基于SnF2靶样的加速器质谱测量裂变产物126Sn的方法研究

在中国原子能科学研究院HI-13串列加速器质谱系统上建立了以SnF₂为靶样,引出SnF₃^-分子负离子形式的¹²⁶Sn-AMS分析方法。介绍了用于AMS测量的¹²⁶Sn实验室参考标准的研制以及靶物质SnF₂的化学制备过程,通过引束实验确定了可将同量异位素¹²⁶Te本底干扰压低2～3个量级的SnF₃^-分子负离子引出形式,实现了¹²⁶Sn束流的传输以及同量异位素的探测和鉴别。对制备的3个标准样品（¹²⁶Sn/Sn原子个数比为1.033×10^-8、4.54×10^-9、6.43×10^-10）的测量结果显示,¹²⁶Sn/Sn原子个数比测量值与标称值呈良好的线性关系（R²=0.999）,通过测量空白样品获得系统探测¹²⁶Sn测量的灵敏度为（1.92±1.13）×10^-10。     

182Hf的AMS测量技术研究

为实现对¹⁸²Hf岩石样品的AMS精确测量,基于HI-13串列加速器对测量技术和方法等进行了系统的改进,主要包括：¹⁸²Hf空白样品的制备、偏置束流的同时监测技术、加速器系统稳定性检验、交替测量方案的实施、¹⁸²W扣除方法的改进、模拟样品测量检验、岩石样品测量检验及测量结果可信度检验等。实验结果表明,对于1×10^-10(¹⁸²Hf/¹⁸⁰Hf)水平的模拟样品,测量结果的相对不确定度约为12%,基本达到岩石样品的测量要求。岩石样品的测量不确定度较大,主要原因是岩石样品中W的含量较高。     

Recent advances in AMS of Cl with a 3-MV-tandem

Accelerator mass spectrometry (AMS) of ³⁶Cl (t_1/2 = 0.30 Ma) at natural isotopic concentrations requires high particle energies for the separation from the stable isobar ³⁶S and was so far the exclusive domain of tandem accelerators with at least 5 MV terminal voltage. Using terminal foil stripping and a detection setup consisting of a split-anode ionization chamber and an additional energy signal from a silicon strip detector, a ³⁶S suppression of >10⁴ at 3 MV terminal voltage was achieved. To further increase the ³⁶S suppression energy loss straggling in various counter gases (C₄H₁₀, Ar-CH₄ and C₄H₁₀-Ar) and the effect of “energy focusing” below the maximum of the Bragg curve was investigated. The comparison of experimental data with simulations and published data yielded interesting insights into the physics underlying the detectors. Energy loss, energy straggling and angular scattering determine the ³⁶S suppression. In addition, we improved ion source conditions, target backing materials and the cathode design with respect to sulfur output and cross contamination. These changes allow higher currents during measurement (³⁵Cl⁻ current ≈ 5 μA) and also increased the reproducibility. An injector to detector efficiency for ³⁶Cl ions of 8% (16% stripping yield for the 7+ charge state in the accelerator, 50% ³⁶Cl detection efficiency) was achieved, which can favorably be compared to other facilities. The memory effect in our ion source was also thoroughly investigated. Currently our measured blank value is ³⁶Cl/Cl ≈ 3 × 10⁻¹⁵ when samples with a ratio of 10⁻¹¹ are used in the same sample wheel and ³⁶Cl/Cl ≈ 5 × 10⁻¹⁶ if measured together with samples with a ratio of 10⁻¹² or below. This is in good agreement with the lowest so far published isotope ratios around 5 × 10⁻¹⁶ and demonstrates that 3 MV tandems can achieve the same sensitivity for ³⁶Cl as larger machines.     

Experimental study of the excitation functions of deuteron induced reactions on Sn up to 40 MeV

Using the stacked-foil activation technique, cross-sections of deuteron induced reactions on natural Sn were measured up to 40 MeV. Excitation functions are reported for the product nuclides ¹¹¹In, ¹¹³Sn, ^117mSn, ^125mSn, ^125gSn, ¹¹⁵Sb, ^116mSb, ¹¹⁷Sb, ^118mSb ^120mSb, ¹²²Sb, ¹²⁴Sb and ¹²⁵Sb and compared with the earlier published data sets. For all excitation functions comparisons with theoretical calculations using the ALICE-IPPE, EMPIRE, EAF and the TALYS codes were performed.     

