**Abstract**

This chapter deals with gamma background radiation that is exposed to two major natural sources: normal sources that are earthly gamma rays and astronomical rays. Earthbound gamma rays from radionuclide elements such as thorium, potassium, and uranium. Also, in building and enhancing materials such as medical plants, building purposes, some vegetables and fruits commonly used in markets and soil. The measurements of gamma background radiation differ according to the purpose. So, there are many instruments used such as HPGe detector, NaI (TI) detector, CR-39, a dosimeter, and SSNDT detector. This research will explain in detail the studies and the mechanism for each detector and how it works and the application (practical) studies for each one. The purpose of calculating gamma background radiation is to be in the safe side for human being according to the international union specified with a standard limitation of world average value or with a specific value ranged (standard values) according to the case study in medical, food, or building materials.

**Keywords:** terrestrial gamma rays, natural gamma ray, background radiation, detectors, annual effective dose, absorbed dose
