Types of Radiation (CIE IGCSE Physics)

• Some atomic nuclei are unstable
• This is because of an imbalance in the forces within the nucleus
  • Forces exist between the particles in the nucleus
  • This is commonly due to the nucleus have too many protons or neutrons

• Carbon-14 is an isotope of carbon which is unstable
  • It has two extra neutrons compared to stable carbon-12

Carbon-12 is stable, whereas carbon-14 is unstable. This is because carbon-14 has two extra neutrons

• Some isotopes are unstable because of their large size or because they have too many or too few neutrons

• Unstable nuclei can emit radiation to become more stable
  • Radiation can be in the form of a high energy particle or wave

Unstable nuclei decay by emitting high energy particles or waves

• As the radiation moves away from the nucleus, it takes some energy with it
  • This reduces the overall energy of the nucleus
  • This makes the nucleus more stable

• The process of emitting radiation is called radioactive decay
• Radioactive decay is a random process
  • This means it is not possible to know exactly when a particular nucleus will decay

• It cannot be predicted when a particular unstable nucleus will decay

• This is because radioactive decay is a random process, this means that:
  • There is an equal probability of any nucleus decaying
  • It cannot be known which particular nucleus will decay next
  • It cannot be known at what time a particular nucleus will decay
  • The rate of decay is unaffected by the surrounding conditions
  • It is only possible to estimate the probability of a nuclei decaying in a given time period

• Therefore, the emission of radiation is:
  • Spontaneous 
  • Random in direction

ANSWER:  C

• • Answer A is true. The number of neutrons in a nucleus determines the stability
  • Answer B is true. This is a suitable description of radioactive decay
  • Answer D is true. Radiation is about emissions. It is different to radioactive particles
  • Answer C is not true
  • Radioactive decay is a random process
  • It is not possible to predict precisely when a particular nucleus will decay

• When an unstable nucleus decays, it emits radiation called nuclear radiation
• There are different types of radiation that can be emitted:
  • Alpha (α) particles
  • Beta (β^-) particles
  • Gamma (γ) radiation
• These changes are spontaneous and random

Alpha Particles

• The symbol for alpha is α
• An alpha particle is the same as a helium nucleus
  • This is because they consist of two neutrons and two protons

• Alpha particles have a charge of +2
  • This means they can be affected by an electric field

Beta Particles

• The symbol for beta is β^-
• Beta particles are fast-moving electrons
• They are produced in nuclei when a neutron changes into a proton and an electron
• Beta particles have a charge of -1
  • This means they can be affected by an electric field

Gamma Rays

• The symbol for gamma is γ
• Gamma rays are electromagnetic waves
• They have the highest energy of the different types of electromagnetic waves
• Gamma rays have no charge

Alpha particles, beta particles and gamma waves can be emitted from unstable nuclei

• α, β and γ radiation can be identified by the emission from a nucleus by recalling their:
  • Nature (what type of particle or radiation they are)
  • Their relative ionising effects (how easily they ionise other atoms)
  • Their relative penetrating abilities (how far can they travel before they are stopped completely)

• The properties of Alpha, Beta and Gamma are given in this table, and then described in more detail below

Different Properties of Nuclear Radiation

• The trend down the table shows:
  • The range increases
  • Penetrating power increases
  • Ionisation decreases

Penetrating Power

• Alpha, beta and gamma have different properties
• They penetrate materials in different ways
  • This means they are stopped by different materials

Alpha, beta and gamma are different in how they penetrate materials. Alpha is the least penetrating, and gamma is the most penetrating

• Alpha is stopped by paper, whereas beta and gamma pass through it
• Beta is stopped by a few millimetres of aluminium
  • Gamma can pass through aluminium

• Gamma rays are only partially stopped by thick lead

ANSWER:  B

• • The answer is not A because the radiation passed through the paper almost unchanged
    • This means it is not alpha

  • The answer is not C or D because the aluminium decreased the count-rate significantly
    • This means it is not gamma (gamma penetrates aluminium)
    • This also means it is not neutrons (neutrons penetrate aluminium, however you do not need to know this for your GCSE)

  • Therefore, the source must be Beta particles