Do now! Can you write the title Radioactivity in your books?
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Transcript of Do now! Can you write the title Radioactivity in your books?
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Do now!
Can you write the title
Radioactivityin your books?
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Radioactivity
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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
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The atom
orbiting electrons
Nucleus (protons and neutrons)
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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)
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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
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Relative atomic mass
On average, lithium atoms have a mass of 6.941 (relative to Carbon 12)
Li3
6.941
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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!
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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
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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.
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Unstable nuclei
To become stable, an unstable nuclei emits a particle.
We say the atom has decayed
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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!
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Becquerels (Bq)
• The amount of radioactivity given out by a substance is measured in Becquerels. One becquerel is one particle emitted per second.
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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
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Background radiation
There are small amounts radioactive particles around us all the time. This is called background radioactivity. The amount varies depending on location.
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Background radiation
Background radiation comes from
• Cosmic rays from space
• Radioactive rocks in the ground
• Nuclear tests• Nuclear bombs• Nuclear accidents
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Radiation Safety
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Radiation Safety
• Run away!• In other words keep the distance between
you and a radioactive source as big as possible!
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Radiation Safety
• Don’t waste time!
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Radiation Safety
• Don’t waste time!• In other words limit the time you are exposed
to radiation.
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Radiation Safety
• If you can’t run away, hide behind something!
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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
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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)
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Let’s try some questions.