⇒ You would think a group of positively charged protons (in the nucleus) would repel each other, but they don't

⇒ This means there needs to be some attractive and short range force that is stronger than the repulsive force between the protons

⇒ This strong force must also apply equally between protons and neutrons, otherwise it would be very easy to remove neutrons from the nucleus

⇒ Finally, at extremely short distances there needs to be a repulsive force otherwise the protons and neutrons (i.e. nucleons) would collapse and implode in on themselves!

⇒ The strong nuclear force is one of the four fundamental forces of nature. It is a very short-range force and acts between nucleons (protons and neutrons) holding nuclei together and keeping them stable.

⇒ This strong nuclear force is attractive at distances between 0.4 fm (femtometres) and 3 fm (3 x 10^-15

⇒ Below 0.4 fm the force is repulsive

⇒ As you can see from the graph, when the distance is 0.4fm the force is neither attractive or repulsive - where the nucleus is stable, this is the separation of each nucleon

• At this distance, the resultant force on each nucleon is zero

⇒ Also note that when the distance is above 3fm the strong nuclear force drops to 0 too

⇒ Not all nuclei are stable

⇒ Radioactive decay happens in unstable atomic nuclei - that is ones that don't have enough binding energy to hold the nucleus together due to an excess of either protons or neutrons

• This is why the vast majority of isotopes are unstable

⇒ The three most common decay mechanisms are alpha, beta, and gamma decay

⇒ With alpha radiation, alpha particles are emitted

⇒ An alpha particle consists of two protons and two neutrons (this is identical to the nucleus of a helium atom)

⇒ The symbol for an alpha particle can be seen here - it has a proton number of 2 and a mass number of 4

⇒ In this diagram, there is an unstable nucleus on the left, from an element, emitting an alpha particle

⇒ When the alpha particle is emitted, the nucleon number (total number of protons and neutrons) decreases by 4 and the atomic number (number of protons) decreases by 2 in the unstable nucleus

⇒ This change in the number of protons and neutrons will cause the decaying element to transform into a new element

⇒ In shot, beta radiation involves the emission of an electron

⇒ We represent this emitted electron (i.e. our beta particle) using the following symbol:

⇒ When an unstable nucleus of an element emits a beta particle the following happens:

⇒ Essentially, a beta particle (i.e. an electron) is emitted instantly when a neutron in the unstable nucleus changes into a proton

⇒ In addition to this, an antiparticle with no charge, called an antineutrino is emitted

• See our notes on antiparticles and neutrinos for more detail

⇒ The transformation of a neutron into a proton increases the atomic number by 1, but the nucleon number stays the same, causing the decaying element to transform into a new element

⇒ Gamma radiation is electromagnetic radiation emitted by an unstable nucleus

⇒ It has no mass and no charge

⇒ It is emitted from the nucleus where that nucleus has too much energy, following the emission of alpha or beta particles

⇒ During beta radiation a certain amount of energy is emitted. The total energy emitted during beta radiation (E_TOT) is made up of the kinetic energy from the beta particle plus the kinetic energy from the antineutrino

⇒ This graph shows that there is not a single unique kinetic energy for the β− particle

⇒ The observation of a continuous range of β− particle kinetic energies in a given β– decay process is because of the involvement of antineutrinos

⇒ Also see our notes on:

• Introduction to Particles and Nuclides
• The Building Blocks
• Nuclear Radiation
• Nuclear Equations
• Electromagnetic Radiation
• Antiparticles