Radioactivity

Neutron 

Relative charge --> 0

Relative mass --> 1

Proton

Relative charge --> +1

Relative mass --> 1

Electron

Relative charge --> -1

Relative mass --> 0 (negligible- mass is so small its not worth considering)

This is a typical 4 mark question

• The mass of the nuclear model is concentrated in the centre of the atom, whereas in the plum pudding model the mass is spread out/ distributed evenly

• Electrons in the nucleur model orbit at some distance from the nucleus, whereas in the plum pudding model electrons are embedded in the mass/ positive charge

alpha particles were fired towards a sheet of gold foil

what they observed was:

• The majority of alpha particles went straight through the foil
• few of the particles were deflected through at large angles
• very few of the particles were reflected straight back

They concluded:

• that atoms were mostly space
• the nucleus is very small compared to the size of the atom
• the nucleus contains the mass and positive charge of the atom

Ionising radiation - a type of radiation with enough energy to create ions

The three types:

• Alpha (α ) particles
  
• Beta  (β) particles
• Gamma (γ) particles 

Alpha radiation

Alpha particles are the same as a Helium nucleus

They have 2 protons and 2 neutrons

It has the weakest penatrating power out of the three types of radiation, it can be stopped by paper

However, it is the most ionising

To tell if an element has gone through ALPHA radioactive decay in a nuclear equation:

• the atomic mass should decrease by 4 (as the atomic mass consists of both the neutrons and protons, it goes down by four as the alpha particles emitted have 2 protons 2 neutrons)
• The proton number should decrease by 2 (as alpha particles have 2 protons)

Nuclear equations should be set out like so:

      e.g. 

Beta- (β) - a high energy electron

• created when nucleus has too many neutrons, so the neutron splits into a proton and an electron (which is fired off)

To tell if an element has gone through beta decay:

• The atomic mass should not have changed (the neutron turns into a proton, and they have relatively the smae mass)
• The proton number should have increased by 1 (as a proton is formed)

Nuclear equations of BETA radioactive decay should be set out like this:

Gamma (γ) - a high energy electromagnetic wave

Has the highest penetrating power, it is the most difficult to stop and requires concrete, lead or other heavy sheilding to block them

It is the least ionising type of radiation

Gamma is usually emitted by an atom after it has gone through alpha/beta decay, so it can reach further stability

As alpha particles are positve, they will be attracted to the negative electrode

As beta is an electron (which are negative particles) it will be attracted to the positive electrode

Gamma is a high energy wave (so has no charge) and will go straight through

Alpha and beta are deflected as they are particles, beta is deflected further as it is smaller.

Gamma is not deflected as it is a wave, not a particle

When radiation is emitted towards a Gieger-Muller tube it makes a clicking sound for every particle it detects

How it works:

• The tube is hollow and filled with air, and an electrode is in the middle of it
• when radiation is emitted (as it is ionising) it ionises the particles of air in the tube
• as ions can conduct electricity the electrode becomes charges
• the detection of electricity is what makes the clicking sound

Tracer - radioactive substance injected into the body of a patient, typically used to find blood clots or tumors, the radiactive substance emits radiation outside the body so it can be detected by a machine to form an image on a computer

Gamma is typically used as it is the least ionising, but also because it has the highest penetrating power so the radiation emitted can leave the body to be detected by a computer

The radioactive substance generally should have a short half-life so that it doesn't stay radioactive in the body for too long, it also has to be non-toxic

Killing cancer cells

• gamma radiation is shot at a concentrated beam on a tumor
• it is shot from different directions so it minimises damage to neighbouring cells (giving them a smaller dosage of radiation) while the tumor recieve enough radiation to be killed

Monitoring thickness of materials

• Radioactive particles are fired at a material
• the amount of radioactive substance that is detected through the material at the correct thickness is known
• if the amount of radioactive substance detected is different, the thickness is wrong
• e.g. alpha particles can be stopped by a sheet of paper, if an alpha particle can be detected through a piece of paper the material is too thin.

other uses of radiation:

sterilising medical equipment and foods, carbon dating