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Nuclear fission

The splitting of a large, unstable nucleus into two smaller nuclei, releasing energy and neutrons.

Nuclear fusion

The joining of two small nuclei to form a larger nucleus, releasing a large amount of energy.

requierments for fission

A large unstable nucleus (e.g. uranium-235) and a slow-moving neutron to start the reaction.

requierments for fusion

Very high temperature and pressure so nuclei have enough energy to overcome electrostatic repulsion.

Job of control rods

Absorb neutrons to control the rate of the chain reaction.

Job of the moderator:

Slow down fast neutrons so they can cause further fission.

Precautions to reduce harm of ionising radiation

Limit exposure time, keep distance, use shielding (e.g. lead), wear protective clothing.

uses of radiation

Medical imaging (X-rays), sterilising equipment, smoke alarms, treating cancer (radiotherapy).

Uses of radioactivity

Cancer treatment, tracers in medicine

Half-life:

The time taken for half of the radioactive nuclei in a sample to decay.

Gamma ray:

High-energy electromagnetic radiation emitted from the nucleus.

Alpha particle:

Two protons and two neutrons (a helium nucleus).

Beta particle:

A fast-moving electron emitted from the nucleus.

Radiation detectors

Geiger muller counter and photographic film

Relative masses

• Proton: 1

• Neutron: 1

• Electron: ~0 (1/1836)

Stopping alpha, beta, and gamma radiation

Alpha: Paper

Beta: Thin aluminium

Gamma: Thick Lead

Mass number (up)Atomic number(down)

Atomic number: Number of protons
Atomic mass: Number of protons+neutrons

Controlled chain reaction

Neutrons cause fission, releasing more neutrons. Control rods absorb excess neutrons so the reaction continues at a steady, safe rate.

Alpha decay

Alpha decay occurs in large, unstable nuclei. The nucleus emits an alpha particle (2 protons and 2 neutrons).
As a result:

• The atom becomes a different element

• Atomic number decreases by 2

• Mass number decreases by 4

What is released in fission

2 smaller nuclei, 2-3 neutrons and energy

isotope

Atoms of the same element with the same number of protons but a different number of neutrons.