Barium-137 is a radioactive isotope of the element barium, which has the atomic number 56. It is produced as a decay product of cesium-137, a byproduct of nuclear fission. Barium-137 has a half-life of about 2.55 minutes, meaning it takes this amount of time for half of a sample to decay into a stable form, specifically barium-137m, which is a metastable state. Due to its short half-life, barium-137 is primarily used in scientific research and medical applications, such as in radiotherapy for cancer treatment. Its radiation can help target and destroy cancer cells while minimizing damage to surrounding healthy tissue.