Structure of an atom
A positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons
How can electron arrangements change
- With the absorptions of electromagnetic radiation -> move further away from the nucleus
- By the emission of electromagnetic radiation -> move closer to the nucleus
Mass number
Total number of protons and neutrons in an atom
Atomic number
Number of protons in an atom
Isotope
Elements with the same number of protons but different number of neutrons
Plum pudding model
Suggested that the atom is a ball of positive charge with negative electrons embedded in it
Alpha particle scattering experiment results
- the mass of an atom was concentrated at the centre of
- there was a positively charged nucleus
Nuclear model (Neils Bohr)
Suggested electrons orbit the nucleus at specific distances
James Chadwick
Discovered neutrons
Radioactive decay
When atomic nuclei are unstable and given out radiation as it changes to become more stable
Activity (Bq)
- the rate at which a source of unstable nuceli decays
Count rate
The number of decays recorded each second
Alpha particle
- consists of 2 neutrons and 2 protons (the same as a He nucleus)
- highest ionising power
- travels few cms in air
- stopped by a sheet of paper
- +2 charge
Beta particle
- a high speed neutron ejected from the nucleus turns into a proton and an electron -> the electron that escapes is the beta radiation
- high ionising power
- travels ~1m in air
- stopped by aluminium
- -1 charge
Gamma ray
- high energy EM wave emitted by the nucleus
- low ionising power
- travels unlimited in air
- stopped by lead or concrete
- 0 charge
Name the types of nuclear radiation
- alpha
- beta
- gamma
- a neutron
Half-life
The time it takes for the number of nuclei of an radioactive isotope in a sample to halve
OR the time it takes for the activity from a sample containing a radioactive isotope to half
Radioactive contamination
- the presence of unwanted materials containing radioactive atoms
Irradiation
- the process of exposing an object to nuclear radiation
Protection against irradiation and contamination
- maintaining distance from the radiation source
- limiting time near the source
- shielding from the radiation
(Contamination is harder to remove)
Where does background radiation come from
- natural sources -> rocks and cosmic rays from space
- man-made sources -> fallout from nuclear weapons and nuclear accidents
What is radiation dose measured in
Sieverts (Sv)
1000mSv = 1Sv
Nuclear radiation use for the exploration of internal organs
Gamma emitting tracers are injected -> gamma cameras can then create an image showing where the tracer has gone
-> the half-life of the tracer must’ve be short enough so that most of the nuclei decay shortly after the image is taken to limit patients radiation dose
Nuclear radiation used for the control or destruction of unwanted tissue
- Narrow beams of gamma radiation can be focused in tumour cells to destroy them (gamma used as it can penetrate from outside the body)
- Beta or gamma emitting radiation can be surgically placed inside tumours -> their half-lives must’ve be long enough to be effective, but short enough that it doesn’t continue to irradiate the patient after treatment
