Matter and radiation

A breakdown of the matter and radiation section of the course with all the basic facts and knowledge required. 

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  • Created by: EmilyJ
  • Created on: 05-01-13 13:20

Inside the Atom

Atom consists of:

  • Positively charged nucleus made up of nucleons (protons and neutrons)
  • Electrons orbiting nucleus

Electrons have a negative charge; Protons have a positive charge; neutrons have no charge

Protons have a charge of +1.60 x 10^-19 C relative charge = +1

Electrons have a charge of -1.60 x 10^-19 C relative charge = -1

An isotope is an atom with the same number of protons but a different number of neutrons

Z represents the atomic number (number of protons) 

A represents the mass number (number of nucleons) 

Specific charge is charge divided by mass

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Stable and unstable Nuclei

The strong nuclear force holds the nucleus together; It overcomes electrostatic repulsion

It has a short range of about 3fm

Atoms can decay if the are in an unstable state:

  • Alpha decay - two protons and two neutrons are given off as an alpha particle. This change the element, Z decreases by 2, A decreases by 4
  • Beta decay - A fast moving electron is given off. A neutron in the nucleus changes to a proton. An antineutrino is also emitted. This changes the element, Z increases by 1, A is unchanged
  • Gamma decay - electromagnetic radiation. Emitted by a nucleus with too much energy after alpha or beta decay
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Photons

A photon is a packet of light or a burst. 

The photon theory was coined by Einstein to explain the photoelectric effect

The energy of a photon depends upon it's frequency, hence the equation: 

photon energy:  E = hf 

h is the constant known as the Planck constant; the value of h is 6.63 x 10^-34 Js

A laser beam is made up of photons all of the same frequency

The power of the beam = nhf

n is the number of photons passing a point each second

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Particles and Antiparticles

A positron (the antiparticle of an electron) is formed when a proton in an unstable nucleus changes into a neutron. Positron isotopes are not naturally occurring they have to be synthesised

Antimatter was predicted by Paul Dirac, he theorised that:

  • for every antiparticle there is a corresponding antiparticle
  • they annihilate upon meeting forming a pair of photons
  • the antiparticle the same rest mass as the particle
  • the antiparticle has the opposite charge to the particle

He also predicted pair production; A photon with enough energy can become a particle and antiparticle. This usually occurs near a nucleus. The antiparticle will annihilate quickly with matter. 

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How Particles interact

Richard Feynman said that when particles interact through the electromagnetic force a virtual photon is exchanged. (Virtual means that we can only detect their effects it is very hard to detect the particle) 

These interaction particles are called bosons

In the weak nuclear force the bosons are the W+ W- and W0 bosons 

W bosons have:

  • a rest mass of above zero
  • a very short range (around 0.001fm) 
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