Protactinium-231 is a radioactive isotope of protactinium, a rare element found in uranium ores. It has a half-life of about 32,760 years, which means it takes that long for half of a sample to decay. This isotope is primarily produced through the decay of uranium-235 and is used in scientific research, particularly in studies related to nuclear chemistry and geology. Due to its long half-life, protactinium-231 can accumulate in sediments and is often studied to understand the age of geological formations. Its radioactive properties also make it of interest in the field of nuclear energy, although it is not commonly used in practical applications.