don’t forget you have a test on thursday!
DESCRIPTION
RadioactivityTRANSCRIPT
Do now! Don’t forget you have a test on Thursday!
Can you write the title
Radioactivityin 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 atomorbiting electrons
Nucleus (protons and neutrons)
Nuclide notation
Li3
7
Atomic number (proton number) = number of protons
Atomic mass (mass number) = number of protons and neutrons
Isotopes
Li3
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)
Li3
6
Isotopes
Li3
7
For example, Lithium atoms occur in two forms, Lithium-6 and Lithium-7
Li3
6
4 neutrons3 neutrons
Relative atomic massOn average, lithium atoms have a mass of 6.941 (relative to Carbon 12)
Li3
6.941
Isotopes of Hydrogen
H1
1
The three isotopes of Hydrogen even have their own names!
H1
2
H1
3
Hi! I’m hydrogen
They call me
deuterium
Hola! Mi nombre es tritium y yo
soy de Madrid!
Questions!Element Chemical
symbolAtomic number
Hydrogen H 1
Helium He 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 nucleiThe 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.
Let’s try some questions.