Radionuclides in the environment Radionuclides are radioactive isotopes of natural or artificial origin. Their detection, analysis and characterization provide information about the environmental condition of a site, particularly in the vicinity of nuclear facilities, but also contribute to the identification of illicit nuclear activities.     Unique analysis capabilities   The CEA's Environmental Assessment and Monitoring Department (DASE), which comes under the Military Applications Division (DAM), has developed considerable expertise in the fields of radiochemistry and radionuclide measurement. Protocols for effective chemical treatment of environmental samples (biological, water, aerosol, soil samples) enable the separation and purification of specific radionuclides. Measurements are then adapted to requirements, e.g.:   Determining overall β or α activity, Identifying all the γ-emitters in a sample or, conversely, detecting a particular ?-element such as Cesium-137 (137Cs), Accurately determining the isotopic composition of uranium contained in a representative sample of its environment or in a single isolated particle, Distinguishing the fraction of tritium accumulated in organic matter from the water exchangeable fraction.   The Cofrac-accredited DAM test laboratory is distinguished by its specific services, such as mass dosage of plutonium isotopes (239Pu and 240Pu) and its capability for testing large samples with some of the lowest detection thresholds in the world. For certain sample types, this laboratory can measure radionuclide concentration in a millionth of a microgram per gram of analyzed matter.     Committed to the fight against nuclear proliferation   Nuclear tests conducted in the atmosphere result in the emission and propagation of radioactive particles, such as, for example, the xenon isotopes (133Xe, 135Xe), zirconium-95 (95Zr) and baryum-140 (140Ba), ), which are clear test indicators. As part of the International Monitoring System (IMS) requested by the Comprehensive Test-Ban Treaty (CTBT), 80 radionuclide detection stations are planned to be set up, together with 16 laboratories dedicated to supporting the IMS. The CEA, as the technical correspondent for France, is in charge of setting up and running several radionuclide stations. Its radionuclide analysis laboratory was certified by the Comprehensive Test-Ban Treaty Organization (CTBTO) in 2003. The fight against nuclear proliferation and terrorism also involves detecting particular signs of illicit nuclear activity where no nuclear testing is taking place. Within this framework, tritium detection is a particular priority, given that it is a radioactive isotope of the hydrogen family and a good indicator of nuclear activity. The aim is also to seek isotopic evidence of uranium and plutonium as accurately as possible, in a whole sample or in an isolated particle, depending on the context. These isotopic signatures reveal channels linked to the production or trafficking of fissile material. The DASE has recognized expertise, which is why it is also a "support laboratory" within the framework of the safeguard agreements between the International Atomic Energy Agency (IAEA) and the states that signed the Non Proliferation Treaty (NPT).     Environmental monitoring   This takes various forms:   Gamma mapping. The DASE teams have access to mobile (helicopter- or car-borne) devices for mapping gamma emitters contributing to the radiological diagnosis of a site. Comprehensive site survey. This type of survey requires expertise in geology, hydrogeology, geochemistry and metrology. Its purpose is to understand the mechanisms of water and radionuclide transfer in the soil, rocks and the subterranean groundwater based on the geological characteristics of a site and numerous experimental results (measurements and models). Numerical simulation is then used to model the site and plan for development. This work can be accomplished for elements other than radionuclides, such as, for example, heavy metals.