Transcript Lesson 1 Atomic structure background

Do now!
Can you write the
title
Radioactivity
in your books?
Don’t forget you have a
test on Thursday!
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 GeigerMuller 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)
7
6
3
3
Li
Li
Isotopes
For example, Lithium atoms occur in two forms,
Lithium-6 and Lithium-7
4 neutrons
3 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!
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
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.
Let’s try some
questions.