There are three types of tracers&colon; bright tracer, subdued tracer and dim tracer. Cu is used in Cu-PTSM as a radioactive tracer for positron emission tomography. Iodine-131 is also used as a radioactive tracer. An imaging tracer made with radionuclides is called a radioactive tracer. Carbon-14 can be used as a radioactive tracer in medicine. Iodine-131 is also one of the most commonly used gamma-emitting radioactive industrial tracer. It is also used as a radioactive tracer in medicine and agriculture. It is widely used as a fluorescent tracer for many applications. Solid shot may contain a pyrotechnic compound if a tracer or spotting charge is used. The Tadje test used cobalt-60 pellets as a "tracer" for determining yield. It is routinely used as a neuronal tracer. M855A1 or M193 ball or M856 tracer ammunition. The second generation was also sold as the Mercury Tracer. However, by mid-1916 an effective mixture of explosive, tracer and incendiary rounds had been developed.