You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Which of the following is a naturally occuring radioactive substance in the body in small quantities? and explain in detail?
Sources of radiation exposure are: Natural sources and Manmade sources. The natural sources include cosmic rays, environmental (terrestrial and atmospheric) radiation, internal radiation (Potassium - 40 & Carbon -14) Man-made Radiation: Medical and dental: X rays, radioisotopes Occupational exposure Nuclear Misc: TV, Radio-active dial watches, Luminous markers Park's Textbook of Preventive and Social Medicine, 25th Edition, Pg 803