Topic 6: Radioactivity Flashcards
State the sub-atomic particles in the atom, their charge and location.
- Positively charged protons in the nucleus
- Neutrally charged neutrons in the nucleus
- Negatively charged electrons that orbit the nucleus in shells (rings) in different fixed distances
Describe the size and mass of the nucleus in relation to the rest of the atom.
- Radius of nucleus is a lot smaller than radius of atomic
- Most of an atom’s mass is concentrated in the nucleus
State the relative mass and charge of the sub-atomic particles:
1. Proton
2. Neutron
3. Electron
4. Positron
- 1, +1
- 1, 0
- 0.0005, -1
- 0.0005, +1
State the size of an atom.
~0.1 nanometres
What is an isotope?
- atoms of the same element with the same number of protons but a different number of neutrons
What occurs when electrons change orbit (move closer or further to the nucleus), in terms of electromagnetic radiation?
- When electrons move to a higher orbit (move further away from the nucleus), the atom has absorbed electromagnetic radiation.
- When electrons fall to a lower orbit (move closer to the nucleus), the atom has emitted electromagnetic radiation.
What is required for an electron leave an atom?
- enough energy
State the types of decay (5).
- Alpha
- Beta Minus
- Beta Plus
- Gamma
- Neutrons
Describe alpha decay.
- a helium nucleus
- highly ionising
- weakly penetrating
Describe beta minus decay.
- electron
- medium ionising
- medium penetrating
Describe beta plus decay.
- positron
- medium ionising
- medium penetrating
Describe gamma decay.
- radiation
- low ionising
- highly penetrating
What is background radiation?
- weak radiation that can be detected from natural or external sources
Give examples of background radiation.
- cosmic rays
- radiation from underground rocks
- nuclear fallout
- medical rays
What are two methods of measuring radioactivity?
- photographic film
- Geiger-Muller Tube
Describe the purpose and use of photographic film when measuring radioactivity (2).
- the initially white film becomes darker when it absorbs radiation
- worn as bandages by people who work with radiation to check how much exposure they have had
Describe the purpose and use of the Geiger-Muller Tube when measuring radioactivity (3).
- it is a tube that detects radiation
- each time it absorb radiation it sends and electrical pulse to the machine which produces a clicking sound
- the greater the frequency of clicking sounds, the more radiation present
How did the atomic model change over time? (4)
- Dalton - Everything was made up of atoms
- JJ Thompson - Discovered the electron (plum pudding model)
- Rutherford - Discovered most of the atom’s mass is located in the nucleus (good foil experiment)
- Bohr - Discovered that electrons orbit the nucleus in fixed rings
Describe (radio) activity? (2)
- number of decays in a sample per second
- measured in Bequerel, Bq
What is the relationship between atom concentration in a sample and the chance that the atoms will decay?
- the greater the concentration of atoms in a sample, the more likely at least one of them will decay
What is the half-life of an isotope?
- the time taken for half the nuclei in a sample to decay
What is the formula for net decline?
net decline = (initial number - number of X half lives) / (initial number)
State uses of radioactivity. (3)
- smoke alarms
- irradiation of food
- diagnosis and treatment of cancer
How is radioactivity used in smoke alarms?
- americium emits alpha particles that are stopped in air as it is weakly penetrating
- alpha particles ionise air particles and makes them charged, making a current
- if smoke enters the air around the smoke alarm, the current drops in the circuit
- causing the alarm to sound