The ionizing radiations include alpha, beta and gamma radiations. Radioactive atoms emit these radiations. The extent and penetrative powers of these radiations differ.
Alpha radiations are alpha particles consisting of two protons and two neutrons. It is identical in the Helium nucleus. When and alpha particle losses energy, it reduces speed. It attracts electron to its K-shell and become an ordinary Helium atom again. The range in air is 5cm while in tissues is 100um.
Beta radiations exist as negative and positive electrons. Negative electrons are negatrons while the positive electrons are positrons. Beta particles have a range of over 3cm in the air and not more than 1mm in tissues.
Gamma radiations differ from alpha and beta particles. It is electromagnetic. Alpha and beta are particulate. Gamma radiations are in photons or quanta of energy, emitted as a result of nuclear de-excitation. At excited state, nucleons occupy high energy quantum levels. As they return to ground state, they lose excess energy. Gamma radiations penetrate the most. They can penetrate more than 25cm in tissues.
DNA is a double helix structure composed of two strands linked together by hydrogen bonds. Each strand consists of many nucleotide molecules linked together by phosphodiester bonds. Each nucleotide consists of a nitrogenous base. The nitrogenous bases are thymine, adenine, guanine and cytidine (T, A, G and C). These form the condos. The condos are the genetic information that controls the functions of the cells.
Ionizing radiations can break the chemical bonds in DNA. Breaking phosphodiester bonds cause mutations. The mutations can deletions, substitutions, substitutions, translocations and insertions. These mutations affect the functioning of the cells. Their genetic program will differ from normal cells. Affected cells begin multiplying on their own rates unlike the rates of the normal cells. At this level, the affected cells are cancerous cells. This is how ionizing radiations can cause cancer.