Question

why isotopes are unstable and why they can emit radiation?

Answer 1

Atoms of the same element with different numbers of neutrons are called isotopes. Many elements have one or more isotopes that are radioactive. These isotopes are called radioisotopes. Their nuclei are unstable, so they break down, or decay, and emit radiation.The nucleus may be unstable because it has too many protons or an unstable ratio of protons to neutrons.

Atoms with an unstable nucleus regain stability by shedding excess particles and energy in the form of radiation. The process of shedding the radiation is called radioactive decay. The radioactive decay process for each radioisotope is unique and is measured with a time period called a half-life. One half-life is the time it takes for half of the unstable atoms to undergo radioactive decay.