Measurement of 79Se by accelerator mass spectrometry using projectile X-ray technique

1IntroductionInacceleratormassspectrometry(AMS)measurementsoflong-livedradioisotopes,stableisobarsarethedominantbackground.FortheradioisotopesofatomicnumberZ520,theisobarsbackgroundcanbeeliminatedbymeansofthedifferentenergylossofisobarinmatterduetotherateofenergylossisafunctionofZ.Butwithincreasingatomicnumber,theenergystragglingincreasesrelativetotheenergylossdifference,sothatisobarseparationbecomesprogressivelylesseffective.Inordertoseparatetheisobarswithhigheratomicnumberstheionenergyhast…     

Isobar separation at very low energy for AMS

The separation of atomic and molecular isobars, prior to injection into a tandem accelerator for Accelerator Mass Spectrometry (AMS), is discussed. To accomplish this separation, the anions from a standard sputter ion source are retarded to eV energy. The advantages of using very low energy (eV) for this purpose are twofold. The ionic reactions in gases can be isobar specific and the multiple scattering of the eV ions, unlike that at higher energy, can be controlled in linear radio-frequency multipoles. An example of current interest to AMS practice, the suppression of the S⁻ isobar ions from negative ion sources generating mainly Cl⁻ ions, will be described. It will be argued that this is a universal method for isobar separation prior to AMS, which is applicable to atomic anions and cations as well as their molecular counterparts. This procedure should be applicable to the AMS analysis of most rare radioactive species, as atomic or molecular ions, starting with either anions or cations, with appropriate charge changing. In some cases the ions may be analysable without AMS.     

An important mechanism of crop breeding with ultralow energy ion implantation

The characteristic X-rays excited in carbon compounds of seeds by ultralow energy (110 keV) ions implanted in wheat seeds were simulated with carbon-light of synchrotron-radiation. After the seeds were irradiated with the C-light, the through-germination survival fraction of the seeds and the micronucleus frequency in their root-tip cells could be measured. The data verify that the characteristic X-rays excited by the ultralow energy ions implanted in the seeds provide an important mechanism of crop breeding.     

Background reduction for heavy element accelerator mass spectrometry

The energy distribution of negative ions generated by low energy (keV) Cs⁺ bombardment of solids has been studied over 11 decades of negative ion intensity. The higher energy component of this ion spectrum is characterized approximately by an E⁻² distribution, terminated by the kinematic limit for two-body collisions. In the case of 27 keV Cs bombardment on carbon an excess energy of 6 keV beyond the mean emission energy was observed. A more complex, low energy ion spectrum was attributed to molecular fragmentation processes within the ion extraction field and subsequent beam transport system. The elimination of these tails and other ions prior to tandem acceleration, and hence the removal of potential sources of background in accelerator mass spectrometry (AMS) are discussed in this paper, with a view to extending the detection limits in AMS for elements other than ¹⁴C and especially for heavy elements.     

AMS Measurement of ^93Zr

The zirconium isotope ^93Zr is a long-lived pure beta-particle-emitting radionuclide, which is produced by nuclear fission and neutron activation of the stable isotope ^92Zr. This element is a constituent of the structural components of nuclear reactor vessels. With AMS it should be possible to detect minute amounts of ^93Zr. A Silica gel adsorption chromatography method for radiochemical separation of Zr has been developed to reduce the stable isobar ^93Nb, which is the main interference for the detection.     

∑HfF（5,-） current monitoring with off-axis Faraday cup in AMS measurement of ^（182）Hf at CIAE

In order to reduce the systematic uncertainties caused by the sequential injection in AMS measurement of ¹⁸²Hf,a technique for instantaneous monitoring of off-axis∑HfF₅^- current was developed in the AMS laboratory at China Institute of Atomic Energy（CIAE）.The stability and reliability of this method have been experimentally verified.As a result,the accuracy for AMS measurement of¹⁸²Hf was significantly improved.     

Pu同位素的AMS测量方法研究进展

锕系超铀元素Pu主要来自于各类人工核活动,现广泛存在于自然界中.其在多个基础研究及应用领域具有重要研究和使用价值,并已得到广泛应用.本文比较了目前Pu的主要测量方法,对各种方法的优缺点加以分析.在所有Pu的测量方法中,加速器质谱(AMS)方法具有样品用量小、测量时间短、能区分239Pu与240Pu,同时探测限低等优点,...     

A new HVE 6 MV AMS system at the University of Cologne

CologneAMS is the new Centre for Accelerator Mass Spectrometry (AMS) at the University of Cologne. It will operate a dedicated AMS system designed to measure all standard cosmogenic nuclides (¹⁰Be,¹⁴C,²⁶Al,³⁶Cl, ⁴¹Ca,¹²⁹I) and which uses a 6 MV Tandetron™ accelerator equipped with an all solid-state power supply, foil and gas stripper. The system also enables a sensitive detection of heavy ions up to ²³⁹U and ²⁴⁴Pu. The high-energy mass-spectrometer consists of a 90 degree magnet with a radius of 2 m and a mass-energy product of 351 AMU MeV to allow the detection of ²⁴⁴Pu⁵⁺ up to the maximum terminal voltage of 6 MV. This magnet is followed by an electrostatic energy analyzer and a switching magnet that can transport the rare isotope beam into various beamlines. The switching magnet forms a third analyzing element which is needed especially for the sensitive detection of heavy elements. So far two beamlines are equipped with their own detection system. One of these lines is used for suppression of isobaric background in the case of the analysis of e.g. ³⁶Cl. This is accomplished by an absorber foil which generates a Z-dependent energy loss in combination with a momentum/charge-state selection via a 120 degree magnet that features up to 30 mrad acceptance for efficient beam transport.In this contribution we will introduce the new Centre, the layout and specific characteristics of the AMS system as well as the main topics of the future scientific work to be performed at CologneAMS.     

