Unit 1.2 Basic Ideas about Atoms (pt. 2 Nuclear Structure and Radioactivity) Flashcards
What are radioactive isotopes?
The relative numbers of protons and neutrons in some nuclei make them unstable.
These are called radioactive isotopes.
How do radioactive isotopes become stable?
They become stable through a series of processes of radioactive decay.
List the types of radioactive decay.
- Alpha decay
- Beta-minus decay
- Beta-plus decay
- Electron capture
- Gamma decay
Describe the process of alpha decay.
The nucleus of the radioactive isotope ejects two protons and two neutrons as an ‘alpha particle’
As the nucleus has lost two protons, its proton number decreases by 2 and a new element is formed.
As four nucleons in total have been lost, the mass number decreases by 4.
Describe the process of beta decay
Inside the nucleus a neutron turns into a proton.
The proton number of the atom increases by 1.
The mass number does not change since the neutron and the proton it turns into have the same mass.
Describe the process of beta-plus decay
The proton number decreases by 1.
The mass number does not change since the proton and neutron that it turns into have the same mass.
Describe the process of electron capture.
Write decay equation of positron emission.
Sometimes a nucleus will absorb an electon, turning a proton into a neutron.
The proton number decreases by 1, and the mass number stays the same.
Describe the process of gamma decay.
The unstable radioactive nucleus loses some energy by emitting an electromagnetic wave which makes it more stable.
The wave emitted is called a gamma ray.
There are no changes to the numbers of protons or neutrons and so neither the mass number, proton number, nor element change.
List the properties of alpha particles
- They have a charge of +2 and a mass of 4
- They are strongly ionising because of their high charge, high mass and slow speed.
- They are easily blocked; a thin sheet of paper or few centimetres of air are sufficient.
Why is an alpha-emitter dangerous for the body?
Inside the body, an alpha-emitter is extremely dangerous as the strongly ionising alpha particles will cause significant damage to the DNA in cells, changing the way they function and forming cancerous cells or causing cell death.
Are alpha-emitters safe outside the body?
Yes, because they are eaily blocked and are unlikely to enter cells.
Where do alpha particles bend towards in an electric field?
In an electric field, alpha particles will bend towards a negative plate.
Can alpha particles be deflected?
Yes. They are also deflected by magnetic fields. They move at right angles to the magnetic field with the direction depending on the direction of the magnetic field according to Flemming’s left-hand rule.
List the properties of beta particles.
- They have a charge of -1 or +1.
- They are not as ionising as alpha particles because of their smaller charge, negligible mass and higher speed.
- They interact less with matter and are hence more difficult to block, requiring 1m of air or 5mmof aluminium.
- In an electric field, they will be deflected towards the oppositely charged plate and in magnetic fields they are deflected in opposite directions, again depending on the direction of the field.
- Smaller charge of beta particles mean they experience a weaker force in electric and magnetic fields than alpha particles, but since their mass is significantly less, the force has a greater effect on their motion and so they are deflected more strongly.
How are gamma rays used in medicine?
Gamma rays are used in radiotherapy to shrink tumours by killing cancerous cells.
The rays are aimed from a variety of directions to minimise the damage to healthy tissues by minimising the does that they receive whilst giving a large cumulative dose at the position of the tumour.
List the properties of gamma rays.
- They have no charge
- They are able to knock electrons off of atoms but not as strongly as alpha and beta particles so are only weakly ionising.
- They are the most difficult to block - several centimetres of lead or many metres of concrete are needed.
How are radioactive isotopes used as tracers?
Radioactive isotopes can be used as tracers in industrial and medical contexts.
Once added to a system, radioactive emissions can be detected to follow the path of the isotope to detect blockages leaks, or accumulations of the isotope in the system.
What are beta particles used for?
Beta particles can be used to monitor the thickness of materials like aluminium and ensure a consistent thickness is produced, for example in the production of aluminium foil.
