Transcript Lesson 1 Atomic structure background and

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title
P15 Radioactivity
in your books?
Radioactivity
Today’s lesson
• Demonstrate understanding of background radiation.
• Describe the detection of α-particles, β-particles and γrays.
• 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
Atomic mass (mass number)
= number of protons and
neutrons
7
orbiting
electrons
Li
3
Atomic number (proton number)
= number of protons
Nucleus (protons
and neutrons)
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)
3 neutrons
4 neutrons
7
6
3
3
Li
Li
Relative atomic mass
On average, lithium atoms have a mass of 6.941
(relative to Carbon 12)
6.941
3
Li
Isotopes of Hydrogen
The three isotopes of Hydrogen even have their
own names!
Hi! I’m
hydrogen
Hola! Mi
nombre es
tritium y yo
soy de
Madrid!
They call
me
deuterium
1
2
3
1
1
1
H
H
H
Questions p251
Element
Chemical
symbol
Atomic
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
COPY PLEASE
•
•
•
•
•
Background radiation
comes from
Cosmic rays from
space
Radioactive rocks in
the ground
Nuclear tests
Nuclear bombs
Nuclear accidents
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!
Get away dog!
Mr
Porter
a few
years
ago
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.