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
How is radioactivity use to irradiate food?
- gamma rays transfer to bacteria killing them and sterilising food
- also used to delay ripening of fruit
How is radioactivity used to diagnose and treat cancer? (4)
- patient consumes or is injected with gamma emmiter
- while passing though the body, an external detector can picture where the tracer has collected in the body, which can reveal tumours
- gamma rays are used on the tumour, killing the cancer cells
- however, exposing rays on healthy cells can cause them to mutate
What are the dangers of ionising radiation, in relation to short and long half-lives? (4)
short half- life
- the source presents less risk, as it does not remain strongly radioactive, and quickly dies down
- presents less of a long term risk
long half-life
- the source remains weakly radioactive for a long period of time
- americium used in smoke alarms as it does not need to be frequently replenished and is weak so it will not harm anyone
What are some safety measures when using radioactivity? (2)
- use tracers with short half-life
- leave room during radioactive tests as their health will be at risk in the long term
State the the two different types of radiation?
- Contamination
- Irradiation
Describe contamination in terms if radiation? (2)
- last for a long period of time
- the source of the radiation is transferred to an object (e.g skin)
Describe irradiation in terms of radiation? (2)
- lasts for only a short period of time
- the source emits radiation, which reaches the objects (e.g used medically to kill bacteria)
Describe thoroughly how cancer is treated using radioactivity. (4)
- a beam of gamma radiation rotates around the body
- focuses on tumour and momentarily passes across healthy cells to ensure minimal damage occurs
- takes a long time to fully treat and greater risk of long-term side effects
- a needle which holds radioactive material that directly injects into tumour can also be used
Describe how PET scanners are used in relation to radioactivity? (4)
- radioactive tracer made locally as it has a short half-life and cannot be stored for a long time
- radioactive tracer is inserted into body and is tagged onto desired chemical and travels with it
- scanner records where the tracer emits radioactivity which creates a live 3D visualisation of the body
- used to show effectiveness of treatment or diagnose cancer, epilepsy or Alzheimer’s
How is nuclear power generated?
fission chain reaction - uranium fuel splits releasing neutrons, which are absorbed by further uranium nuclei which split and release two daughter nuclei and two more neutrons, releasing energy
What are the advantages and disadvantages of nuclear power?
Advantages
- no carbon dioxide produced
Disadvantages
- radiation leaking
- stigma around nuclear power by public
- waste disposal is difficult - must be stored deep underground
What are nuclear fusion reactions?
- small nuclei forced together under immense pressure and heat to form a heavier nucleus, releasing energy
- energy source of stars
- electrostatic repulsion between protons means that a lot of energy is required to bring both nuclei close enough to fuse
- expensive and impractical to do on an industrial scale
What is radioactive decay?
- when an unstable nucleus decays into two smaller nuclei, releasing energy
How can a chain reaction be controlled in an industrial setting? (3)
Moderators
- water or graphite
- slows down emitted neutrons to be absorbed to further fissions
Control rods
- these are boron rods in the reactor core, which absorbs excess neutrons, preventing a chain reaction
Water coolant
- heat energy from chain reaction is absorbed by water (coolant)
- water then evaporates into steam and powers the turbine to produce electricity from generator
