Transcript Nuclear_Decay - Port Hope High School

Mass-Energy Equivalence
All matter is a form of stored energy.
Mass-Energy Equivalence
All matter is a form of stored energy.
If matter of mass m is converted to
energy, the amount of energy E that can
be released is equal to:
Mass-Energy Equivalence
All matter is a form of stored energy.
If matter of mass m is converted to
energy, the amount of energy E that can
be released is equal to:
E = mc2
Mass-Energy Equivalence
All matter is a form of stored energy.
If matter of mass m is converted to
energy, the amount of energy E that can
be released is equal to:
E = mc2
c = 3.0 x 108 m/s
Mass-Energy Equivalence:
Example
What is the energy equivalent of a 52 kg
person?
Mass-Energy Equivalence:
Example
What is the energy equivalent of a 52 kg
person?
m  52 kg
c  3.0 108
E ?
m
s
Mass-Energy Equivalence:
Example
What is the energy equivalent of a 52 kg
person?
m  52 kg
c  3.0 108
E ?
E  mc 2
m
s

E  52 kg  3.0 10
E  4.7  10 J
18

8 m 2
s
The Mass Defect
More practically, we look at the energy
equivalent of the mass defect.
The Mass Defect
More practically, we look at the energy
equivalent of the mass defect.
The Mass Defect
Consider a Carbon 12 nucleus:
The Mass Defect
Consider a Carbon 12 nucleus:
6 protons, 1.007276 amu each
+ 6 neutrons, 1.008665 amu each
= 12.095646 amu
The Mass Defect
Consider a Carbon 12 nucleus:
6 protons, 1.007276 amu each
+ 6 neutrons, 1.008665 amu each
= 12.095646 amu
Actual mass of Carbon 12 nucleus:
= 11.996709 amu
The Mass Defect
The 0.098937 amu mass defect is the
binding energy of the nucleus.
E = mc2
E ≈ (0.098937)(1.66 x 10-27 kg)(3.0 x 108 m/s)2
E ≈ 1.5 x 10-11 J
Nuclear Decay
•
•
•
•
•
Alpha Decay
Beta Decay
Gamma Decay
Positron Emission
Electron Capture
Discovery of Radioactivity
• Radioactivity is the release of energy or
particles when an atom disintegrates (demo)
• Radioactivity was discovered when minerals
were exposed to film through an opaque cover
• The 3 types of radioactivity can be shown by
passing emissions through an electrical field:
Lead block
+
Radioactive
substance


–

Phosphorescent
zinc sulfide
detection screen
Strong magnetic or
electrostatic field
Types of Radioactivity
Types of radiation: 1) , 2) , 3) 
1. Alpha () particles are symbolized as 42He
2. Beta () particles (essentially electrons) are 0–1e
3. Gamma () rays are symbolized as 00
• You can determine the composition of each:
: mass of 4 u, charge of +2 (2 p+, 2 n0, 0 e–)
• Other symbols: proton = 11p, neutron = 10n
• There are different terms to describe the
different types of nuclear reactions
• “alpha decay” means an  particle is given off.
• Other: beta decay, fusion (meaning to bring
together), fission (meaning to break apart)
Alpha Decay
Alpha decay occurs when a helium nucleus is
emitted from the nucleus of an unstable
atom, forming a new atom with a smaller
mass.
When an atom undergoes alpha decay,
the atomic number of the atom
decreases by two and the atomic mass
decreases by four.
234
90
Th 
Ra  He
230
88
4
2
Alpha Decay
In alpha decay/emission, a helium nucleus is
emitted.
Alpha Emission
In alpha emission, a helium nucleus is
emitted.
240
94
Pu  U  He
236
92
4
2
This reaction can be represented by an
equation.
Alpha Emission
In alpha emission, a helium nucleus is
emitted.
240
94
parent
nucleus
Pu  U  He
236
92
daughter
nucleus
4
2
alpha particle
Alpha Emission
In alpha emission, a helium nucleus is
emitted.
mass
number
240
94
atomic number
Pu  U  He
236
92
4
2
Beta Decay
Beta decay is when an electron (called in this
context a “beta particle”) is emitted from
the nucleus of an atom, while a neutron turns
into a proton.
As a result, the atomic number of the
element increases by one, while the
mass stays the same.
O F  e
18
8
18
9
0
-1
Gamma Decay
Gamma decay is when very high energy light
called gamma rays are emitted from a nucleus
to bring it to a lower energy state.
Gamma decay generally takes place at
the same time as other nuclear
reactions.
U  He 
238
92
4
2
Th  
234
90
0
0
Positron Emission
Positrons are the antimatter equivalent
to electrons, so they have the same
mass but a charge of +1.
Positron emission is when a positron is
given off by a nucleus.
Positron emission causes the atomic
number of the element to decrease but
the atomic mass to stay the same.
Na Ne e
22
11
22
10
0
1
Electron Capture
Electron capture is when an electron is
absorbed by the nucleus of an atom,
causing the atomic number to decrease
by one but the atomic mass stays the
same.
Hg  e 
201
80
0
-1
Au
201
79
Nuclear equations
Q. Write the beta
decay for C-14
14
6C
Q. Write the alpha 209
84
decay for 209Po

0
-1 e
Po 
+
14
7N
4
205
2 He + 82 Pb
Q. Complete this fission reaction
235
1
1
139
94
+
0 n  3 0 n + 56 Ba + 36 Kr
92 U
In all cases, charge and mass must be balanced