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

• 135Cs and 137Cs are present as a result of anthropogenic nuclear activities.
• Measurement has implications for multiple aspects of the nuclear industry.
• Advances in mass spectrometry enable low-level detection of 135Cs and 137Cs.
• Accurate measurement of the 135Cs/137Cs ratio can identify the contamination source.
• Detection limits are controlled by removal of interferences from stable Ba and Cs.

Radionuclides of caesium are environmentally important since they are formed as significant high yield fission products (135Cs and 137Cs) and activation products (134Cs and 136Cs) 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 137Cs, 134Cs and 136Cs are routinely measurable at high sensitivity by gamma spectrometry, routine detection of long-lived 135Cs by radiometric methods is challenging. This measurement is, however, important given its significance in long-term nuclear waste storage and disposal. Furthermore, the 135Cs/137Cs 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 134Cs and 136Cs have a limited application but provide useful early information on fuel irradiation history and have importance in health physics.Detection of 135Cs (and 137Cs) 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