3 MV加速器质谱测量36Cl

在端电压为3 MV的AMS装置上实现³⁶Cl及其他中重核素的高灵敏测量是AMS技术发展的重要方向之一。为进一步提高充气飞行时间探测方法中³⁶S的压低能力,本文研究了³⁶S和³⁶Cl在P10、异丁烷和丙烷气体中的能量歧离和角度歧离。在32 MeV的入射能量下测量了几个地下水样品中³⁶Cl的[JP2]含量,测量结果与72 MeV能量下的测量结果相符。测量结果表明,采用充气飞行时间探测方法在3 MV的串列加速器上测量³⁶Cl时,探测限为³⁶Cl/Cl≈10^-14,当样品中³⁶Cl/Cl≈10^-13时测量不确定度为30%。     

Assessment of mouse BMMNC DNA damage with a two-tailed comet assay after X-ray and carbon ion total body irradiation

The two-tailed comet assay(2T-comet assay) is a method for simultaneously evaluating DNA single-strand breaks(SSBs) and double-strand breaks(DSBs). In the present study, the endonuclease DNase I and hydrogen peroxide were used to induce DSBs and SSBs in bone marrow mononuclear cells(BMMNCs) from mice, and the damaged DNAs were assessed with a 2T-comet assay. The results demonstrated that this method can detect and discriminate between BMMNC DNA SSBs and DSBs simultaneously. Using this method, we studied DNA damage in BMMNCs from female BALB/c mice after total body irradiation with X-rays and carbon ions. The results indicated that these two types of radiation induced serious DNA damage in BMMNCs in a dose-dependent manner.The DNA damage induced by carbon ions was more severe than that induced by X-rays at the same dose, and a high dose of carbon ion radiation was more likely to cause death in mice. The DSBs and SSBs induced by X-rays were the highest on the 3rd day post-IR. For carbon ion radiation,DSBs were the most serious on the 3rd day, while SSBs were more obvious on the 3rd day and 13th day post-IR.The ratio of DSBs/SSBs was clearly related to the different types of radiation.     

Charge state distribution studies of SrF3, MnF3 and CaF3 molecules using single and double stripping in a Tandem accelerator

High energy beams of high ion currents from a Tandem accelerator are a common requirement in nuclear physics, materials science and Accelerator Mass Spectrometry (AMS) research. In many cases, molecular beams are chosen from the ion source to achieve a high ion source yield for the negative ions, or, as for AMS, to suppress isobaric interference. For this reason we have studied the use of consecutive stripper foils, double stripping, to increase the ion yield in conjunction with increased energy of injected molecular beams through a Tandem accelerator. By this method we could achieve a shift in the yield towards higher charge states.     

重离子与X射线沿水介质入射深度诱导癌细胞失活的比较

采用Hela、B16两种细胞分别研究了X射线和重离子在水介质中入射的深度与相应细胞的存活率（1－失活率）。结果表明：X射线与重离子在入射深度与细胞存活关系上有明显不同的变化规律。X射线的入射深度与其细胞存活率呈高度正相关,r=0.92;而重离子通过路径的细胞损伤率较小、且在一个细胞存活较高的坪区（86％－92％）,到射程末端细胞损伤率剧增,出现倒Bragg峰。提示：重离子在深层肿瘤治疗上具有比X射线好的深度治疗分布。     

Isobaric identification techniques of AMS at CIAE

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.     

Applications of a compact ionization chamber in AMS at energies below 1 MeV/amu

The increasing demand for measuring long-lived radionuclides with small AMS machines at energies below 1 MeV per nucleon raises the need for compact detectors which still have a decent energy resolution and allow for a clear identification of the incident particles. Based on a design by the AMS group at the ETH Zurich a compact gas ionization chamber was built and installed at the 3 MV tandem AMS facility VERA (Vienna Environmental Research Accelerator). The main challenge in AMS is the detection of rare isotope species in the presence of strong isotopic and isobaric interferences. The task of the ionization chamber is the suppression of the unwanted isobar by separating the ions via their different stopping powers. Measurements of ³⁶Cl at VERA showed an achieved suppression of the unwanted stable isobar ³⁶S of 3 × 10⁻⁴ and measurements of ¹⁰Be showed an achieved suppression of ¹⁰B of at least 3 × 10⁻⁶. Additional suppression of the isobaric ions can be achieved by a degrader foil technique applied to ¹⁰Be measurements by G.M. Raisbeck. In combination with the new ionization chamber the achieved suppression of ¹⁰B is at least 10⁻¹⁰. Measurements of blank samples at VERA show that the background for AMS with ¹⁰Be is below 2 × 10⁻¹⁵.     

