1. Should New Zealand remain ‘nuclear power’ free?
AS 91527
PHYS 3.7
Use physics knowledge to develop an informed response to a socio-scientific issue

2. There are equal numbers of Protons and Electrons in the atom. WHY?
PARTICLE
RELATIVE MASS
CHARGE
Proton 1 +
Neutron
Electron -
PARTICLE
RELATIVE MASS
CHARGE
There are equal numbers of Protons and Electrons in the atom. WHY?
This is because they carry opposite charges. If you have an equal number of + and – charges they will cancel each other out so we get a balanced or neutral atom.

3. Is this a stable (balanced) atom?
Why?
What is the MASS NUMBER?
5 (three Protons & two Neutrons)

4. 4 He 2 MASS NUMBER = number of protons + number of neutrons SYMBOL
ATOMIC NUMBER = number of protons

5. BACKGROUND RADIATION
Where does radiation come from and what are the sources of radiation?

6. Background Radiation 13% are man-made Radon gas Food Cosmic rays
Gamma rays
Medical
Nuclear power

7. RADIOACTIVE MATERIALS
Most atoms are stable. However, radioactive atoms are not – they are unbalanced and unstable.
They ‘want’ to become stable (balanced). So to try to achieve this state they emit (give out) energy in the form of radiation.

8. This releases ENERGY. Sometimes a MASSIVE amount of energy.
Can you think of any examples?

9. What are they? TYPES OF RADIATION
How many types of radiation are there and how are they different?
What are they?

10. What do you notice?
So, what is an alpha particle?

11. ALPHA
Alpha particle
Unstable nucleus
New nucleus
Alpha () – an atom decays into a new atom and emits an alpha particle (2 protons and 2 neutrons)
Alpha radiation is the nucleus of a helium atom travelling at extremely high speed.

12. The Atomic number decreases by a value of 1
The Atomic number decreases by a value of 1. It changes a neutron to a proton and releases an electron.

13. BETA
Beta particle
New nucleus
Unstable nucleus
Beta () – an atom decays into a new atom by changing a neutron into a proton and electron.
The fast moving, high energy electron is called a beta particle.

14. The atomic structure doesn’t fundamentally change.
What do you notice?

15. GAMMA
Unstable nucleus
New nucleus
Gamma radiation
Gamma – after  or  decay surplus energy is sometimes emitted. The atom itself is not changed.
Gamma radiation is part of the EM Spectrum.

16. Types of radiation
Alpha () – a high speed helium nucleus is emitted (2 protons & 2 neutrons).
Unstable nucleus
New nucleus
Alpha particle
Beta () – the fast moving, high energy electron is called a beta particle.
Beta particle
Gamma (g) – after  or  decay surplus energy is sometimes emitted. Gamma radiation is a wave with very high frequency with short wavelength.
Unstable nucleus
New nucleus
Unstable nucleus
New nucleus
Gamma radiation

17. PROPERTIES
Alpha, Beta and Gamma all have different properties:
They travel different distances
Different strengths
They are stopped by different
materials.

18. Radioactivity   
Paper Aluminium Thick lead

20. Type of
radiation
Symbol
What is
it made
from?
How far
will it
travel in
air?
What
stops
it?

21.   g   g Type of radiation Symbol What is it made from? How far
will it
travel in
air?
What
stops
it?
Alpha
  
Helium
nucleus. 2
protons &
2 neutrons
 cm
Air /paper
Beta
  
High speed
electron m 
Aluminium
Gamma
  g
High
energy
wave
Lots of m 
Thick lead
&
concrete
Type of
radiation
Symbol
What is
it made
from?
How far
will it
travel in
air?
What
stops
it?
Alpha
  
Helium
nucleus. 2
protons &
2 neutrons
Beta
  
High speed
electron
Gamma
  g
High
energy
wave

22. Nuclear Reactions
Nuclear reactions deal with interactions between the nuclei of atoms
Both fission and fusion processes deal with matter and energy

23. Previous studies have taught us that “matter and energy cannot be created nor destroyed”
We now need to understand that Matter and Energy are two forms of the same thing
Matter and Energy

24. E = mc2 Matter can be changed into Energy
Einstein’s formula above tells us how the change occurs
In the equation below:
E = Energy
m = Mass
c = Speed of Light (Universal Constant)
E = mc2
Energy
Mass
Light
Speed

