Stepped-up development of accelerator mass spectrometry method for the detection of ^(60)Fe with the HI-13 tandem accelerator

The Moon provides a unique environment for investigating nearby astrophysical events such as supernovae.Lunar samples retain valuable information from these events,via detectable long-lived“fingerprint”radionuclides such as^(60)Fe.In this work,we stepped up the development of an accelerator mass spectrometry(AMS)method for detecting^(60)Fe using the HI-13tandem accelerator at the China Institute of Atomic Energy(CIAE).Since interferences could not be sufficiently removed solely with the existing magnetic systems of the tandem accelerator and the following Q3D magnetic spectrograph,a Wien filter with a maximum voltage of±60 kV and a maximum magnetic field of 0.3 T was installed after the accelerator magnetic systems to lower the detection background for the low abundance nuclide^(60)Fe.A 1μm thick Si_(3)N_(4) foil was installed in front of the Q3D as an energy degrader.For particle detection,a multi-anode gas ionization chamber was mounted at the center of the focal plane of the spectrograph.Finally,an^(60)Fe sample with an abundance of 1.125×10^(-10)was used to test the new AMS system.These results indicate that^(60)Fe can be clearly distinguished from the isobar^(60)Ni.The sensitivity was assessed to be better than 4.3×10^(-14)based on blank sample measurements lasting 5.8 h,and the sensitivity could,in principle,be expected to be approximately 2.5×10^(-15)when the data were accumulated for 100 h,which is feasible for future lunar sample measurements because the main contaminants were sufficiently separated.

Preliminary study of^10Be/^7Be in rainwater from Xi'an by Accelerator Mass Spectrometry

The ^10Be/^7Be ratio is a sensitive tracer for the study of atmospheric transport, particularly with regard to stratosphere-troposphere exchange. Measurements with high accuracy and efficiency are crucial to ^7Be and ^10Be tracer studies. This article describes sample preparation procedures and analytical benchmarks for ^7Be and ^10Be measurements at the Xi＇an Accelerator Mass Spectrometry（Xi＇an-AMS） laboratory for the study of rainwater samples. We describe a sample preparation procedure to fabricate beryllium oxide（Be O） AMS targets that includes co-precipitation, anion exchange column separation and purification. We then provide details for the AMS measurement of ^7Be and ^10Be following the sequence BeO^-→Be^2＋→Be^4＋ in the Xi＇an- AMS. The ^10Be/^7Be ratio of rainwater collected in Xi＇an is shown to be about 1.3 at the time of rainfall. The virtue of the method described here is that both ^7Be and ^10Be are measured in the same sample, and it is suitable for routine analysis of large numbers of rainwater samples by AMS.

Primary result of ^(236)U measurement with accelerator mass spectrometry at CIAE

The rare isotope ^236U has a half-life of 2.342（3）×107 years, and is produced principally by thermal neutron capture on ^235U. The isotopic atom ratio of ^236U/^238U depends on the integral thermal neutron flux received by the material of interest. ^236U is potentially useful as a ＂fingerprint＂ for indicating the presence of neutron-irradiated uranium usually originating from nuclear activity. By extracting negative molecular ion UO^- from the uranium oxide target, simulating the ^236U^16O^- beam transport with ^238U^16O^- and ^208Pb2^16O^- pilot molecular ion beam, transporting the ^236U-containing ion beam with a high resolution injection magnet analyzer and electrostatic analyzer system, and finally identifying and detecting ^236U with a time-of-flight detector （TOF）, a method for AMS （Accelerator Mass Spectrometry） measurement of ^236U was established on the HI-13 Accelerator AMS system at China Institute of Atomic Energy.

Measurement of ^(129)I in ferromanganese crust with AMS

In the present study, the analytical method for ^129iodine （^129I） in ferromanganese crusts is developed and ^129iodine/^127iodine （^129I/^127I） ratio in ferromanganese crusts is measured by the accelerator mass spectrometry （AMS）. The developed method is applied to analyze ^129I/^127I ratio in two ferromanganese crusts MP5D44 and CXD08-1 collected from the Mid-Pacific Ocean. The results show that ^129I/^127I ratio in MP5D44 and CXD08-1 crusts varies from 7×10^-14 to 1.27×10^-12, with the lowest value falling on the detection limit level of AMS reported by previous literatures. For the depth distribution of ^129I/^127I, it is found that both MP5D44 and CXD08-1 crusts have two growth generations, and the ^129I/^127I profiles in two generations all displayed an approximate exponential decay. According to the ^129I/^127I ratio, the generate age of bottom layer of MP5D44 and CXD08-1 was estimated to be 54.77 and 69.69 Ma, respectively.

Frontier applications of electrostatic accelerators

Electrostatic accelerator is a powerflfl tool in many research fields, such as nuclear physics, radiation biology, material science a.rchaeology and earth sciences. Two electrostatic accelerators, one is the single stage Vail de Gi＇aaff with terminal voltage of 4.5 MV and another one is tile EN tamteIn with terminal voltage of 6 MV, were installed in 1980s and had been put into operation since the early 1990s at tile Institute of Heavy Ion Physics. Marly applications have been carried out since then. These two accelerators are described and summaries of the most important applications on neutron physics and technology, radiation biology and material science, as well as accelerator mass spectrometry （AMS） are presented.

The initial exploration for ^(26)Al chronology in deep-sea ferromanganese crust

Background The deep-sea ferromanganese crust(DSFC)is a natural archive for recording the history of the Earth’s evolution,as one of the most common authigenic assemblages in marine sediments.Although the depositional age dating using meteoric ^(10)Be has been successfully used in the study on the chronology of DSFC,the research on ^(26)Al has not seen relevant reports in this aspect due to the influence of factors such as measurement sensitivity and ^(26)Al in situ production.Method The first exploration for ^(26)Al chronology in DSFC was carried out by using accelerator mass spectrometry(AMS)measurements of ^(10)Be and ^(26)Al,and the comparison of relationship between isotopic ratios and concentrations of Al and Be.Results The growth rates of G.R=(1.44±0.09)mm/Ma,(3.58±0.29)mm/Ma,(1.52±0.10)mm/Ma and(2.93±0.14)mm/Ma are derived using ^(10)Be/^(9)Be,^(26)Al/^(27)Al ratios,^(10)Be and ^(26)Al concentrations,respectively.Conclusion The ^(26)Al chronological methods have been explored based on a DSFC sample and encouraging results were obtained.The results are preliminary and insufficient;some information is still needed to explain the difference between ^(26)Al and ^(10)Be chronology.

Cross-section measurement for the ^(93)Nb(n,2n)^(92g)Nb reaction at the neutron energy of 14.6 MeV by the AMS method

The cross-section for the 93Nb（n, 2n）92gNb reaction has been measured at the neutron energy of 14.6 MeV using neutron activation and accelerator mass spectrometry （AMS） determination of the long-lived product nuclide 92gNb. The neutron energy was generated from the D＋T neutron source at the China Institute of Atomic Energy （CIAE）. The neutron flux was monitored by measuring the activity of 92mNb produced in the competing reaction channel of 93Nb（n, 2n）92mNb. At the neutron energy of 14.6 MeV, the 93Nb（n, 2n）92gNb reaction cross-section of （736±220） mb was obtained for the first time.