Types of Radiation (Cambridge (CIE) IGCSE Physics)

Radioactive decay

• The emission of radiation from a nucleus is spontaneous and random in direction

• This random process of radioactive decay means:

  • 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

Unstable nuclei

• 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

• Instability is commonly due to:

  • The nucleus having too many protons or neutrons

  • The nucleus being very large

• An example of an unstable nucleus is carbon-14

  • This is an isotope of carbon 

    • It has two extra neutrons compared to stable carbon-12

Isotopes of carbon

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

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

Types of radioactive decay

• Radioactive decay is a change in an unstable nucleus that can result in the emission of one of the following types of radiation:

  • Alpha (α) particles

  • Beta (β^-) particles

  • Gamma (γ) radiation

• Remember that these changes are spontaneous and random

Alpha particles

• The radiation 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 radiation 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 radiation 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

Types of radioactive decay

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

Alpha, beta & gamma emission

• 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 the table which shows the following trends down the table:

  • The range increases

  • Penetrating power increases

  • Ionisation decreases

Summary of the properties of nuclear radiation

Penetrating power

• Alpha, beta and gamma radiation have different properties

• So they penetrate materials in different ways

  • This means they are each stopped by different materials

Penetrating power of alpha, beta and gamma radiation

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