Radiation
What is it?
Where does it come from?
Radiation discovered
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Henri Becquerel discovered an
invisible, penetrating radiation
emitted spontaneously by Uranium.
Pierre and Marie Curie discovered
two other elements that emitted
similar radiations. Polonium and
Radium. Called the phenomenon
"radioactivity".
Now defined as the emission of
electromagnetic radiation and/or
particles from unstable nuclei
So, it is the unstable
nucleus of an atom
falling apart
The bigger the nucleus, the greater
the chance it will fall apart, which
brings us to nuclear chemistry
Nuclear Stability
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Not all combinations of protons and
neutrons are stable.
To determine stability N/Z is examined,
where N = neutrons and Z = protons.
For small atomic numbers, the atom is
stable if N/Z=1
For larger atomic numbers, the atom is
stable if N/Z is closer to 1.5
Page 646
Figure 6
no
Yellow area
is stable.
yes
Mass number
no
yes
Protons
Have to subtract to
get neutrons
Are these
stable?
13 139
C
Ba
6
56
40 133
P
Sn
15 50
So, since some nuclei are
unstable, they will fall apart
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This leads to radioactive decay
Radioactivity – the process by which an
unstable nucleus emits one or more
particles or energy in the form of
electromagnetic radiation
By emitting particles and/or energy, the
nucleus can stabilize itself
Four main types of
radiation

Alpha radiation- does not penetrate the
skin, emits positive charge (Helium
nucleus), weakest type of radiation

Beta radiation -penetrates the skin, emits
negative charge(fast moving electron)

Positron – penetrates the skin, it is the
antiparticle of the electron

Gamma radiation- emits high energy,
penetrates the skin fully
Table 1 – Page 648
These particles can either
be captured or emitted
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If they are absorbed by the reactants,
they are captured
In other words, if they appear on the
left side of the equation
If they are given off the reactants,
they are emitted
In other words, if they appear on the
right side of the equation
Take a look at the following examples
Beta Particle Emission
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If N/Z is too large, a neutron may emit
a high level electron and turn into a
proton.
Question: What happens if the number
of protons change?
Answer: The atom changes to a new
element.
Note: If you treat
14
14
0
Example: 6 C  7 N + -1 e  as an = sign,
numbers should
equal
Electron Capture
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If N/Z is too small, a proton may
absorb a high level electron and turn
into a neutron.
Once again, the element will change
51
0
51
Example: 24 Cr + -1 e  23 V + 
Note that in this case, extra energy is
released. This energy is released as
gamma rays
Positron Emission
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If N/Z is too small, a proton may release
a positron, (antiparticle of an electron)
and turn into a neutron.
Once again, the element will change
49
49
0
Example: 24 Cr  23 V + +1 e
If a positron meets an electron, all the
mass will be annihilated and is converted
to energy (gamma rays)
Positron + electron = 2 gamma rays
Alpha Particle Emission
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If N/Z is much larger than 1, then a
nucleus can stabilize itself by emitting an
alpha particle (Helium Nucleus).
Example: 238 U  234 Th + 4 He
92
90
2
Note again, that every nuclear equation
must be balanced.
Top number on right must equal top
numbers on left and bottom numbers on
right must equal the bottom number on
left
Examples
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Write a balanced equation for each
nuclear equation
218
214
4
Alpha emitted
Po

+
Pb
He
84
82
2
142

61
Pm +
253

99
Es +
0
e
1
142
 60 Nd
1
Beta captured
256
He  0 n + Md Alpha captured
101