Don’t forget you have a test on Thursday! Do now! Don’t forget you have a test on Thursday! Can you write the title Radioactivity in your books?

Radioactivity

Today’s 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 Atomic mass (mass number) = number of protons and neutrons 7 Li 3 Atomic number (proton number) = number of protons

Isotopes 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 7 Li 3 6

Isotopes For example, Lithium atoms occur in two forms, Lithium-6 and Lithium-7 3 neutrons 4 neutrons Li 3 7 Li 3 6

Li Relative atomic mass 6.941 3 On average, lithium atoms have a mass of 6.941 (relative to Carbon 12) 6.941 Li 3

Hola! Mi nombre es tritium y yo soy de Madrid! Isotopes of Hydrogen The three isotopes of Hydrogen even have their own names! Hola! Mi nombre es tritium y yo soy de Madrid! Hi! I’m hydrogen They call me deuterium H 1 H 1 2 H 1 3

Questions! Element Chemical symbol Atomic number Hydrogen H 1 Helium 2 Lithium Li 3 Beryllium Be 4 Boron B 5 Carbon C 6 Nitrogen N 7 Oxygen O 8 Radium Ra 88 Thorium Th 90 Uranium U 92 Plutonium Pu 94

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

Radiation Safety Run away! Mr Porter

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!

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!

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

Let’s try some questions.