Applications of accelerator mass spectrometry to electronic materials

Applications of accelerator mass spectrometry (AMS) to stable-element detection in electronic materials are being explored. Conventional AMS hardware at the University of Arizona has been used to profile shallow semiconductor structures (ion-implanted samples) and to establish minimum values of system efficiency for several ions in Si and/or GaAs. A custom instrument under development at the University of North Texas has been used to generate molecule free mass spectra which can be directly compared with secondary-ion mass spectrometry (SIMS) data. Elemental fragments associated with molecular dissociation after passage through the accelerator are shown to constitute a source of system “background” which can be removed through clever selection of charge states.     

Investigation of metal matrix systems for cosmogenic Al analysis by accelerator mass spectrometry

We report experiments designed to help optimize accelerator mass spectrometry (AMS) of ²⁶Al (in the form of Al₂O₃) for geochronologic and geomorphologic applications. Analysis times are long and the precision of AMS are restricted by counting statistics for ²⁶Al, which are in turn limited by the intensity of Al⁻ beam currents. We show that ion beam currents are affected by the metal matrix in which Al₂O₃ is dispersed, by the matrix-to-Al₂O₃ mixing ratio, and for at least some matrices, such as Ag, by the depth to which the sample is packed in the AMS cathode. Typical instantaneous Al⁺⁷ currents (μA) produced by the LLNL CAMS Cs sputter ion source and measured in a Faraday cup after the accelerator are 2.26 for samples in Ag, 2.17 in Re, 2.00 in Nb, 1.92 in V and 1.73 in Mo. The AMS counting efficiency (Al⁻ ions detected per Al atom loaded in the target) for a constant analysis time (900 s) and for equimolar mixtures of Al₂O₃ and matrix is in the range of 6 × 10⁻⁵–9 × 10⁻⁵ in the order Ag > Re > Nb > V > Mo. Additionally, we observed a correlation between the ion detection efficiency (Al ions detected per Al atoms loaded) and the matrix work function and inverse vaporization enthalpy of the matrix and beam current. Typical currents (μA) obtained with elemental Al are 13.3 for samples in no matrix, 3.23 in V, 3.14 in Nb, 3.07 in Re, 2.85 in Mo, 1.46 in Ag. The ion detection efficiency for elemental Al correlates strongly with matrix electron affinity. Thus, our data indicate that the current practice of mixing Al₂O₃ with Ag is reasonable until a means is found to produce cathodes of elemental Al.     

External scanning micro-PIXE for the characterization of a polycapillary lens: Measurement of the collected X-ray intensity distribution

We developed a PIXE detection system for the analysis of medium-light elements which exploits a weakly focusing polycapillary lens for the transmission of the X-rays emitted from the target material to a Silicon Drift Detector. The polycapillary lens efficiently collects X-rays, while prevents back-scattered protons from impinging on the detector chip, thus avoiding electronics perturbation and consequent quality loss of PIXE spectra. The system is optimized for the detection of X-rays in the energy range 1–10 keV, when the emission from the target is induced by MeV proton beams with size of the order of a few hundreds of micrometers.This work reports the results of the lens characterization in terms of X-ray collection spot, i.e. the area of the sample actually “seen” by the lens, and its dependence on the X-ray energy. The lens properties have been measured using the external scanning microbeam facility of the Tandetron accelerator at LABEC-INFN in Florence. The detection system was used to detect X-rays from a set of pure elemental standards with an incident 3 MeV proton beam focused to a size of about 30 μm scanning an area of 1.9 × 1.6 mm². By measuring the spatial distribution of characteristic X-rays from each given material, the collection profile of the lens at the corresponding X-ray energy was obtained. Using several standards, the behaviour throughout the range 1–10 keV was examined. The sensitivity of the lens collection profile on the lens-sample out-of-focus distance was also investigated.     

特征X射线能谱法测定Fe^＋注入小麦种子的深度

用１１０ｋｅＶ Ｆｅ＾＋离子束垂直注入小麦种胚后，在扫描电子显微镜上沿种子纵沟剖面，在不同深度上测量Ｆｅ元素被激发出的特征Ｘ射线强度分布，结果表明分布呈指数衰减，与晶体中的热扩散分布相类似，并对此进行了讨论。     

用于高灵敏度AMS10Be测量的气体探测器

¹⁰Be是加速器质谱（AMS）测量中重要性仅次于¹⁴C的核素,在第四纪地质研究等方面发挥着重要作用。为更好地开展岩石暴露年龄测定和黄土中¹⁰Be浓度测量等应用研究,北京大学加速器质谱（PKUAMS）在深入研究离子鉴别物理过程的基础上,设计研制了1台气体探测器,¹⁰Be高能端测量效率达90%以上,¹⁰Be粒子计数率明显增加。在离子源引出只有1.2μA（最大值可达2μA）的情况下,标准样品NIST的¹⁰Be粒子计数率已达23s^-1。