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7.2.3Nuclear Physics

Background Radiation — Oxford AQA International GCSE Combined Science - Physics Revision Notes & Topical Questions

5 min read 9 parts Lesson 8 of 12

📚 Oxford AQA International GCSE Combined Science - Physics Hub / Topical Revision
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Part 1 of 7What background radiation is

Definition
  • Definition the radiation that is present all around us all the time.
Natural sources
  • Natural sources radioactive elements that have always existed on Earth and in outer space.
Man-made sources
  • Man-made sources human activity adds to the radiation received.
Significance
  • Significance it is not usually dangerous at normal levels, but it must be taken into account in experiments.

Part 2 of 7Natural sources of background radiation

Radon gas
  • Radon gas released from uranium in rocks and soil and collecting in houses and mines, often the largest single source.
  • It is an alpha emitter, tasteless, colourless and odourless, and a risk only if levels are high.
Rocks and buildings
  • Rocks and buildings contain uranium, thorium and potassium isotopes, and granite regions and some building materials give higher levels.
Food and drink
  • Food and drink contain traces of potassium-40 and carbon-14, which become part of our bodies.
    • (for example bananas)
Cosmic rays
  • Cosmic rays high-energy particles from the Sun and space, with a level that is greater at high altitude.
  • Protons from the Sun collide with air molecules and produce gamma radiation.

Part 3 of 7Man-made sources

Medical
  • X-rays, CT scans, radioactive tracers and radiation therapy.
Nuclear weapons fallout
  • Nuclear weapons fallout higher in areas where weapons are tested.
Nuclear accidents
  • Nuclear accidents such as Chernobyl.
Nuclear waste
  • Nuclear waste it adds little to background but is dangerous to those handling it.
Overall
  • Overall man-made sources form a smaller part of the average dose than natural sources.

Part 4 of 7Detecting radiation

GM tube
  • GM tube ionising radiation entering the tube ionises the low-pressure gas, giving a pulse of current that is counted.
Display
  • Display it shows counts or the count rate in counts per second or per minute.
Distance
  • Distance the count rate decreases with distance from the source.
Other detectors
  • Other detectors photographic film (badges), which darkens when exposed, and cloud chambers, which show particle tracks.
Randomness
  • Randomness repeated counts over equal times differ even though the average is steady, so use long counting times and average repeats.

Part 5 of 7Correcting for background (Extended)

Corrected count rate
Corrected count rate measured count rate − background count rate
.
Background reading
  • Background reading measured with the source absent or far away and shielded.
Same units
  • Same units both rates must be in the same units, such as counts per minute.
Half-life experiments
  • Half-life experiments subtract the background from every reading, otherwise the readings never fall to zero.
Distance graph
  • Distance graph the count rate levels off at the background value when the source is too far to be detected.

Part 6 of 7Reducing and measuring the effect

Weak sources
  • Weak sources school sources give a count only a few times the background.
Setup
  • Setup keep other sources in their lead containers, place the source close to the detector and count for a long time.
Typical level
  • Typical level background is about 0.5 to 1 count per second.
Radon areas
  • Radon areas in granite regions radon levels in houses are higher, and sealing floors and ventilation reduce them.

Part 7 of 7More from the specification

More from the specification
Deflection of ionizing radiation in magnetic fields
  • Deflection of ionizing radiation in magnetic fields charged alpha and beta particles curve across magnetic fields, providing a means of identification.
Decay equation
  • An equation in nuclide notation with balanced nucleon and proton numbers.
Kinetic energy
  • K = ½mv2, energy of motion.
Electron
  • Negatively charged particle in an atom.
Radioactive decay
  • Natural process in which unstable nuclei release energy.
Penetrating power
  • How far radiation travels through a material.
Alpha decay
  • Loss of 2 protons and 2 neutrons.
Ionising power
  • How strongly radiation ionises atoms.
Unstable nucleus
  • A nucleus with an imbalance of protons and neutrons that may decay.
Electric field
  • Region of space in which a charge experiences a force.
Magnetic field
  • Area around a magnet where its effects can be detected.
Alpha particle
  • Alpha particle a helium nucleus of two protons and two neutrons, so it carries a charge of +2.

Key terms

TermMeaning
Background radiationRadiation always present in the environment.
RadonRadioactive gas released from rocks.
Cosmic raysHigh-energy particles from space.
Count rateNumber of detected decays per unit time.
Corrected count rateMeasured rate minus background rate.

Avoid these mistakes

1
Forgetting to subtract background from the measured count rate.
2
Saying background radiation comes only from nuclear power stations.
3
Taking only one short count and treating it as exact.
4
Saying radon is a solid — it is a gas that seeps out of rocks.

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