Radioactive decay

What can an unstable nucleus be cause by?

• too many neutrons

• too few neutrons

• too many nucleons in total - too heavy

• too much energy in the nucleus

What happened during a decay?

• energy is released

• and/ord particles are released

What does it mean to be random and spontaneous?

we can’t predict when it will occur

What are the four types of nuclear radiation?

• Alpha

• Beta minus

• Beta plus

• Gamma

Describe each of the types of nuclear radiation

• Alpha = made of 2 protons and 2 neutrons, mass of 4u, charge of +2

• Beta minus = electron, mass is negligible, charge of -1

• Beta plus = positron, mass is negligible, charge of +1

• Gamma = short wavelength, high frequency EM wave, no mass, no charge

What are the types of radiation absorbed by?

• Alpha - paper or few cm of air

• Beta - 3mm of aluminium

• Gamma - many cm of lead

Speed and ionisation ability of each of the types of radiation

• Alpha - slow highly ionising

• Beta - faster medium ionising

• Gamma - very fast (c) not very ionising

Why does alpha have the properties that it does?

• Strongly positive so it can easily pull electrons off atoms - ionising them

• Each time alpha ionises something it transfers energy (loses energy) so it slows down very quick and absorbed quick + low penetration

Why does beta have the properties that it does?

• Much lower mass and charge than alpha

• Less ionisation

• But can travel at higher speeds

• Further penetration

Why does gamma have the properties that it does?

• It is a wave so has a much lower ionisation ability without having any charge or mass

• It can penetrate very far as there is less ionisation

What is the relationship between ionisation and penetration?

The more ionising the less penetrating as it will lose more energy while travelling

How can you use a Geiger muller tube accurately?

Take the count of background radiation first and subtract it from your measurement

What are the different sources of background radiation?

• Rock

• Cosmos

• Food/living organisms contain carbon some will be the radioactive isotope C14

• Nuclear

• Radon gas

• Medicine

What is conserved in a nuclear reaction?

• energy

• momentum

• not mass as it is converted into energy (binding energy)

What happened when is alpha emitted?

• occurs in heavy nuclei

• unstable nuclei

• e.g uranium and radium

What happens when is beta minus emitted?

• in nuclei with many neutrons (more than protons)

• one of the neutron decay into a proton and ejects an electron (beta minus) and an anti neutrino

What happens when is beta plus emitted?

a proton decays into a neutron and a positron and a neutrino

What happens when are gamma rays emitted?

• from nuclei with excess energy

• when nuclei become excited

• energy is lost by emitting a gamma ray

• usually after alpha/beta decay has occurred

• doesn’t cause a change in constituents just a loss in energy

How can you investigate the absorption of gamma radiation by lead?

• Use a micrometer to measure the thickness of some lead sheets at 3 orientations average

• All sheets should be the same thickness

• Turn on the Geiger counter and measure background rate for 5 mins

• Repeat this 3 times and average

• Place the radioactive source at a fixed distance from tube use a meter rule

• Place a piece of lead between the source and the GM tube with a clamp

• Record the count rate of this thickness of lead

• Repeat 3 times and average

• Take away the background count rate = corrected count rate

• Repeat with other thicknesses of leave

• Once finished remove your source immediately - don’t want to be overexposed

• You should see that as thickness increases, the absorption decreases