234Th

Thorium-234 (234Th) is a radioactive isotope of thorium with 90 protons and 144 neutrons. It is a member of the uranium-238 decay chain and has a half-life of 24.10 days. 234Th decays by beta emission to protactinium-234 (234Pa), which in turn beta-decays to uranium-234 (234U); the chain ultimately leads to stable lead-206.

In nature, 234Th is produced continuously in materials containing uranium-238. In the environment, its relatively short half-life means that 234Th activity reflects recent formation from 238U and its removal from solution or water by adsorption onto particles. Spectroscopic measurements of 234Th often rely on detecting signals from its daughter nuclides or on radiometric techniques that monitor its decay products.

Chemically, thorium is an actinide that typically exists in the tetravalent state and forms insoluble hydroxide compounds under neutral to basic conditions. In environmental systems, 234Th tends to adsorb onto suspended particles, a property that makes it a useful tracer for studying particle dynamics, scavenging, and sedimentation processes.

Applications of 234Th are most prominent in marine science, where it is used as a tracer to estimate particle flux and the rate at which dissolved and particulate material is removed from the water column. By comparing the production rate of 234Th from 238U with its loss to particles, researchers can infer particulate organic carbon flux and other biogeochemical processes. It is also used, to a lesser degree, in hydrology and geochemistry as a short-lived radiotracer.

Safety considerations for 234Th align with its nature as a beta-emitting radionuclide with a finite, relatively short half-life; standard radiological controls apply to handling and measurement.