Kejun Dong

99Tc measurements with accelerator mass spectrometry at CIAE

Abstract 236 U is a long-lived radioactive isotope which is produced principally by thermal neutron capture on 235 U. 236 U may be potentially applied in geological research and nuclear safeguards. Accelerator mass spectrometry is presently the most sensitive technique for the measurement of 236 U and a measurement method for long-lived heavy ion 236 U has been developed. The set-up uses a dedicated injector and the newly proposed 208 Pb 16 O 2 - molecular ions for the simulation of 236 U ion transport. A sensitivity of lower than 10 −10 has been achieved for the isotopic ratio 236 U/ 238 U in present work.

Study on UF - 2 Extraction in Accelerator Mass Spectrometry Measurement of 236 U

This study extracts UF-2 ions from UF4 sample material for the first time so as to improve the measurement accuracy and sensitivity for accelerator mass spectrometry (AMS) measurement of 236U. Compared to the commonly used UO-/UO2 (or U3O8) combination, the UF-2/UF4 approach brings a higher beam current of extracted U-containing ions and lower interference from U isotopes (235U in particular). The UF4 prepared with the procedures developed in this work can provide a higher ratio of F- /O- and therefore lower interference from O-containing 235U and 238U molecular ions, compared with that from the UF4 made by conventional liquid-phase reaction. The AMS experiment was carried out on the AMS system at China Institute of Atomic Energy (CIAE), where only a simple surface barrier detector was used to record ions and a reference 236U sample with a 236U/238U ratio of 10-10 was analyzed. The result shows that the measurement sensitivity of the UF-2/UF4 approach is lower than 10-10 and that the reference 236U sample result is in agreement with the reference value within the uncertainty limits, with the relative uncertainty only 4%. In comparison, the measurement sensitivity of the UO- /U3O8 combination approach is 10-9, and it cannot give a concrete value for the same reference sample using the same AMS system. If the sophisticated 500-ps-resolution time-of-flight detection system is used in combination with the UF-2/UF4 approach, a sensitivity of 10-13 (or lower) is expected.

AMS Measurement of 237 Np at CIAE

237 Np (≃2.14 × 10 6 yr half-life) is potentially applicable in studies on nuclear safeguards and radioactive waste migration. The atomic ratio of 237 Np/U in nature is 10 −12 or even lower, depending strongly on the integral neutron flux received by the material. As an ultra-sensitive technique, accelerator mass spectrometry (AMS) is the best for measuring ultratrace 237 Np. By extracting negative molecular ions NpO – from the oxide sample using 238 UO – and 208 Pb 16 O 2 – pilot beams for the simulation of 237 Np ion transport, identifying the interference isotopes by high-resolution dedicated injector, electrostatic analyzer, and time of flight (TOF) detector, a method for AMS measurement of 237 Np was set up on the HI-13 accelerator at the China Institute of Atomic Energy (CIAE). A sensitivity of –11 has been achieved for the isotopic ratio 237 Np/ 238 U.

The AMS Measurements and Its Applications in Nuclear Physics at China Institute of Atomic Energy (CIAE)

Accelerator Mass Spectrometry (AMS), initiated in late 1970s at McMaster university based on the accelerator and detector technique, has long been applied in the studies on archaeology, geology, and cosmology, as a powerful tool for isotope dating. The advantages of AMS in the analysis of rare nuclides by direct counting of the atoms, small sample size and relatively free from the interferences of molecular ions have been well documented. This paper emphasizes that AMS can not only be used for archaeology, geology, environment, biology and so on, but also served as a unique tool for nuclear physics research. In this paper, the determination of the half‐lives of 79Se, the measurements of the cross‐sections of 93Nb(n,2n)92gNb and 238U(n,3n)236U reactions, the detection and determination of ultratrace impurities in neutrino detector materials, and the measurement of the fission product nuclide 126Sn, are to be introduced, as some of examples of AMS applications in nuclear research conducted in AMS lab of Chi...