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In order to improve the accuracy of accelerator mass spectrometry (AMS) measurement for 182Hf/180Hf, a series of measurements have been taken in the AMS laboratory at the China Institute of Atomic Energy (CIAE). The major ones include the instantaneous monitoring of 180HfF−5 current, testing the stability of transmission, the alternate measurements of an unknown sample and standard, and the origin identification and minimization of background 182W. The experimental details and the improvement in the measurement accuracy, as well as some useful suggestions for better satisfying the requirements of certain practical applications, are presented in this paper.

The ratio of 36Cl/Cl can determine the exposure age of surface rocks and monitor the secular equilibrium of 36Cl of sedimentary and igneous rock in groundwater. Due to the uncertainty effects of different chemical separation processes for removing 36S, there is a high degree of uncertainty in 36Cl accelerator mass spectrometry (AMS) measurements if the ratio of 36Cl/Cl is lower than 10−14. A 36Cl AMS higher sensitivity measurement has been set up by using a ΔE-Q3D method at the China Institute of Atomic Energy (CIAE). The performances of ΔE-Q3D method for 36Cl-AMS measurement had been systemically studied. The experimental results show that the ΔE-Q3D method has a higher isobar suppression factor. Taking advantage of direct removing 36S, the sample preparation can be simplified and the uncertainty effects of different chemical separation processes can be reduced in 36Cl AMS measurements.

Accelerator mass spectrometry (AMS) is one of the most promising methods for the measurement of trace amount of 32 Si for its advantages of small sample size, short measurement time and extremely high sensitivity. However, the isobaric interference from 32 S often badly hinders the AMS measurement of 32 Si. The Δ E- Q3D detection technique established in this work brought about an overall suppression factor of larger than 10 12 for 32 S. As a result, a sensitivity of better than 1 × 10 −14 ( 32 Si/Si) has been achieved, based on the measurement of a blank sample.

A new method was developed for AMS measurement of 126Sn. Major features of the method include the preparation of SnF2 samples, the use of SnF2 as target material, the selection of SnF 3 - molecular ions for the AMS measurements, and the quantitative calibration of our Beijing HI-13 AMS measurements by using samples with 126Sn determined by γ-ray spectrometry. The results indicate that the relative uncertainty of the 126Sn/Sn calibrated by γ-ray spectrometry is better than 4% for samples with 126Sn/Sn of 10−8 to −9. A beam current of 126Sn up to 400 nA can be obtained by the combination of SnF2/ SnF 3 - (target sample, selected ions), while 126Te interference was reduced by 2–3 orders of magnitude. A perfect linearity (R2 = 0.99975) between measured and nominal 126Sn/Sn values was obtained by using three standard samples (diluted from the one calibrated by γ-ray spectrometry) with 126Sn/Sn ratios of 1.033 × 10−8, 4.54 × 10−9, 6.43 × 10−10, respectively. A sensitivity of (1.92 ± 1.13) × 10−10 (126Sn/Sn) has been reached by measuring a blank sample.

Isobar interference is the main obstacle for AMS measurement, especially in the case of very strong isobaric interference, such as in the measurement of 32 Si, 53 Mn, 60 Fe, 63 Ni, etc. An isobar separation method with Q3D magnetic spectrometer was developed aiming at AMS measurements for the above-mentioned nuclides. Based on a method of (ΔE-Q3D) the isobaric events can be largely rejected from the region of the nuclide of interest on the focal plane of a Q3D magnetic spectrometer. As a result, the isobaric interference can be reduced by more than three orders of magnitude. Further reduction of isobaric interference can be achieved by the use of a multi-anode ionization chamber placed at the position of collecting the nuclide of interest. The performance of the ΔE-Q3D system for isobar separation was tested by the above-mentioned nuclides with atomic numbers from 14 to 42. The results showed that ΔE-Q3D method has strong capability for separating isobars, as detailed in this paper.

236U is a long-lived radioactive isotope which is produced principally by thermal neutron capture on 235U. 236U may be potentially applied in geological research and nuclear safeguards. Accelerator mass spectrometry is presently the most sensitive technique for the measurement of 236U and a measurement method for long-lived heavy ion 236U has been developed. The set-up uses a dedicated injector and the newly proposed 208Pb16 O 2 - molecular ions for the simulation of 236U ion transport. A sensitivity of lower than 10−10 has been achieved for the isotopic ratio 236U/238U in present work.

