Physics A-level preparation:Particles:

Isotopes:

Different form of the same element with same no. protons, different no. neutrons

Current nuclear model:

Positively charged nucleus containing neutrons and protons

Nucleus surrounded by negatively charged electrons orbiting it in fixed energy levels

The atom is of neutral charge as there is an equal number of protons and electrons, cancelling out the charge

Radius of atom= 1x10^-10 m

The release and absorption of electrons:

The further away the electron from nucleus, more energy is has, though it doesn't release or absorb as much energy as energy levels are closer

When electrons in inner shells gain energy (by absorbing EM radiation), they move to a higher energy level.

The electrons have been excited

Can only absorb the exact amount that allows them to move between energy levels.

Electrons fall to a lower energy level if they lose energy (by releasing EM radiation

The higher amount of energy that is being gained or lost, the higher frequency of EM radiation.

Further the electron is from nucleus, closer the energy levels so difference in energy gets smaller

Ionisation

Absorbing too much radiation can cause an electron to leave the atom (atom is ionised)

Produces a positive ion

More protons than electrons

Unstable isotopes need to decay into other elements, releasing radiation, in order to become stable (radioactive decay)

Types of decay:

Alpha

Equivalent to a helium nucleus (2 neutrons and 2 protons)

Relative charge: 2+

Relative mass: 4

Highly ionising

Don't penetrate far into materials

Few cm in air, absorbed by a piece of paper

Beta

Beta-minus particle (B-)

Mass: 0

Beta-plus particle (B+)

Relative charge: -1

Fast moving electron released from the nucleus

Fast moving positron released from the nucleus

Positron:

Antiparticle of electron

Same mass, different relative charge

Relative charge: +1

Moderately ionising

Moderately penetrating

Penetrates through a few metres air, absorbed by a sheet of aluminium (approx 5mm thick)

Smaller range than beta minus as annihilation is caused when they hit an electron. Gamma rays are produced

Gamma

Short wavelength EM radiation

Relative charge: 0

Mass:0

Highly penetrating

Absorbed by thick sheets of lead, several metres concrete

Weakly ionising

Used to get rid of energy to stabilise nucleus after other radiation as taken place

Activity and half life:

Activity:

Measured in becquerels (Bq)

Rate of decay

Radiation measured using Geiger Muller counter (clicks when it detects radiation)

Radiation detected by photographic film which becomes darker the more exposed it becomes.

Half life:

Time taken for activity of a source to decay by half

Time for half the undecayed nuclei to decay