Radioactive decay - waves and particles Study Guide

Atoms are the fundamental building blocks of matter, each composed of a nucleus surrounded by electrons. The nucleus contains protons and neutrons. Protons carry a positive charge, neutrons are neutral, and electrons carry a negative charge. In a neutral atom, the number of protons equals the number of electrons. The identity of an element is determined by the number of protons in its nucleus, which is called the atomic number (Z). The total number of protons and neutrons in a nucleus is called the mass number (A). This information is conventionally represented using the notation: ${A}_{Z}\text{X}$, where X is the chemical symbol for the element, A is the mass number, and Z is the atomic number.

For example, a carbon atom with 6 protons and 6 neutrons would be written as ${12}_{6}\text{C}$. Here, 12 is the mass number (6 protons + 6 neutrons) and 6 is the atomic number (number of protons).

Isotopes are atoms of the same element, meaning they have the same number of protons (same atomic number, Z), but they have a different number of neutrons, which results in a different mass number (A). Because they have the same number of protons, isotopes of an element have the same chemical properties. However, their physical properties, such as mass, can differ due to the varying number of neutrons. For instance, carbon-12 (${12}_{6}\text{C}$) and carbon-14 (${14}_{6}\text{C}$) are isotopes of carbon. Both have 6 protons, but carbon-12 has 6 neutrons, while carbon-14 has 8 neutrons. Recognising and interpreting this conventional notation is key to understanding the composition of different atomic nuclei and the concept of isotopes.

Radioactive decay is a natural process where unstable atomic nuclei spontaneously transform into more stable forms by emitting radiation. There are several types of radiation, each causing specific changes to the nucleus's mass (nucleon number) and charge (proton number). Alpha (α) particles are essentially helium nuclei, composed of two protons and two neutrons. When an alpha particle is emitted, the decaying nucleus loses 4 from its mass number and 2 from its atomic number. This changes the element. Beta (β) particles are high-energy electrons ejected from the nucleus when a neutron transforms into a proton. This process increases the atomic number by 1, leaving the mass number unchanged. Again, this changes the element. Gamma (γ) radiation is a form of electromagnetic wave, not a particle, and it is emitted when a nucleus transitions from a higher energy state to a lower energy state, often following alpha or beta decay. Gamma emission does not change the mass number or the atomic number of the nucleus, meaning the element remains the same. Finally, in some very specific nuclear reactions, neutrons can be emitted. When a neutron is emitted, the mass number decreases by 1, but the atomic number (charge) remains unchanged. Understanding these changes is crucial for predicting the products of radioactive decay and balancing nuclear equations. Each emission type has distinct properties, including different penetrating powers and ionising abilities, which are important in various applications and safety considerations.