Effect analysis of the intentional depressurization on fission product behavior during TMLB' severe accident

It has been found that the pressure in the reactor coolant system (RCS) remains high in some severe accident sequences at the time of reactor vessel failure, with the risk of causing direct containment heating (DCH).Intentional depressurization is an effective accident management strategy to prevent DCH or to mitigate its consequences. Fission product behavior is affected by intentional depressurization, especially for inert gas and volatile fission product. Because the pressurizer power-operated relief valves (PORVs) are latched open, fission product will transport into the containment directly. This may cause larger radiological consequences in containment before reactor vessel failure. Four cases are selected, including the TMLB' base case and the opening one, two and three pressurizer PORVs. The results show that inert gas transports into containment more quickly when opening one and two PORVs,but more slowly when opening three PORVs; more volatile fission product deposit in containment and less in reactor coolant system (RCS) for intentional depressurization cases. When opening one PORV, the phenomenon of revaporization is strong in the RCS.     

Isotope dilution inductively coupled plasma mass spectrometry for determination of 126Sn content in spent nuclear fuel sample

The ¹²⁶Sn content in a spent nuclear fuel solution was determined by isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) for its inventory estimation in high-level radioactive waste. A well-characterized irradiated UO₂ fuel sample dissolved in a hot cell was used as a sample to evaluate the reliability of the methodology. Prior to the ICP-MS measurement, Sn was separated from Te (¹²⁶Te), which causes major isobaric interference in the determination of ¹²⁶Sn content, along with highly radioactive coexisting elements, such as Sr (⁹⁰Sr), Y (⁹⁰Y), Cs (¹³⁷Cs) and Ba (^137m Ba), using an anion-exchange column. The absence of counts attributed to Te at m/z = 125, 128, and 130 in the Sn-containing effluent (Sn fraction) indicates that Te was completely removed from the anion-exchange column. After washing, Sn retained on the column was readily eluted with 1 M HNO₃ accompanied with approximately 80% of the Cd and 0.03% of the U in the initial sample. Owing to the presences of Cd and U in Sn fraction, the measurements of ¹¹⁶Sn and ¹¹⁹Sn were affected by the isobaric ¹¹⁶Cd and the doubly charged ²³⁸U²⁺ion, resulting in the positive bias of the determined values. With the exception of the isotopic ratios including ¹¹⁶Sn and ¹¹⁹Sn, ¹¹⁷Sn/¹²⁶Sn, ¹¹⁸Sn/¹²⁶Sn, ¹²⁰Sn/¹²⁶Sn, ¹²²Sn/¹²⁶Sn and ¹²⁴Sn/¹²⁶Sn were successfully determined and showed good agreement with those obtained through ORIGEN2 calculations. The measured concentration of ¹²⁶Sn in the spent nuclear fuel sample solution was 0.74 ± 0.14 ng/g, which corresponds to 23.0 ± 4.5 ng per gram of the irradiated UO₂ fuel (excluding the presence of ¹²⁶Sn in the insoluble residue). The results reported in this paper are the first experimental values of ¹²⁶Sn content and isotope ratios in the spent nuclear fuel solution originating in spent nuclear fuel irradiated at a nuclear power plant in Japan.     

Positive ion AMS with a single-stage accelerator and an RF-plasma ion source at SUERC

The new single-stage accelerator mass spectrometer at SUERC can also accept positive ions. Potential benefits of positive ion measurement with suitable ion sources are more convenient sample form, smaller sample size, a variety of available charge states and maybe new applications. We have begun with oxygen isotope analyses to demonstrate destruction of interfering molecules.     

Radioactivity of fission product and heavy nuclides deposited on soil in Fukushima Dai-Ichi Nuclear Power Plant accident

