P7- Radioactivity Flashcards
What do radioactive substances contain
Unstable nuclei that become stable by emitting radiation randomly
Isotope
Atoms with the same number of protons, different number of neutrons
Describe the five scientists and discoveries in order
Dalton, invisible objects
Thomson, plum pudding model
Rutherford, nuclear model and nucleus
Bohr, electron shells
Chadwick, neutrons and protons
3 main types of radiation
Alpha
Beta
Gamma
Thomson’s model
Positively charged cloud, with negative electrons scattered throughout
Chadwick’s model
Proton-neutron model
Discovered neutrons
Bohr’s model
Introduced electron shells. In line with Rutherford’s discovery
Why was Thomson’s model no longer accepted?
His plum pudding model had no nucleus, only electrons in a positive cloud. Rutherford discovered the nucleus
Atomic number
Mass number
Number of protons in nucleus
Number of protons plus neutrons in the nucleus
Alpha particle experiment
Who?
What happened?
What did it prove?
Rutherford fired alpha particles at thin gold foil
Particles scattered and some reflected back
Proved tiny, massive, positive, central nucleus
Alpha particle
Description?
Charge?
Relative atomic mass?
2 protons, 2 neutrons, no electrons
2+
4
Alpha particle
Penetration?
Ionising effect?
Uses?
Stopped by single piece of paper, few cm in air
Strongest
Smoke detectors
Beta particle
Description?
Charge?
Relative atomic mass?
Neutron splitting to 1 proton, 1 electron, electron emitted
-1 No mass
Beta particle
Penetration?
Ionising effect?
Uses?
Stopped by mm of aluminium, few m in air
Moderate
Determine thickness of paper
Gamma rays
Description?
Charge?
Relative atomic mass?
Waves of electromagnetic radiation
No charge or mass
Gamma ray
Penetration?
Ionising effect?
Uses?
Stopped by thick lead, few km in air
Weak
Detect leaks in pipes
Activity definition
Unit and measuring device?
Number of decays per second, Becquerels (Bq)
Geiger Muller tube
Alpha particle calculations
Mass and atomic number
Mass number= decreases by 4
Atomic number= decreases by 2
Beta particle calculations
Mass and atomic number
Mass number= stays same
Atomic number= increases by 1
Half life
The time it takes for the activity to fall to half it’s starting level
Half life equation
Count rate after n years= initial count/ 2 to the power of n
Nuclear fission
The process of splitting atomic nuclei, can be used to produce energy for electricity
4 Steps to nuclear fission process
1.Neutron absorbed by nucleus
2. Nucleus splits into 2 daughter nuclei
3. Produces energy and 2 or 3 neutrons
4. Happens in chain reaction
In a nuclear reactor..
Role of water?
Role of control rods?
Role of concrete walls?
Slows down the emitted neutrons as they collide with water molecules
Absorbs surplus neutrons, controls chain reaction
Absorbs ionising radiation
What are the two uses of radiation in medicine
Diagnosis- monitoring internal organs
Treatment- control or destruction of unwanted tissue
Radioactive tracer
How?
Use?
What type?
Eating or injecting a harmless radioactive material
To trace a substance e.g water, through an organ
Gamma, detected outside body, low harm
Radiotherapy
How?
Use?
What type?
High doses of gamma rays
Kills cancerous cells
Gamma, high penetration
Radioactive implants
How?
Use?
What type?
Small pellets in body
Kills cancer cells over time
Beta or gamma with short half-lives
Why is the half life important in medical treatments?
Needs to last long enough for the test to be complete, but decay soon after
Why is the type of radiation important in medical treatments?
Must be detected outside of the body, could need to be strongly penetrating
Examples of background radiation
Radon gas from the ground, food and drink, nuclear weapons testing
Safety precautions of ionisation
Limit time, increase distance, use shielding
Contamination
Unwanted presence of radioactive atoms on a material
Irradiation
Exposing an object to radiation
Ionisation
An atom becoming charged due to losing electrons
Examples of contamination
Fish living in the sea around a nuclear power plant
Breathing in radon gas
Drinking tea with radioactive atoms
Examples of irradiation
Treating fruit with gamma rays to kill bacteria
Sterilising surgical instruments
Factors of contamination
Radioactive source is on or in the object
Difficult to remove all contamination
Radiation can’t be blocked
Factors of irradiation
Object is exposed to radiation
Stops as soon as the source is removed
Can be blocked with shielding
Nuclear fusion
Two nuclei fuse together to make a heavier nucleus
4 Steps to nuclear fusion in stars process
- 2 hydrogen nuclei fuse together
- Forms a helium nucleus
- Releases energy
- Need high temp and pressure
6 features of nuclear fusion
Uses Hydrogen as fuel
Joining of two atoms
Takes place in the sun
Fuel is easily available
Harmless product
Needs high pressure
and temp
5 features of nuclear fission
Uses Uranium as fuel
Splitting of an atom
Causes chain reaction
Often used on earth
Produces nuclear waste
2 similarities of nuclear fusion and fission
Produces energy, can generate electricity
Have been used in a bomb
