GCSE OCR Gateway A Physics Topic 6 - Radioactivity

Nucleon

Proton/ Neutron

Nucleon Number

amount of protons and neutrons in a nucleus

Proton

• symbol: P

• relative charge: 1

• relative mass: 1

• location: nucleus

Neutron

• symbol: N

• relative charge: 0

• relative mass: 1

• location: nucleus

Electron

• symbol: E

• relative charge: -1

• relative mass: 1/2000 (0)

• location: shells

Alpha Emission

• symbol: α

• 2 protons + 2 neutrons

• relative charge +2

• relative mass 4

• range in air a few mc

• stopped by paper

• penetrating power: weak

Beta Emission

• symbol: β

• 1 electron

• relative charge: -1

• relative mass: 1/200-

• range in air: 1 meter

• stopped by: thin aluminium

• penetrating power: medium

Gamma Emission

• symbol: γ

• EM wave

• relative charge: 0

• relative mass: 0

• range in air: near infinite

• stopped by: thick lead

• penetrating power: massive

Emissions ranked by ionising power

1. Alpha (Most momentum)

2. Beta

3. Gamma

What is used to measure radiation

Geiger-muller counter

Units of Radiation

Becquerels (BQ)

Sievert (SV)

Half life

the amount of time it takes for the radioactive activity in a substance to halve

how to calculate radioactive activity after x number of half lives

original activity ⋅ (1/2)^x

(x is the number of half lives)

Contaminated

Radiated from a source internally

Irradiated

Radiated from an external source

Nuclear fission

The process where a neutron collides with a large unstable heavy nucleus (like Uranium) which causes it to split into two smaller nuclei and release energy

What is Fission used for

To generate electricity in a nuclear power plant by using the energy released from the process to boil water into steam and turn a turbine

Chain reaction

When fission takes place and the neutrons released after the nucleus splits invoke fission on other large unstable nuclei

How is Fission controlled in a power station

Control rods made of Boron absorb Neutrons to control the chain reaction

Nuclear Fusion

The Process where two light atomic nuclei (like hydrogen) combine to form a heavier nucleus, releasing energy

Why cant Fusion be reproduced in a reaction

Achieving the conditions required is technologically challening and expensive

Atoms absorbing EM Radiation

• In the photon model EM radiation is emmited as particles of energy (photons)

• when these photons collide with electrons they cause them to move to higher energy levels (excitation)

• when the electrons lose the energy they release the photons (de-excitation)

Continuous Spectra

a diagram showing all the wavelengths of visible light

absorption spectrum

a spectra showing the frequencies of radiation that did not cause an electron to undergo excitation

Emission spectrum

a spectra showing the frequencies of radiation emmited by electrons when they de-excite

Uses of alpha radiation

• Smoke detectors

  • Americium-241 emits alpha radiation

  • alpha radiation ionises oxygen in the air and causes current to flow

  • when current doesnt flow the smoke alarm goes off

  • contamination (of air)

  • long half life

Uses of beta radiation

• testing thickness of paper

  • alpha not penetrative enough

  • gamma too penetrative

  • irradiation

Use of gamma radiation for sterilisation

• irradiates medical equipment

• kills all living organisms without damaging equipment

• short half life

Use of gamma radiation for Treatment

• moveable source of gamma radiation aimed at tumor in body

• tumor gets lethal dose while other cells do not

• irradiation

• short half life

Use of gamma radiation for Diagnosing

• Doctor injects patient with tracer

• radioactive substance absorbed by organs

• gamma radiation detected by gamma camera

• contamination

• short half life