SUPPLIES RUNNING OUT, POLLUTION Nuclear fission SAFETY CONCERNS, WASTE PROBLEM Renewables NOT ENOUGH ENERGY PRODUCED

We already rely on a nuclear fusion reactor 150 million km away for virtually all of our energy, whether directly through solar heating or indirectly through wind, hydro, food and fossil fuels. Is it possible to create a little piece of the Sun here on Earth? Many scientists say that if we could successfully control nuclear fusion, we could produce, cleanly, more energy than we could ever need

FUSION POWER STATIONS? Compared to nuclear FISSION, nuclear FUSION reactions: release EVEN MORE energy per kg of fuel make less radioactive emissions as many of the products are stable (eg He-4) use ‘cleaner’ fuel: isotopes of hydrogen, which can be made from water and lithium The most promising reaction for man made fusion power is the fusion of deuterium and tritium ( 2 H and 3 H). However, there are MAJOR practical problems for scientists and engineers to overcome

To start a fusion reaction the fuel must be heated to a temperature about 150 million degrees. This makes it into a PLASMA – a gas in which the electrons have been stripped from the nuclei. FUSION IN A REACTOR?

PLASMAS: Flame, Plasma Ball, Ball Lightning The main problems are: How can the plasma be heated to such extreme temperatures? What can it be kept in? Any physical container would simply vaporise. Consider: The plasma is a gas. Its particles need to be supplied with more kinetic energy to raise the temperature. The plasma is a gas made of IONS, which will make an electric current when they move. Electric currents can be deflected by magnetism.

The plasma can be heated: By the electric current that flows when a magnetic field is applied to the ions By injecting extra hydrogen atoms with high kinetic energy By beaming in microwaves HEATING THE PLASMA

MAGNETIC PLASMA CONFINEMENT In a star, the plasma is confined by GRAVITY. In a fusion reactor, the plasma is confined using MAGNETIC FIELDS The + ions and electrons in the plasma move in spirals around the magnetic field lines

Very powerful magnetic fields are used to confine the plasma into a TOROID (doughnut) shape. This allows it to be heated to the 150 million °C needed without touching the chamber walls

Inside the JET (Joint European Torus) experimental fusion reactor at Culham in Berkshire

Powering up the JET The hot plasma is visible through an observation window. The reactor never contains more than a few grams of plasma at once.

European researchers are experimenting with a spherical, rather than toroidal plasma

Laser Ignition Fusion “Inertial Confinement” Researchers in the US are trialling a different system using small pellets of hydrogen fuel in lithium cases. Intensely powerful LASERS are focussed on the pellets, starting a fusion reaction. These are in effect tiny nuclear fusion bombs. A continuous series of pellets would be detonated, with the heat produced being used to produce electricity

Fusion power stations could provide the very large amounts of continuous energy without producing any greenhouse gases The fuel supply is almost inexhaustible: deuterium is extracted from seawater tritium is made in the reactor from lithium which is very common in the Earth’s crust H 1 2 H 1 3 The lithium from one laptop battery, combined with the deuterium in 100 litres of water, can cover the electricity use of an average European citizen for 30 years. Energy and Fuel Supply Issues

Radiation and Safety Deuterium ( 2 H) and 4 He are stable Whilst tritium is radioactive, it only emits low energy beta particles with a short half life (12 yr). The reaction emits neutrons which are absorbed by the reactor vessel walls, making them weakly radioactive. By choosing suitable metals for the reactor walls, the half lives of the radioactive isotopes produced by the neutrons are around 10 years, so there is no long term waste issue as there is for fission.

Radiation and Safety The mass of fuel in the reactor is no more than a few grams at a time. If the fusion process is disrupted by for example: cutting the fuel supply interrupting the heating mechanisms damage to the reactor walls …the reaction stops immediately

After about 40 years research and billions of dollars of funding….. JET / ITER / TOKAMAK Magnetic confinement

NIF Laser Ignition …continuous controlled fusion in a reactor has still not been achieved.