The Hindenburg Disaster 1937

MAJOR DISASTERS

The Titanic 1912 Tacoma bridge 1940 Twin Towers 2001

Hiroshima and Nagasaki 1945

Two atomic bombs:

6 th Aug 1945 : Little Boy  Hiroshima

9

th

Aug 1945 : Fat Man



Nagasaki

Form 5 Physics Nuclear Reactions

Fission and Fusion

GEE KUANG BENG SMK METHODIST (ACS)

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 fission  describe Chain reactions  describe and give examples of nuclear fussion  relate release of nuclear energy to the equation E=mc 2  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.

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

1 0 n 235 92 U

The Fission Process The neutron strikes the nucleus which then captures the neutron.

1 0 n 235 92 U

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

236 92 U

The Fission Process The uranium-236 nucleus formed is very unstable.

It transforms into an elongated shape for a short time.

The Fission Process The uranium-236 nucleus formed is very unstable.

It transforms into an elongated shape for a short time.

The Fission Process The uranium-236 nucleus formed is very unstable.

It transforms into an elongated shape for a short time.

The Fission Process It then splits into 2 fission fragments and releases neutrons.

141 56 Ba 92 36 Kr 1 0 n 1 0 n 1 0 n

The Fission Process It then splits into 2 fission fragments and releases neutrons.

1 0 n 141 56 Ba 1 0 n 92 36 Kr 1 0 n

The Fission Process It then splits into 2 fission fragments and releases neutrons.

1 0 n 141 56 Ba 1 0 n 92 36 Kr 1 0 n

The Fission Process It then splits into 2 fission fragments and releases neutrons.

1 0 n 141 56 Ba 1 0 n 92 36 Kr 1 0 n

Nuclear Fission

1 n + 235 U -> 91 Kr + 142 Ba + 3 1 n

Nuclear Fission Examples 235

U

92

+

0 1

n

141 56

Ba +

92 36

Kr + 3

0 1

n

235

U

92

+

0 1

n

138 55

Cs +

96 37

Rb + 2

0 1

n

Energy Released The energy released can be calculated using the equation:

E = mc

2

E m c

2 Where: E = energy released (J) m = mass difference (kg) c = speed of light in a vacuum (3 x 10 8 ms -1 )

Mass-Energy Relationship

• Einstein’s famous equation E = mc 2 • A nucleus is measured to have less mass than the sum of its parts • 12 C 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 235

U

92

+

0 1

n

Element 235 92 U 138 55 Cs 96 37 Rb 1 0 n 138 55

Cs +

96 37

Rb + 2

0 1

n

Atomic Mass (kg) 3.9014 x 10 -25 2.2895 x 10 -25 1.5925 x 10 -25 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):

3.9014 x 10 -25 + 1.6750 x 10 -27 = 3.91815 x 10 -25 kg

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

2.2895 x 10 -25 + 1.5925 x 10 -25 + (2 x 1.6750 x 10 -27 ) = 3.9155 x 10 -25 kg

Energy from Fission

The total mass before fission =

3.91815 x 10 -25 kg

The total mass after fission =

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 Calculate the energy released from the following fission reaction: 235

U

92

+

0 1

n

138 55

Cs +

96 37

Rb + 2

1 0

n

m = 2.65 x 10 -28 kg c = 3 x 10 8 ms -1 E = E E = mc 2 E = 2.65 x 10 -28 x (3 x 10 8 ) 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 10 24 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 10 24 total energy = 6.1056 x 10 13 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.

2 1

H +

1 3

H

4 2

He +

0 1

n +Energy

The Fusion Process 1 2 H 1 3 H

The Fusion Process 1 2 H 1 3 H

The Fusion Process 1 2 H 1 3 H

The Fusion Process 1 2 H 1 3 H

The Fusion Process

The Fusion Process

The Fusion Process

The Fusion Process

The Fusion Process 2 4 He 1 0 n

The Fusion Process 2 4 He 1 0 n

The Fusion Process 1 0 n 2 4 He

The Fusion Process 1 0 n 2 4 He

2 1

H +

3 1 Energy from Fusion

H

4 2

He +

0 1

n +Energy

Element 2 1 H 3 1 H 4 2 He 1 0 n Atomic Mass (kg) 3.345 x 10 -27 5.008 x 10 -27 6.647 x 10 -27 1.6750 x 10 -27

Energy from Fusion Calculate the following: • The mass difference.

• The energy released per fusion.

2 1

H +

3 1 Energy from Fusion

H

4 2

He +

0 1

n +Energy

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

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

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

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

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 2 1

H +

1 3

H

m = 3.1 x 10 -29 kg c = 3 x 10 8 ms -1 E = E 4 2

He +

0 1

n +Energy

E = mc 2 E = 3.1 x 10 -29 x (3 x 10 8 ) 2

E = 2.79 x 10 -12 J

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

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.

1.

2.

3.

When working with radioactive materials, observe these precautions: Wear a radiation badge Store radioactive material in lead containers Use forceps / tweezers to handle radioactive subtances

I will survive