Ionizing radiation such as X-rays and radiation from radioisotopes can knock electrons off atoms and produce ions, but cannot be detected by human senses. Devices like Geiger counters, scintillation counters, and film badges can be used to detect and measure different types of ionizing radiation. Radiation has many uses including detecting trace elements, diagnosing and treating diseases like cancer, and tracing chemical reactions and the movement of substances in the body using radioactive tracers.