Ionising Power & Deflection (CIE IGCSE Physics)

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• Ionisation is the process of which an atom becomes negative or positive by gaining or losing electrons
• All nuclear radiation is capable of ionising atoms that it hits
  • When an atom is ionised, the number of electrons it has changes
    
• This is mostly done by knocking out an electron so the atom loses a negative charge and is left overall positive

When radiation passes close to atoms it can knock out electrons, ionising the atom

• Alpha is by far the most ionising form of radiation
  • Alpha particles leave a dense trail of ions behind them, affecting virtually every atom they meet
  • Because of this they quickly lose their energy and so have a short range
  • Their short range makes them relatively harmless if handled carefully, but they have the potential to be extremely dangerous if the alpha emitter enters the body

• Beta particles are moderately ionising
  • The particles create a less dense trail of ions than alpha, and consequently have a longer range
  • They tend to be more dangerous than alpha because they are able to travel further and penetrate the skin, and yet are still ionising enough to cause significant damage

• Gamma is the least ionising form of radiation (although it is still dangerous)
  • Because Gamma rays don’t produce as many ions as alpha or beta, they are more penetrating and have a greater range
  • This can make them hazardous in large amounts

 

• The ionising effects depend on the kinetic energy and charge of the type of radiation

• The greater the charge of the radiation, the more ionising it is
  • This means alpha radiation is the most ionising as it has a charge of +2
  • A beta particle has a charge of –1 so is moderately ionising
  • This means gamma radiation is the least ionising as it has a charge of 0 (no charge)

• The higher the kinetic energy of the radiation, the more ionising it is
  • This means alpha particle is still the most ionising because it has the greatest mass
  • However, a beta particle is very light (it is an electron) but travels at high speeds, therefore, it has a lot of kinetic energy and is still moderately ionising
  • Gamma radiation has virtually no mass so is weakly ionising

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• A particle is deflected in an electric field if it has charge
• A particle is deflected in a magnetic field if it has charge and is moving perpendicular to it
  • Therefore, since gamma (γ) particles have no charge, they are not deflected by either electric or magnetic fields
  • Only alpha (α) and beta (β) particles are

Electric Fields

• Alpha particles have a charge of +2 (charge of a helium nucleus)
• Beta particles have a charge of −1 (charge of an electron)
• Therefore, between an electric field created between a negatively charged and positively charged plate
  • Alpha particles are deflected towards the negative plate
  • Beta particles are deflected towards the positive plate
  • Gamma radiation is not deflected and travels straight through between the plates

 

Alpha and Beta particles can be deflected by electric fields

• Alpha particles are heavier than beta particles
  • Therefore, beta particles are deflected more in the electric field and alpha is deflected less

Magnetic Fields

• Similarly, alpha and beta particles are deflected by magnetic fields whilst they are moving
• They are deflected in opposite directions due to their opposite charges

 

Alpha and Beta particles can also be deflected by magnetic fields