Physics - Radioactivity

Radioactivity

The spontaneous emission of radiation by an unstable atomic nucleus

Radioactive decay

when an unstable nucleus loses energy by emitting radiation

ionisation

electrons are knocked out of atoms

ionising radiation

any form of radiation that has the ability to remove electrons from atoms and molecules

Alpha particles

2 protons and 2 neutrons (helium nucleus)

properties of alpha particles

-slow, and large

-highest ionising power

-travels a few centimetres in the air

-Low penetration power (stopped by paper)

Beta particles

fast-moving electrons emitted from the nucleus of radioactive atoms

properties of beta particles

-small and fast

-moderately ionising

-travels 1 m in the air

-medium penetration power (stopped by 5mm aluminium)

Gamma radiation

electromagnetic radiation emitted during radioactive decay and having an extremely short wavelength

Properties of gamma radiation

-wave of energy

-lowest ionising power

-can travel unlimited distances

-high penetrating power (stopped by several centimetres of lead or metres of concrete)

Becquerel

Unit that measures the rate at which a sample of radioactive material decays; 1 Bq = decay of 1 atom or nucleus per second.

half life

the time it takes for half of the radioactive atoms to decay

gold foil experiment

Conducted by Ernest Rutherford in which alpha particles that were shot at gold foil were deflected when they hit the positive center of gold atoms. The nucleus was discovered as a result of this experiment.

How is radiation used in medicine?

-To sterilise equipment: Gamma radiation can kill bacteria cells

-To help treat cancer, as gamma radiation can be used to kill cancer cells

contamination

when radioactive atoms get onto other materials

irridation

exposing an object or a person to nuclear radiation. we use gamma to kill insects, bacteria, fungi, and other organisms in food products

half life calculation formula

final activity = initial activity / 2^n

Nuclear fission

When a large, unstable nucleus absorbs an extra neutron, it splits into two smaller nuclei of roughly the same size. gamma radiation is released.

Spontaneous fission

Fission that occurs without the absorption of a neutron.

Nuclear fission in power stations

Uranium-235 nuclei splits, releasing energy that heats water to turn turbines and generate electricity. Neutrons released from Uranium-235 cause a chain reaction

Nuclear fission in power station safety features

-control rods ( absorb excess neutrons to control the chain reaction)

-moderators (slows down neutrons so they are more likely to cause fission)

-shielding (thick concrete or lead absorbs harmful radiation)

nuclear fusion

when two or more small nuclei fuse to make a bigger nucleus. ssome mass is converted to energy and is transferred as radiation.

conditions for nuclear fusion

high temperature for nuclei to move at high speeds, and high pressure to keep nuclei close enough to fuse. happens in places like stars' cores

hydrogen nuclear fusion

hydrogen + hydrogen → helium + energy