A new method for the preparation of 237 Np/ 238 U laboratory standards for accelerator mass spectrometry (AMS) measurement was developed at China Institute of Atomic Energy (CIAE). 237 Np was generated by β-decay (6.75 days) of 237 U produced via fast neutron induced 238 U(n,2n) 237 U reaction. The 58 Co(n,2n) 59 Co and 93 Nb(n,2n) 92m Nb reactions were used to monitor the integral incident neutron flux. The cross-section of 238 U(n,2n) 237 U was determined by measuring the emission rate of 208.0 keV γ-rays from 237 U decay with a calibrated HPGe γ-ray spectrometer at CIAE. In order to correct for the self-attenuation of 208.0 keV γ-ray in the U sample, a 177 Lu–U method was introduced. The new correction method provided effective and high quality measurements of the cross-section for the 238 U(n,2n) 237 U reaction; and the 237 Np/ 238 U ratio. A series of AMS standards for 237 Np/ 238 U (10 −9 –10 −13 ) can be obtained by successive dilution of the original standard sample.

79Se is a long-lived fission product with chemical and radiological toxicity. It is one of the radionuclides of interest in nuclear waste disposal due to its potential migration capacity to the surface environment. Furthermore, 79Se is an ideal tracer in biomedicine. One of the major obstacles in the measurement of ultratrace 79Se with AMS is the strong interference from the isobaric nuclide 79Br. This paper presents a new ultra-sensitive method for 79Se measurements with AMS. The novel aspects of our procedures include the extraction of SeO 2 - molecular ions, that results in a suppression of 79Br background by as much as about five orders of magnitude; the selection of Ag2SeO3 as the chemical form of Se in the target sample, that brings about a relatively large and stable SeO 2 - beam current; and the renovation of the multi-anode detector, that makes 79Se better identified from the interfering nuclide 79Br. By using these procedures, a sensitivity of better than 1.0 × 10−12 has been achieved for 79Se/Se measurement with the CIAE-AMS system. It is then possible to quantify the tracer 79Se in biological samples. Recently, we are prepared to develop the 79Se-AMS biological tracer methodology.

Some long-lived nuclides, such as 36Cl, 41Ca, 53Mn, 79Se, etc., are very interested in life science, environment science, geo- and cosmo-sciences, nuclear wastes management, and other fields. Taking the advantages in high sensitivity and the strong ability to reduce the interferences from molecular ions and isobars, AMS has been one of the most promising methods for the measurement of these nuclides. However, the sensitivity of AMS is often unsatisfactory due to the interferences of stable isobars especially for medium and heavy radioisotopes. Gas-filled time of flight (GF-TOF), Gas-filled Magnet with a time of flight (GFM-TOF), Bragg Curve detector and energy loss (ΔE) combined with a Q3D magnetic spectrometer (ΔE-Q3D) are among the techniques used or being developed in AMS lab of China Institute of Atomic Energy, in an attempt to further reduce the interferences from isobars. These techniques will be tested in our AMS measurement of 53Mn, 79Se, 93Zr, 99Tc, etc., for identifying isobaric interferences.

A new structure of ternary compound ErAlSi was found, and has been studied by means of X-ray powder diffraction technique and refined by Rietveld method. The new structure of the alumosilicide ErAlSi has a tetragonal α-ThSi 2 -type structure, space group I 4 1 / amd (No. 141), Z = 4 and the lattice parameters a = 4.2244(1) A and c = 14.5257(2) A. The magnetic properties of the tetragonal structure of ErAlSi were also investigated. The experimentally determined magnetic effective paramagnetic moment is μ eff = 4.38 μ B per formula unit (4.38 μ B per Er atom). The calculated Currie point is θ P = −26.9 K.

A method for AMS measurement of 32Si has been established at CIAE with the HI-13 Tandem Accelerator and the newly developed ΔE-Q3D detection system. The production of 32Si, the preparation of a set of 32Si reference samples, and their subsequent analysis with the new system are described in detail. An overall suppression factor of more than 1012 for the interfering isobar 32S, resulting in a detection sensitivity below 32Si/Si = 5 × 10−15, has been demonstrated for a limited set of artificially produced samples.

41Ca measurement using CaF− was developed with the CIAE large tandem AMS system with 10 times larger efficiency than using CaF 3 - . The strong 41K interference occurring with CaF− is greatly reduced by both chemistry in the sample preparation and by ion identification method. The background level obtained with blanks was 41Ca/Ca ∼ 1.5 × 10−13.

The long-lived isotope 53Mn cosmogenically produced in situ is a very useful indicator for geochronological dating. A new 53Mn accelerator-mass-spectrometry (AMS) measurement method is developed based on the HI-13 Tandem Accelerator and ΔE-Q3D detection system at China Institute of Atomic Energy. The performance of 53Cr isobar separation and suppression is tested by a series of 53Mn standards and commercial MnO samples. The results show that the ΔE-Q3D detection system brought about an overall suppression factor of more than 107 for the interfering isobar 53Cr.