Transcript radiation!!! - Mr Schmitt

Define and understand the following terms
 Radioactivity
 Repulsive Force
 Nuclear Force
 Isotope
 Be able to describe/explain why some atoms are
radioactive
 Be able to describe and balance
 Positive alpha radiation α equations
 Negative beta radiation β equations
 Neutral gamma radiation γ equations


Natural background radiation exists all
around us.
 This radiation consists of high energy particles or
waves being emitted from a variety of materials.
▪ Like the sun, radio stations, electronic devices, TV’s, cell
phones, lights, etc...

Being exposed to radioactive materials can
be beneficial or harmful




Light!
X-rays
Radiation therapy (cancer treatment)
Electricity generation (nuclear power plants)

Too much of any radiation...
 Can cause Cancer
▪ Skin cancer from sun (UV) radiation
▪ Body cancer from high amounts of radiation
 Can cause genetic mutations
▪ Radiation affects and mutates the DNA in our body cells
and then causes mutations in offspring

Radioactivity (radiation) is the release of
high energy particles or waves from
unstable nuclei
 When atoms lose high energy particles and waves,
ions or even new atoms can be formed
 High energy waves and particles are called
‘radiation’ when they leave the atom



Note: Radioactive = Unstable
Recall the structure of an atom.
What lives in the nucleus?
REPULSIVE
FORCE
 Protons
 Neutrons
P+
N
P+
P+
NUCLEAR
FORCE
N
N
P+
N
P+
N





The nucleus is full of positive protons
Like charges want to repel= REPULSIVE
FORCE
Fortunately the neutrons are there to help
hold the nucleus together= NUCLEAR FORCE
Sometimes there are not enough neutrons in
the nucleus.
This means the balance between repulsive
forces and nuclear forces is off!

When the forces do not balance, the nucleus
will make adjustments by kicking out
particles or energy out of their nucleus.

This is called RADIATION

The higher the frequency of radiation
(ie. the shorter the wavelength) = The more
harmful the radiation is for you!

Radiation is everywhere, but can be difficult to
detect
 Roentgen named X-rays with an “X” 100 years ago
because they were previously unknown
 Becquerel realized uranium emitted seemingly
invisible energy as well
 Marie Curie and her husband Pierre named this
energy radioactivity
▪ Early discoveries of radiation relied on photographic
equipment
▪ Later, more sophisticated devices such as the Geiger counter
were developed to more precisely measure radioactivity

Isotopes are different atoms of the same
element, with the difference between the two
atoms being the number of neutrons in the
nucleus, the number of protons is the same.
 Isotopes have the same number of protons and
therefore the same atomic number as each other.
 By having different numbers of neutrons, isotopes
have different mass numbers.

Isotopes are written using standard atomic notation.
 Chemical symbol, atomic number & mass number.
 Potassium has three isotopes

39
19
K,
40
19
K,
41
19
K
Periodic Table
Nuclear Symbol
MASS
ATOMIC #
CHEMISTS
PHYSICISTS

It is now much easier because of the
physicists
14
6
8
MASS
C
12
ATOMIC #
6
# Neutrons
6
C
Practice!


Work with a partner to do the practice
problems on page 291 in your notebook.
(Don’t write in your textbooks!!!)
Check your answers on page 592

Unlike all previously discovered chemical
reactions, radioactivity sometimes resulted in
the formation of completely new atoms.
 Radioactivity results from an atom having an unstable
nucleus
 When these nuclei lose energy and break apart, decay
occurs
▪ Radioactive decay releases energy from the nucleus as
radiation
▪ Radioactive atoms release energy until they become stable,
often ending up as different atoms
▪ For example: uranium-238 (parent nucleus) decays in several stages
until it finally becomes lead-206 (daughter nucleus)
▪ An element may have only certain isotopes that are
radioactive. These are called radioisotopes. Carbon-13 is an
example.
When atoms are unstable, they break apart
to become new, more stable atoms and
release radiation... There are 3 types that can
be released.
1. Positive alpha radiation α
2. Negative beta radiation β
3. Neutral gamma radiation γ


Alpha radiation is a stream of alpha particles
 These particles are the same as a helium nucleus
4
so we represent α radiation as: 4
2
2
 Because it has two protons, it has a charge of 2+
 or He
 The release of alpha particles is called alpha decay
 Alpha particles are slow and penetrate materials
much less than the other forms of radiation.
▪ A sheet of paper will stop an alpha particle
Decays to
+
** Notice – the product side atomic masses
add up to the reactant side (as well as the
atomic numbers)
You try:
225
89
____
Ac 
____
221
87
Fr +
4
2
He

Beta radiation is a stream of beta particles
 Beta particles are the same as an electron. So we
represent radiation as:
0
-1
 or e
0
-1
 Beta decay occurs when a neutron changes into a
proton + an electron. The proton stays in the
nucleus and the electron is released.
 Beta particles are faster than alpha particles. A
sheet of aluminum foil will stop a beta particle.
Decays to
+
** Notice – the product side atomic masses
add up to the reactant side (as well as the
atomic numbers)
You try:
___
201
80
Hg 
201
81
____
Tl +
0
-1
β
O
-1

Gamma radiation is a ray of high energy, shortwavelength radiation
 no charge and no mass
 the highest energy form of electromagnetic radiation
 Occurs when nucleus is in excited state (shown by by
*) after emitting an alpha or beta particle, and needs
to release more energy. It is shown by: 0

0
 It takes thick blocks of lead or concrete to stop
gamma rays
 Sometimes reactions can release more than 1 type of
radiation.
▪ For example: Uranium-238 decays into an alpha particle and
also releases gamma rays
238
92

U 
Th + He + 2
4
2
Uranium is releasing an Alpha particle and
Gamma Radiation
60
28

234
90
Ni* 
60
28
Ni + 
0
0
Nickel is decaying and giving off just Gamma
Radiation
 Notice – no change in atomic mass or number!
231
91
/ He
Pa  ____
___
89 Ac + 2α
227
____
C  ____
N + -1β
7 ___
14
____
14
6
4
235
0
Rb + 0γ
U  55Cs + ____
37 ____
92
143
92
____
0

Try practice problems on page 295 and 296.
Check your answers.