Radioactive waste is waste type containing radioactive chemical elements that does not have a practical purpose. It is sometimes the product of a nuclear process, such as nuclear fission. The majority of radioactive waste is "low-level waste", meaning it has low levels of radioactivity per mass or volume. This type of waste often consists of items such as used protective clothing, which is only slightly contaminated but still dangerous in case of radioactive contamination of a human body through ingestion, inhalation, absorption, or injection. Waste from the front end of the nuclear fuel cycle is usually alpha emitting waste from the extraction of uranium. It often contains radium and its decay products. The back end of the nuclear fuel cycle, mostly spent fuel rods, often contains fission products that emit beta and gamma radiation, and may contain actinides that emit alpha particles, such as uranium-234, neptunium-237, plutonium-238 and americium-241, and even sometimes some neutron emitters such as Cf. Industrial source waste can contain alpha, beta, neutron or gamma emitters. Radioactive medical waste tends to contain beta ray and gamma ray emitters.