25. E = mc2 The equation may be read as follows:
Energy (E) is equal to Mass (m) multiplied by the Speed of Light (c) squared
This tells us that a small amount of mass can be converted into a very large amount of energy because the speed of light (c) is an extremely large number
E = mc2

26. Fission may be defined as the process of splitting an atomic nucleus into fission fragments
The fission fragments are generally in the form of smaller atomic nuclei and neutrons
Large amounts of energy are produced by the fission process
Fission

27. Fissile nuclei are generally heavy atoms with large numbers of nucleons
The nuclei of such heavy atoms are struck by neutrons initiating the fission process
Fission occurs due to electrostatic repulsion created by large numbers of protons within the nuclei of heavy atoms
Fission

28. Fission A classic example of a fission reaction is that of U-235:
U Neutron
2 Neutrons + Kr-92 + Ba Energy
In this example, a stray neutron strikes an atom of U It absorbs the neutron and becomes an unstable atom of U-236. It then undergoes fission. Notice that more neutrons are released in the reaction. These neutrons can strike other U- 235 atoms to initiate their fission.

29. The fission process is an a natural one as a French researcher found a natural uranium reactor in Gabon, West Africa; it has been estimated to be over 2 billion years old
Fission produces large amounts of heat energy and it is this heat that is captured by nuclear power plants to produce electricity
Fission

30. Nuclear Fission Neutron induced in U235 Fission is Exothermic
The sum of the masses of
the resulting nuclei is less
than the original mass (about 0.1% less)
The “missing mass” is converted to energy according to E=mc2

31. Neutrons may:
1 - Cause another fission by colliding with a U235 nucleus 2 - Be absorbed in other material 3 - Lost in the system If sufficient neutrons are present, we may achieve a chain reaction
Creates two smaller nuclides and free neutrons
The free neutrons potentially collide with nearby U235 nuclei
May cause the nuclide to split as well
Each split (fission) is accompanied by a large quantity of E-N-E-R-G-Y

32. Fission for nuclear power
Isotopes that undergo fission include uranium-235 and plutonium-239.
There are two major isotopes of uranium – 238 and Uranium-238 is more common, but it does not undergo nuclear fission. Only 0.7% of naturally-occurring uranium is uranium-235.
Most nuclear reactors use uranium-235 which has been enriched to 4%. Nuclear weapons use 90% uranium-235.
The fission of 1 kilogram of uranium-235 releases more energy than burning 2 million kilograms of coal!
Fission for nuclear power

33. Some of the daughter nuclei produced during nuclear fission are stable isotopes, but many are unstable and radioactive, e.g. strontium-90.
Unstable daughter nuclei then decay into other radioactive isotopes.
The decay process continues until a stable isotope is formed.
Daughter products

34. Waste from spent nuclear fuel rods contains highly toxic substances and may remain radioactive for thousands of years. It can harm both people and the environment.
Plutonium-239 can be recovered and used as a nuclear fuel or to make nuclear weapons. Many of the other isotopes in the remaining waste have no practical purpose.
Strict regulations are followed when handling and storing nuclear waste.
Long-term storage of nuclear waste is a major problem. Why is it so difficult to find suitable sites?
Waste products

35. Fusion
Fusion is a nuclear reaction whereby two light atomic nuclei fuse or combine to form a single larger, heavier nucleus
The fusion process generates tremendous amounts of energy; refer back to Einstein’s equation
For fusion to occur, a large amount of energy is needed to overcome the electrical charges of the nuclei and fuse them together

36. Fusion reactions do not occur naturally on our planet but are the principal type of reaction found in stars
The large masses, densities, and high temperatures of stars provide the initial energies needed to fuel fusion reactions
The sun fuses hydrogen atoms to produce helium, subatomic particles, and vast amounts of energy
Fusion

37. Review
Mass and Energy are two forms of the same thing; neither can be created nor destroyed but mass can be converted into energy (E = mc2)
Fission is a nuclear reaction in which a heavy atomic nucleus is split into lighter atomic nuclei
Fusion is a nuclear reaction in which 2 light atomic nuclei are combined into a single, heavier atomic nucleus