The Hindenburg Disaster1937

MAJOR DISASTERS

The Titanic 1912

Tacoma bridge

1940

Twin Towers 2001

Hiroshima and Nagasaki1945

Two atomic bombs:

6th Aug 1945 :

Little Boy Hiroshima

9th Aug 1945 :Fat Man Nagasaki

Nuclear Reactions

Fission and FusionGEE KUANG BENG

SMK METHODIST (ACS)

Form 5 Physics

Little Boy – Atom Bomb – Hiroshima 6 Aug 1945

CS 5.4

Understanding nuclear energy

You should be able to define atomic mass unit (a.m.u)describe and give examples of nuclear fissiondescribe Chain reactionsdescribe and give examples of nuclear fussionrelate release of nuclear energy to the equation E=mc2

describe generation of electricity from nuclear fission

PHEW!

Fission

When atoms are bombarded with neutrons, their nuclei splits into 2 parts which are roughly equal in size.

Nuclear fission in the process whereby a nucleus, with a high mass number, splits into 2 nuclei which have roughly equal smaller mass numbers.

During nuclear fission, neutrons are released.

U23592n

1 0

The Fission Process

A neutron travels at high speed towards a uranium-235 nucleus.

U23592n

1 0

The neutron strikes the nucleus which then captures the neutron.

The Fission Process

U23692

The nucleus changes from being uranium-235 to uranium-236 as it has captured a neutron.

The Fission Process

The uranium-236 nucleus formed is very unstable.

The Fission Process

It transforms into an elongated shape for a short time.

The uranium-236 nucleus formed is very unstable.

The Fission Process

It transforms into an elongated shape for a short time.

The uranium-236 nucleus formed is very unstable.

The Fission Process

It transforms into an elongated shape for a short time.

It then splits into 2 fission fragments and releases neutrons.

The Fission Process

14156Ba

9236Kr

n 1 0

n 1 0

n 1 0

It then splits into 2 fission fragments and releases neutrons.

The Fission Process

14156Ba

9236Kr

n 1 0

n 1 0

n 1 0

It then splits into 2 fission fragments and releases neutrons.

The Fission Process

14156Ba

9236Kr

n 1 0

n 1 0

n 1 0

It then splits into 2 fission fragments and releases neutrons.

The Fission Process

14156Ba

9236Kr

n 1 0

n 1 0

n 1 0

Nuclear Fission

1n + 235U -> 91Kr + 142Ba + 31n

Nuclear Fission Examples

U235

92 +Ba141

56+ n1

03n

1

0 +Kr 92

36

U235

92 +Cs138

55+ n1

02n

1

0 +Rb 96

37

Energy Released

The energy released can be calculated using the equation:

E = mc2

Where:

E = energy released (J)

m = mass difference (kg)

c = speed of light in a vacuum (3 x 108 ms-1)

E

m c2

Mass-Energy Relationship

• Einstein’s famous equation E = mc2

• A nucleus is measured to have less mass than the sum of its parts

• 12C has a mass exactly 12.00000 amu• Six protons have mass 6 x 1.00728 amu• Six neutrons have mass 6 x 1.00867 amu• Parts have mass 12.09570 amu

Mass-Energy Relationship

• So, where does the mass go?• It is the binding energy that is holding the

nucleus together• Interesting to look at the mass per nucleon

as we change the atomic number (change which element we look at)

Energy from Fission

U235

92 +Cs138

55+ n1

02n

1

0 +Rb 96

37

Element Atomic Mass (kg)

23592U 3.9014 x 10-25

13855Cs 2.2895 x 10-25

9637Rb 1.5925 x 10-25

10n 1.6750 x 10-27

Energy from Fission

Calculate the total mass before and after fission takes place.

The total mass before fission (LHS of the equation):

The total mass after fission (RHS of the equation):

3.9014 x 10-25 + 1.6750 x 10-27 =

2.2895 x 10-25 + 1.5925 x 10-25 + (2 x 1.6750 x 10-27) =

3.91815 x 10-25 kg

3.9155 x 10-25 kg

Energy from Fission

The total mass before fission =

The total mass after fission =

3.91815 x 10-25 kg

3.91550 x 10-25 kg

total mass before fission > total mass after fission

Energy from Fission

mass difference, m = total mass before fission – total mass after fission

m = 3.91815 x 10-25 – 3.91550 x 10-25

m = 2.65 x 10-28 kg

This reduction in mass results in the release of energy.

