P5.2.1P5. Nuclear Physics
Detection of radioactivity — Combined Science 0653 - Physics Revision Notes & Topical Questions
5 min read 9 parts Lesson 4 of 8 1 quiz
Lesson summary
P5.2.1 Detection of radioactivity — COMBINED SCIENCE notes: Describe background radiation and how nuclear radiation is detected and measured.Background radiation = the radiation that exists around us all the timeThe count rate of background radiation varies significantly from pla…
- Natural sources
- Man-made sources
- Rocks and buildings
- Radon gas in the air
- Food and drink
- Cosmic rays
Section 1 of 9Background radiation
Background radiation
Background radiation the radiation that exists around us all the time
- The count rate of background radiation varies significantly from place to place.
Natural sources
- Natural sources radioactive elements that have always existed on Earth and in space
Man-made sources
- Man-made sources human activity that adds to the radiation people receive
Section 2 of 9Natural sources
Rocks and buildings
- Rocks and buildings heavy radioactive elements such as uranium and thorium occur naturally in rocks
- Natural radioactivity is also found in building materials such as stone and brick.
Radon gas in the air
- Radon gas in the air uranium decays into radon, which is an alpha emitter
- It is colourless, odourless and tasteless, and is dangerous mainly when inhaled in large quantities into the lungs.
Food and drink
- Food and drink radioactive elements get into food and water from the soil and rocks
- Bananas contain potassium-40, but the amount is minuscule.
Cosmic rays
- Cosmic rays protons from the Sun and from supernovae and other high-energy events enter the atmosphere at high speed
- Their collisions with air molecules produce gamma radiation.
Carbon-14
- Carbon-14 all organic matter contains a tiny amount, and the amount in living things stays almost constant because carbon is constantly replaced
Section 3 of 9Man-made sources
Medical sources
- Medical sources radiation is used frequently in medicine, for example X-rays
Nuclear waste
- Nuclear waste it adds little to background radiation but is dangerous for the people handling it
Nuclear fallout
- Nuclear fallout the radioactive residue thrown into the air after a nuclear explosion
- It is very low at present, but higher where nuclear weapons are tested.
Nuclear accidents
- Chernobyl released a large dose into the environment
- Such accidents are now extremely rare but can devastate areas for centuries.
Largest contributors
- Largest contributors natural sources of radon gas, rocks and buildings, food and drink, and cosmic rays
Section 4 of 9Count rate
- Count rate = the number of decays detected per second or per minute
- The count rate falls as the detector moves further from the source, because the radiation spreads out.
- Count rate in counts per second equals the total counts divided by the time in seconds.
Section 5 of 9Geiger-Müller tube
Geiger-Müller (GM) tube
- Geiger-Müller (GM) tube the most common detector of count rate
- It makes a clicking sound and shows the count rate on a counter or screen.
- A higher frequency of clicks means a higher count rate.
Other detectors
- Photographic film, often used in badges to monitor the dose to workers.
- Ionisation chambers.
- Scintillation counters.
- Spark counters.
Dose
- Dose the amount of radiation received by a person, which must be regulated
Section 6 of 9Corrected count rate
1
Measure the background count with no source present, over a long time for accuracy.
2
Measure the count rate with the source present.
3
Subtract the background count rate from the measured count rate.
4
Use this corrected count rate as the best estimate of the radiation from the source, for example when finding a half-life.
Far from the source
- Far from the source once the count stops falling with distance, the remaining count is background radiation
Random emission
- Random emission counts in equal time intervals vary, and averaging reduces the effect
Section 7 of 9More from the specification
More from the specification
Geomagnetic shielding from solar fields
- Geomagnetic shielding from solar fields terrestrial magnetic fields deflect incoming charged cosmic radiation, shielding the planet and reducing background radiation.
Background radiation
- Background radiation low-level ionising radiation from rocks, cosmic rays, food and medical sources is always present.
Detecting radiation
- Detecting radiation a Geiger-Muller tube and counter records counts per second, and background must be subtracted for the corrected count rate.
Unstable nuclei
- Unstable nuclei an isotope with too many or too few neutrons is radioactive and emits alpha, beta or gamma radiation.
Charge and particles
- Charge and particles alpha is positive helium nuclei, beta is fast electrons and gamma is neutral electromagnetic radiation.
Sample
- Sample measure the count rate of a radioactive sample at a fixed distance and compare with the background count.
Electric field
- A region where a charge experiences a force.
Magnetic field
- Area around a magnet where its effects can be detected.
Kinetic energy
- Energy stored in a moving object.
Background radiation
- Background radiation low-level ionising radiation from rocks, cosmic rays, food and medical sources is always present.
Detecting radiation
- Detecting radiation a Geiger-Muller tube and counter records counts per second, and background must be subtracted for the corrected count rate.
Unstable nuclei
- Unstable nuclei an isotope with too many or too few neutrons is radioactive and emits alpha, beta or gamma radiation.
Charge and particles
- Charge and particles alpha is positive helium nuclei, beta is fast electrons and gamma is neutral electromagnetic radiation.
Sample
- Sample measure the count rate of a radioactive sample at a fixed distance and compare with the background count.
Particle
- A tiny portion of matter that is too small to see.
Neutron
- Neutral particle in the nucleus.
Charge
- A quantity measured in coulombs that is moved round a circuit.
Electron
- Negative particle that moves around the nucleus.
Deflected
- Having its direction changed.
Alpha particle
- A helium nucleus, He2+, used in the scattering experiment.
Penetrating power
- How far radiation travels through a material before it is stopped.
Unstable nucleus
- A nucleus that decays by emitting radiation to become more stable.
Section 8 of 9Key terms
| Term | Meaning |
|---|---|
| Background radiation | The radiation that exists around us all the time from natural and man-made sources. |
| Count rate | The number of decays or counts detected per second or per minute. |
| Geiger-Müller tube | A detector that clicks and gives the count rate of ionising radiation. |
| Corrected count rate | The measured count rate minus the background count rate. |
| Radon | A radioactive gas, an alpha emitter formed by the decay of uranium in rocks. |
| Dose | The amount of radiation received by a person. |
Section 9 of 9Exam technique
1
Thinking background radiation is only man-made — most of it comes from natural sources
2
Thinking the count rate stays the same as the detector moves away — it falls because the radiation spreads out
3
Not correcting for the background — subtract the background count rate from the measured count rate
4
Naming the detector as a radiation detector — name a specific device such as a Geiger-Müller tube
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