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5.2.3Nuclear Physics

Ionising Power and Deflection — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

5 min read 9 parts Lesson 12 of 17 1 quiz

📚 Cambridge IGCSE Physics 0625 Hub / Topical Revision
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5.2.3 Ionising Power and Deflection — IGCSE PHYSICS notes: Compare the ionising power of alpha, beta and gamma and describe their deflection in electric and magnetic fields.Ionisation = an atom becoming charged by gaining or losing electrons.Process — radiation passing close to a…

  • Electric charge
  • Kinetic energy
  • Inverse link
  • Inside the body
  • Alpha and beta
  • Heavier particles

Part 1 of 8Ionisation (Extended)

1Ionisation
Ionisation an atom becoming charged by gaining or losing electrons.
2Process
  • Process radiation passing close to an atom can knock out an electron, leaving a positive ion.
3Energy
  • Energy each ionisation transfers energy from the radiation, so the more strongly it ionises, the shorter its range.

Part 2 of 8Factors affecting ionising power

Electric charge
  • Electric charge the greater the charge, the more ionising the radiation.
Kinetic energy
  • Kinetic energy the higher the kinetic energy, the more ionising it is.
Alpha
  • Alpha the most ionising, with charge +2 and the greatest mass.
  • It can ionise tens of thousands of atoms in a few centimetres of air.
Beta
  • Beta moderately ionising, with charge −1 and being very light but fast it has a lot of kinetic energy.
Gamma
  • Gamma weakly ionising, with no charge and virtually no mass.

Part 3 of 8Ionisation and penetration

Inverse link
  • Inverse link the better a radiation is at ionising, the less penetrating it is.
Inside the body
  • Inside the body alpha emitters are the most damaging because all the energy is deposited in a small region of tissue.

Part 4 of 8Deflection in fields (Extended)

Deflection in fields (Extended)
Condition
  • Condition a particle is deflected in an electric field if it has charge,
    • and in a magnetic field if it has charge and moves perpendicular to the field.
Gamma
  • Gamma it has no charge, so it is not deflected by either field.
Alpha and beta
  • Alpha and beta they are deflected in opposite directions because of their opposite charges.
Heavier particles
  • Heavier particles beta particles are deflected more than alpha because they have a far smaller mass.

Part 5 of 8Deflection in an electric field

Alpha
  • Alpha deflected towards the negative plate.
Beta
  • Beta deflected towards the positive plate, and by more than alpha.
Gamma
  • Gamma travels straight through between the plates.

Part 6 of 8Deflection in a magnetic field

Alpha and beta
  • Alpha and beta they are deflected while moving, in opposite directions, at right angles to their motion.
Left-hand rule
  • Left-hand rule treat the particles as a current, and for beta the conventional current is opposite to the motion.
Gamma
  • Gamma carries straight on.

Part 7 of 8Summary of the patterns

PropertyAlphaBetaGamma
Charge+2−10
MassLargeVery smallNone
Ionising powerStrongModerateWeak
DeflectionSlight, towards the negative plateLarge, towards the positive plateNone

Part 8 of 8More from the specification

More from the specification
Magnetic and electrostatic deflection
  • Magnetic and electrostatic deflection observing trajectories through electric and magnetic fields provides a diagnostic means to determine particle charge polarity.
Decay equation
  • An equation in nuclide notation with balanced nucleon and proton numbers.
Radioactive
  • Describes a nucleus that decays spontaneously and randomly.
Half-life
  • Time for half the nuclei of an isotope to decay.
Isotope
  • Atom of the same element with a different number of neutrons.
Activity
  • Number of decays per second of a sample.
Background radiation
  • Radiation that is always present in the environment.
Radioactive decay
  • Natural process in which unstable nuclei release energy.
Alpha decay
  • Loss of 2 protons and 2 neutrons.
Unstable nucleus
  • A nucleus with an imbalance of protons and neutrons that may decay.
Alpha particle
  • Alpha particle a helium nucleus made of two protons and two neutrons, with charge +2.
Absorber test
  • Absorber test a source whose count rate barely falls with paper but drops sharply behind thin aluminium emits beta radiation.
Geiger–Müller tube
  • Geiger–Müller tube also called a GM tube or Geiger counter; it detects ionising radiation and counts it.

Key terms

TermMeaning
IonisationRemoving or adding electrons to make an atom charged.
Ionising powerHow strongly radiation ionises atoms.
DeflectionChange in direction of a charged particle in a field.
Electric fieldRegion where a charged particle feels a force from charged plates.
Magnetic fieldRegion where a moving charged particle feels a force.

Avoid these mistakes

1
Saying gamma is deflected by a magnetic field — it has no charge.
2
Saying alpha and beta curve the same way — their charges are opposite.
3
Thinking the more penetrating a radiation is, the more ionising it is — it is the reverse.
4
Believing alpha is deflected more than beta because it has greater charge — beta is lighter and deflects more.

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