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
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
Section 1 of 9Background 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)
Section 2 of 9Natural 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.
Section 3 of 9Man-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.
Section 4 of 9Detecting 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.
Section 5 of 9Corrected 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.
Section 6 of 9Measuring 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.
Section 7 of 9More 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.
Section 8 of 9Key terms
| Term | Meaning |
|---|---|
| Background radiation | Radiation that is always present in the environment. |
| Count rate | Number of decays detected per unit time. |
| GM tube | Geiger–Müller tube, the detector that gives a pulse for each radiation particle. |
| Corrected count rate | Measured count rate minus background count rate. |
| Radon | Radioactive gas that seeps from rocks and emits alpha particles. |
Section 9 of 9Exam technique
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.
Marked practiceQuizzes for this lesson
Last updated:
\n