All natural elements are present in Earth’s crust in various concentrations. However, only eight of these elements – oxygen, silicon, aluminum, iron, calcium, sodium, magnesium and potassium - make up to 98.5%.

All atoms are constituted from nucleus with positively charged protons and neutrons that have no charge, as well as negatively charged electrons that are at some distance from the nucleus. Combination of different numbers of these three particles make up elements. Atoms of a given element can have different numbers of neutrons and these are called isotopes of the element.

There are two main types of isotopes – stable and unstable or radioactive. Stable isotopes have a stable combination of protons and neutrons that do not undergo decay, whereas radioactive isotopes have an unstable combination of protons and neutrons resulting in radioactive decay.

Radioactive decay is the process by which the nucleus of an unstable atom loses energy by emitting radiation. A material that spontaneously emits such radiation is considered as radioactive. Unstable atoms that are naturally present are indicated as Naturally Occurring Radionuclides (NORs). For example, Thorium and Uranium are unstable or radioactive by nature, so they will disintegrate in time. These elements have always been present on our planet since their half-lives are extremely long. Long-lived radioactive elements and any of their decay products are examples of NORM.

The hazardous elements found in NORM are radium 226, 228 and radon 222 and also daughter products from these radionuclides. Exposure to naturally occurring radiation is responsible for the majority of an average person’s yearly radiation dose and is therefore not usually considered of any special health or safety significance.

NORM levels are typically expressed in one of two ways: Becquerels per kilogram (or gram) indicates level of radioactivity generally or due to a particular isotope, while parts per million (ppm) indicates the concentration of a specific radioisotope in the material.