Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

5.2.1Nuclear Physics

Detection OF Radioactivity — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

5 min read 9 parts Lesson 8 of 17 1 quiz

📚 Cambridge IGCSE Physics 0625 Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read
Lesson summary

5.2.1 Detection of Radioactivity — IGCSE PHYSICS notes: Describe background radiation and its sources, measure count rate with a detector and correct for background.Background radiation = the radiation that exists around us all the time.Natural sources — radioactive elements that…

  • Man-made sources
  • Rocks and buildings
  • Food and drink
  • Cosmic rays
  • Nuclear waste
  • Nuclear fallout

Part 1 of 7Background radiation

Background radiation
Background radiation the radiation that exists around us all the time.
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 humans receive.
Variation
  • Variation it varies from place to place and randomly from moment to moment.
    • (for example granite areas and high altitude)

Part 2 of 7Natural sources

Radon gas
  • Radon gas an alpha emitter released from rocks, the largest source and dangerous if inhaled in large quantities.
Rocks and buildings
  • Rocks and buildings uranium and thorium occur naturally in rocks and building materials.
Food and drink
  • Food and drink some foods contain potassium-40, but the amount is minuscule.
Cosmic rays
  • Cosmic rays protons from the Sun and high-energy events in space collide with air molecules and produce gamma radiation.
Carbon-14
  • Carbon-14 all organic matter contains a tiny amount.

Part 3 of 7Man-made sources

Medical
  • X-rays, CT scans, radioactive tracers and radiation therapy.
Nuclear waste
  • Nuclear waste it contributes little to background but is dangerous to handle.
Nuclear fallout
  • Nuclear fallout residue from nuclear weapon tests, which is higher where weapons are tested.
Nuclear accidents
  • Nuclear accidents such as Chernobyl, which are now rare but catastrophic.

Part 4 of 7Detecting radiation

Geiger–Müller (GM) tube
  • Geiger–Müller (GM) tube connected to a counter or ratemeter, it gives a pulse of current each time it absorbs radiation.
Count rate
  • Count rate the number of decays detected per second or per minute.
Distance
  • Distance the count rate falls the further the detector is from the source, because the radiation spreads out.
Other detectors
  • Other detectors photographic film (badges), ionisation chambers, scintillation counters and spark counters.

Part 5 of 7Corrected count rate (Extended)

Corrected count rate
Corrected count rate measured count rate − background count rate
.
Measuring background
  • Measuring background take readings with no source present.
Uses
  • Uses use the corrected rate when finding half-life or comparing sources.
Random decay
  • Random decay counts fluctuate, so measure over a longer time and repeat to find a reliable average.

Part 6 of 7Measuring a corrected count rate

1
Remove all sources and switch on the GM tube and counter.
2
Record background counts over a long time and calculate the background count rate.
3
Place the source at a fixed distance in front of the GM tube.
4
Record counts over a measured time and calculate the count rate.
5
Repeat the readings and average them.
6
Subtract the background count rate to get the corrected count rate.

Part 7 of 7More from the specification

More from the specification
Cloud chamber particle tracks in magnetic fields
  • Cloud chamber particle tracks in magnetic fields curvature of condensation tracks across uniform magnetic fields provides a visible means to identify radiation.
Background radiation
  • Background radiation low-level ionising radiation always present from radon gas, rocks, cosmic rays, food and medical sources
Geiger-Muller tube
  • Geiger-Muller tube detects ionising particles and gives a count rate, which must be corrected by subtracting background count
Unstable nucleus
  • Unstable nucleus an isotope with too many or too few neutrons emits radiation to become more stable
Alpha, beta and gamma
  • Alpha, beta and gamma alpha is a helium nucleus with charge +2, beta is a fast electron, gamma is an electromagnetic wave with no charge
Random decay
  • Random decay it cannot be predicted when a particular nucleus will decay, only the average rate for a large sample;
    • activity is measured in becquerels
Background radiation
  • Background radiation low-level ionising radiation always present from radon gas, rocks, cosmic rays, food and medical sources
Geiger-Muller tube
  • Geiger-Muller tube detects ionising particles and gives a count rate, which must be corrected by subtracting background count
Unstable nucleus
  • Unstable nucleus an isotope with too many or too few neutrons emits radiation to become more stable
Alpha, beta and gamma
  • Alpha, beta and gamma alpha is a helium nucleus with charge +2, beta is a fast electron, gamma is an electromagnetic wave with no charge
Random decay
  • Random decay it cannot be predicted when a particular nucleus will decay, only the average rate for a large sample;
    • activity is measured in becquerels
Penetrating power
  • How far radiation travels through a material.
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.
Decay equation
  • An equation in nuclide notation with balanced nucleon and proton numbers.
Kinetic energy
  • K = ½mv2, energy of motion.
Neutron
  • Neutral particle in the nucleus, relative mass 1.
Charge
  • Quantity of electricity in coulombs, Q = It.
    What the symbols mean: Q = charge (C) · I = current (A) · t = time (s)
Isotope
  • Atom of the same element with a different number of neutrons.
Electron
  • Negatively charged particle in an atom.

Key terms

TermMeaning
Background radiationRadiation that is always present in the environment.
Count rateNumber of decays detected per unit time.
GM tubeGeiger–Müller tube, the detector that gives a pulse for each radiation particle.
Corrected count rateMeasured count rate minus background count rate.
RadonRadioactive gas that seeps from rocks and emits alpha particles.

Avoid these mistakes

1
Forgetting to subtract background from the measured count rate.
2
Saying background radiation comes only from nuclear power stations — most is natural.
3
Taking only one short count and treating it as exact.
4
Mixing counts per second with counts per minute.

Last updated:

\n