What is the meaning of atomic number & mass number?
- Atomic number: No. of protons in the nucleus
- Atomic mass: No. of protons + no. of neutrons
Name some radioactive elements
- Francium (Fr)
- Plutonium (Pu)
- Uranium (U)
- Technetium (Tc)
- Radium (Ra)
What are alpha & beta particles?
- Alpha particles: Helium nuclei ejected from unstable nuclei. Heavily ionising, short range (10 cm), stop easily
- Beta particles: Fast moving electrons ejected from unstable nuclei. Less ionising, travel more, stopped by Al
What are gamma rays?
Gamma rays are photons of high energy EM waves. Takes a lot to stop them (10 cm of Pb, to be precise). Emit ionising radiation by interacting with nearby atoms.
Tell me about radioactive decay
Isotopes of elements will randomly decay, emitting radiation. Alpha & beta emissions cause a change in atomic number. Decay equations must balance
How can radiation be detected?
- Photographic film: Becomes fogged when exposed
- Geiger-Muller tube: When ionising radiation enters the tube, it ionises gases inside, allowing current to pass
Where does background radiation come from?
- Rocks: Slow decay of isotopes of uranium
- Cosmic rays: Explosions of stars
- Medical treatment: Diagnosis & treatment of illnesses
- Nuclear power: Weapon testing, leaks
What is meant by the term “half-life”?
The half-life of an isotope is the time taken for half the original number of unstable nuclei to decay
Where can radioactivity be applied?
- Medicine: Tracers, treatment by killing cells
- Sterilisation: Kills microbes on equipment/food
- Non-medical tracers: Seeing flow of chemicals in industry
- Radioactive dating: Looking at how long ago stuff died
What were the observations from Geiger & Mardsen’s experiment?
- Most alpha particles passed through
- Some were deflected
- Very few bounced back
What is the meaning of the term ‘fissile’?
It refers to isotopes which can be split into lighter elements easily
What affects the amount of deflection of alpha particles shot through a sheet of metal?
- Speed of particles: Faster = smaller angles of deflection
- Nuclear charge: Highly charged = more deflections
- How close the particle gets to the nucleus
What is the unit of radioactive decay?
Becquerel (Bq)
1 Bq = 1 decay per second