Do now!
Can you write the title
P15 Radioactivityin your books?
Radioactivity
Today’s lesson
• Demonstrate understanding of background radiation.• Describe the detection of α-particles, β-particles and γ-
rays.• State that radioactive emissions occur randomly over
space and time.• State the meaning of radioactive decay.• Describe the hazards of ionising radiation to living things.• Describe how radioactive materials are handled, used
and stored in a safe way to minimise the effects of these hazards.
• Use the term isotope.
The atom
orbiting 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
orbiting electrons
Nucleus (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
4 neutrons3 neutrons
Relative atomic mass
On 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 p251Element 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.
We say the atom has decayed
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!
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
COPY PLEASE
Hazards of ionising radiation
Ionising
• The radioactive particles (more about later) can ionise atoms they collide with
Hazards of ionising radiation
• Ionizing radiation has the ability to break chemical bonds and facilitate exotic chemical reactions within living cells. The damage caused to cells can vary;
• radiation burns• hair loss (temporary or permanent)• cancer• reproductive sterility• mutations in offspring
Radiation Safety
Radiation Safety
• Run away!
Mr Porter a few years ago
Get away dog!
Radiation Safety
• Run away!• In other words keep the distance between
you and a radioactive source as big as possible!
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
Radiation safety
• Keep the distance between you and a radioactive source as big as possible (use tongs etc.)
• Limit the time you are exposed to radiation.
• Put a barrier between you and the radiation source that can absorb the radioactive particles (normally lead)
Let’s try some questions.
Let’s do some reading. Page 250 onwards.