Atomic Mass Unit
1/12 the mass of a carbon 12 atom
Mass Defect
- The mass of the nucleus is less than the total mass of the individual particles it contains.
- Strong force causes this as some of the mass is converted into energy to keep the nucleus together.
Thermal neutrons
In thermal equilibrium with moderator.
Low Ek
Control Rods
Absorbs neutrons to prevent further fission. The lower the rods are inserted the more neutrons are absorbed so less fissions occur.
Moderator
Responsible for slowing down neutrons released in fission so they become thermal neutrons and can induce further fission.
Fuel rods
Made of fissile material and each rod contains less than critical mass so reactions don’t become uncontrolled
Coolant
Carries away thermal energy produced by fission reactions
Critical mass
Minimum amount of fissile material needed to maintain a steady flow of fission reactions
What did the Rutherford Scattering experiment do?
Disproved the plum pudding model and provided evidence for the bohr model.
How did the Rutherford scattering experiment work?
- Alpha particles fired at thin sheet of gold foil.
- Most passed through with no deflection suggesting that the atom is mostly empty space.
- Some were deflected by large angles suggesting most of the mass is concentrated in a small positive nucleus.
Alpha radiation
Helium nucleus
Strongly ionising
Slow moving
Stopped by a few cm of air or thin paper
positively charged
deflected in a magnetic field
Beta radiation
High energy electrons or positrons
Mildly ionising
Fast moving
Stopped by thin sheet of aluminium
Negatively or positively charged
Deflected in a magnetic field
Gamma radiation
High frequency em radiation
Weakly ionising
Travels at c
Stopped by a few cm of lead or a few m of concrete
No charge
Unaffected by a magnetic field
Alpha radiation application
Used in smoke detectors:
Alpha particles ionise the air between a source and detector allowing a current to flow
When smoke gets between them it absorbs the radiation
So the air cannot be ionised resulting in no current, which triggers an alarm
Beta radiation application
Used to measure the thickness of aluminium sheets:
An ideal count rate is determined
Material is placed between a beta source and detector
If not enough radiation reaches the detector then the sheet is too thick and the machine flattens it
Otherwise the sheet is too thin and the machine fattens it
Allows for effective quality control
Gamma radiation application
Used to sterilise medical equipment
Used to kill cancerous cells
Used as a medical tracer in diagnosis
Background Radiation
Ionising radiation emitted from a variety of natural and artificial sources.
Corrected count rate
The count rate with the measured count rate deducted
Safety with radiation
Maximise distance with handling tools
Shielding, stand behind absorber such as lead
Background radiation sources
Natural:
Cosmic rays
rocks
radon gas
Artificial:
medical
nuclear fallout
Decay constant
The constant of proportionality, which links rate of decay to the number of undecayed nuclei It is the probability of a decay per unit time.
Half Life
The time taken for half the original number of radioactive nuclei to decay or the time taken for the original activity to half.
Radioactive dating
The use of radioactive isotopes with known half lives to date materials.
Radioactive Decay
The spontaneous disintegration of the nucleus of an atom, which results in the emission of particles.
