1. Nuclear Reactions

2. X A Z A = number of protons + number of neutrons Z = number of protons
A – Z = number of neutrons
Number of neutrons = Mass Number – Atomic Number

3. U U 235 92 238 92 There are many types of uranium: A 235 Z 92
Number of protons
Number of neutrons
143 A
238 Z 92
Number of protons
Number of neutrons
146
Isotopes of any particular element contain the same number of protons, but different numbers of neutrons.

4. Role of neutrons
The purpose of neutrons in an atom is to balance out the repulsion of protons in the nucleus.
It is like putting items in between opposing magnets.

5. Radioactive Decay
Radioactive decay is due to instability and results in the emission of either:
an alpha particle (a),
a beta particle (b),
or a gamma ray(g).
or a positron emission (e)

6. Alpha Decay The element releases an alpha particle
which is identical to that of a helium nucleus.
(Two protons and two neutrons).
This can be stopped by a thin piece of paper.
The new element has 2 fewer neutrons
and 2 fewer protons.

7. X Y + He Alpha Decay A Z A - 4 Z - 2 4 2 unstable atom alpha particle
more stable atom

8. Alpha Decay Rn
222 86 He 4 2 Ra
226 88

9. Alpha Decay X A Z Y
A - 4
Z - 2 + He 4 2 Ra
226 88 Rn
222 86 + He 4 2

10. Beta Decay
A beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay. Can be stopped by 3 mm of aluminium foil or 10 mm of wood.
Beta decay occurs when a neutron changes into a proton and an electron.

11. Beta Decay
As a result of beta decay, the nucleus has one less neutron, but one extra proton.
The atomic number, Z, increases by 1 and the mass number, A, stays the same.

12. Beta Decay b -1 At
218 85 Po
218 84

13. Beta Decay X A Z Y
Z + 1 + b -1 Po
218 84 Rn 85 + b -1

14. Positron Emission
Positron Emission is where a proton within the nucleus is converted into a neutron, while releasing a positron and an electron neutrino (or X-ray photon.)
This causes the mass number to stay the same, but the atomic number goes down by one.

15. Gamma Decay
Gamma rays are not charged particles like a and b particles.
Gamma rays are electromagnetic radiation with high frequency which are stopped by several cm of lead.
When atoms decay by emitting a or b particles to form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable.
This excess energy is emitted as gamma rays (gamma ray photons have energies of ~ 1 x J).

17. Nuclear Fission
This occurs when a larger nucleus divides to create a smaller nucleus. Alpha decay is a simple version of this. When it divides, it creates a large amount of energy, and often times releases neutrons, which if surrounded by enough fissionable material can lead to a chain reaction. By using control rods to slow the process down, it powers nuclear power plants.

18. Nuclear Fission

19. Nuclear Fusion
This occurs when two smaller nuclei combine together to form a single larger nuclei. This produces far more energy than a fission reaction, and also does not have a dangerous by-product. However we currently don’t have the means to use it as a reliable energy source, as we barely get more energy out, than we put in.

20. Nuclear Fusion