Determination of 135Cs and 137Cs in environmental samples: A review

Radionuclides of caesium are environmentally important since they are formed as significant high yield fission products (Cs and Cs) and activation products (Cs and Cs) during nuclear fission. They originate from a range of nuclear activities such as weapons testing, nuclear reprocessing and nuclear fuel cycle discharges and nuclear accidents. Whilst Cs, Cs and Cs are routinely measurable at high sensitivity by gamma spectrometry, routine detection of long-lived Cs by radiometric methods is challenging. This measurement is, however, important given its significance in long-term nuclear waste storage and disposal. Furthermore, the Cs/ Cs ratio varies with reactor, weapon and fuel type, and accurate measurement of this ratio can therefore be used as a forensic tool in identifying the source(s) of nuclear contamination. The shorter-lived activation products Cs and Cs have a limited application but provide useful early information on fuel irradiation history and have importance in health physics. Detection of Cs (and Cs) is achievable by mass spectrometric techniques; most commonly inductively coupled plasma mass spectrometry (ICP-MS), as well as thermal ionisation (TIMS), accelerator (AMS) and resonance ionisation (RIMS) techniques. The critical issues affecting the accuracy and detection limits achievable by this technique are effective removal of barium to eliminate isobaric interferences arising from Ba and Ba, and elimination of peak tailing of stable Cs on Cs. Isobaric interferences can be removed by chemical separation, most commonly ion exchange chromatography, and/or instrumental M AN US CR IP T AC CE PT ED ACCEPTED MANUSCRIPT separation using an ICP-MS equipped with a reaction cell. The removal of the peak tailing interference is dependent on the instrument used for final measurement. This review summarizes and compares the analytical procedures developed for determination of Cs/Cs, with particular focus on ICP-MS detection and the methods applied to interference separation. 1. Sources and properties of caesium isotopes High yield fission products Cs and Cs (Table 1) are present in environmental samples as a result of releases from nuclear power plants and reprocessing sites, nuclear accidents, and fallout from atmospheric weapons testing [1]. Caesium-137 is established as an important radionuclide in radiation protection, environmental monitoring, sediment dating, land erosion and waste disposal [2]. By comparison, Cs is a long-lived radioisotope with a comparatively low radiation risk; however it is a significant contributor to the long term radiological risk associated with deep geological disposal [3]. Furthermore, the Cs/Cs ratio varies with reactor, weapon and fuel type, and therefore can be used as a forensic tool to identify the source of radioactive contamination [1, 4-6]. Other isotopes of caesium include the activation products (Cs and Cs, Table 1). These shorter-lived activation products (2.06 years and 13.2 days, respectively) provide information on fuel irradiation history and have importance in health physics terms but are not considered further here.