Energy from Fission

E = mc2

U235

92 +Cs138

55+ n1

02n1

0 +Rb 96

37

Calculate the energy released from the following fission reaction:

m = 2.65 x 10-28 kg c = 3 x 108 ms-1

E = E

E = 2.65 x 10-28 x (3 x 108)2

E = 2.385 x 10-11 J

Energy from Fission

The energy released from this fission reaction does not seem a lot.

This is because it is produced from the fission of a single nucleus.

Large amounts of energy are released when a large number of nuclei undergo fission reactions.

Energy from Fission

Each uranium-235 atom has a mass of 3.9014 x 10-25 kg.

The total number of atoms in 1 kg of uranium-235 can be found as follows:

No. of atoms in 1 kg of uranium-235 = 1/3.9014 x 10-25

No. of atoms in 1 kg of uranium-235 = 2.56 x 1024 atoms

Energy from Fission

If one uranium-235 atom undergoes a fission reaction and releases 2.385 x 10-11 J of energy, then the amount of energy released by 1 kg of uranium-235 can be calculated as follows:

total energy = energy per fission x number of atoms

total energy = 2.385 x 10-11 x 2.56 x 1024

total energy = 6.1056 x 1013 J

Chain Reaction

Nuclear fission starts a chain reaction

Chain Reaction

• The key to keeping the reaction going is that at least one of the neutrons given off, must cause another fission

• Controlled reaction in a nuclear reactor• If two or three cause fissions, you can get a

bomb!• Idea of critical mass

Critical Mass

Atom Bomb

Nuclear Reactor

Figure 19.6: Diagram of a nuclear power plant.

Nuclear Fusion

In nuclear fusion, two nuclei with low mass numbers combine to produce a single nucleus with a higher mass number.

H 2

1 +He 4

2+ n1

0H

3

1 +Energy

The Fusion Process

H 2 1

H 3 1

The Fusion Process

H 2 1

H 3 1

The Fusion Process

H 2 1

H 3 1

The Fusion Process

H 2 1

H 3 1

The Fusion Process

The Fusion Process

The Fusion Process

The Fusion Process

The Fusion Process

He 4 2

n 1 0

ENERGY

The Fusion Process

He 4 2

n 1 0

ENERGY

The Fusion Process

He 4 2

n 1 0

ENERGY

The Fusion Process

He 4 2

n 1 0

ENERGY

Energy from Fusion

Element Atomic Mass (kg)

21H 3.345 x 10-27

31H 5.008 x 10-27

42He 6.647 x 10-27

10n 1.6750 x 10-27

H 2

1 +He 4

2+ n1

0H

3

1 +Energy

Energy from Fusion

Calculate the following:

• The mass difference.

• The energy released per fusion.

Energy from Fusion

The total mass before fusion (LHS of the equation):

The total mass after fission (RHS of the equation):

3.345 x 10-27 + 5.008 x 10-27 = 8.353 x 10-27 kg

6.647 x 10-27 + 1.675 x 10-27 = 8.322 x 10-27 kg

H 2

1 +He 4

2+ n1

0H

3

1 +Energy

Energy from Fusion

m = total mass before fission – total mass after fission

m = 8.353 x 10-27 – 8.322 x 10-27

m = 3.1 x 10-29 kg

Energy from Fusion

E = mc2m = 3.1 x 10-29 kg c = 3 x 108 ms-1

E = E

E = 3.1 x 10-29 x (3 x 108)2

E = 2.79 x 10-12 J

H 2

1 +He 4

2+ n1

0H

3

1 +Energy

The energy released per fusion is 2.79 x 10-12 J.

RADIATION AND SAFETY

Why is ionising radiation harmful?

Radiation may be absorbed by the medium it passes through.

Radiation can kill living cells or change the nature of living cells.

The effects of the damage inflicted by the ionising radiation may:

be severe and cause immediate effects, or not become apparent for a long time.

SAFETY MEASURES

1. Wear a radiation badge2. Store radioactive material in lead

containers3. Use forceps / tweezers to handle

radioactive subtances

When working with radioactive materials, observe these precautions:

WHO WILL SURVIVE?

I will survive