Based on periodically performed radioactivity measurements on soil samples in the site of Fukushima Dai-Ichi Nuclear Power Station, activity ratios to ¹³⁷Cs of fission product and heavy nuclides were obtained for Sr, Nb, Mo, Tc, Ru, Ag, Te, I, Ba, La, Pu, Am, and Cm isotopes. By exponentially fitting or averaging, the activity ratios at the core shutdown were estimated. Using correlations of activity ratios of ¹³⁴Cs to ¹³⁷Cs, and ²³⁸Pu to the sum of ²³⁹Pu and ²⁴⁰Pu against fuel burnup, burnup of the fuel sourcing the deposited activity of the soil was estimated. The activity ratios to ¹³⁷Cs of each nuclide on the deposited activity were divided by those calculated on the fuel at the shutdown to obtain the deposited activity fraction of each nuclide as a relative value to ¹³⁷Cs, which also corresponds to the deposited fraction of each element as a relative value to Cs. The obtained deposited fractions relative to Cs are the orders of 10^?4 to 10^?2 for Sr, 10^?5 to 10^?3 for Nb, 10^?2 to 10^?1 for Mo, 1 to 10 for I, 10^?3 to 10^?2 for Ba, 10^?2 for La, 10^?6 to 10^?3 for Pu, 10^?6 to 10^?4 for Am, and 10^?7 to 10^?5 for Cm. The deposited fractions for Tc, Ag, and Te were not estimated due to the lack of the calculated inventories in the fuel for the relevant measured radioactive nuclides.     

14.8 MeV中子诱发~(238)U裂变产物产额测量

裂变产物产额作为裂变过程的一个重要参数,其准确测量对有关裂变的很多方面都有重要意义。为了准确测量中子诱发~(238)U裂变产物产额,利用中国工程物理研究院PD-300加速器上的T(d,n)4He反应,产生14.8MeV的中子,诱发~(238)U裂变。辐照过程中,通过金硅面垒半导体探测器监测中子通量的变化。使用Al片作为监测片计算整个照射过程中样品的平均中子通量。辐照结束后,利用高纯锗(High-Purity Germanium,HPGe)探测器测得裂变产物特征γ射线计数,计算得到裂变产物的产额,使用MCNPX软件对中子的多次散射和自屏蔽效应进行修正,并通过计算得到样品和监测片的自吸收修正、中子通量波动因子。得到了95Zr、127Sb、140Ba、147Nd、131I、103Ru等长半衰期产物的累积产额值,并将结果与以前的文献值做了比对,研究结果有助于~(238)U裂变产物产额的分析和评价。     

我国核电站长寿命裂变产物及超铀核素累积量预测

根据我国能源需求和核电发展状况的研究结果。对未来50年核电总体装机容量和乏燃料增长趋势进行了预测,对乏燃料中次量锕系核素、钚和几种长寿命裂变产物进行了计算,获得了累积量的预测数据。     

79Se的AMS测量方法研究

测定⁷⁹Se时由于⁷⁹Se尚无标准样品,需要建立⁷⁹Se/Se（⁷⁹Se、Se原子个数比,余同）的AMS测量方法。在⁷⁹Se/Se的绝对测定中,为尽可能避免测量Se的同位素之间的差异,通常利用探测器测量⁷⁹Se离子,本文用法拉第筒对⁷⁸Se和⁸⁰Se进行测量,但这造成两个测量系统之间的系统误差。为避免这种系统误差,利用同一探测器测定⁷⁹Se、⁷⁸Se和⁸⁰Se。考虑到⁷⁸Se和⁸⁰Se的计数率非常高,在CIAE-AMS系统中的静电分析器前和靶室内安装衰减片以降低⁷⁸Se和⁸⁰Se的计数率。实验结果表明：通过两个衰减片的衰减作用,能将⁷⁸Se和⁸⁰Se的束流降低到半导体探测器的检测范围内,实现了样品中⁷⁹Se/Se的绝对测定,得到⁷⁹Se/Se为(2.08±0.10)×10^-7,为准确测定⁷⁹Se半衰期奠定了基础。     

~(147)Pm对小鼠生殖细胞的遗传毒理效应

本文研究观察了小鼠静脉摄入重核裂变产物~(147)Pm后不同间隔时间对生殖细胞染色体畸变和精子(主要是无钩精子)畸形的诱变效应,实验结果发现~(147)Pm可诱发精原细胞染色体结构畸变;随着机体受内污染时间的延长,染色体畸变率和多倍体细胞也有所增加,同时~(147)Pm也可诱发初级精母细胞产生染色体断片和易位,形成多价体。染色体断片率随~(147)Pm辐照时间的延长而升高。而多价体只在内污染10天后的实验组中出现。     

First-principle studies of radioactive fission productions Cs/Sr/Ag/I adsorption on chrome-molybdenum steel in Chinese 200 MW HTR-PM

Chrome-molybdenum steel(2·1/4Cr1Mo) is one of the main products of steam generation.The adsorption behaviors of radioactive fission products on2·1/4Cr1Mo surface are critical in the analysis of HTR-PM.Here,the adsorption behavior of cesium,strontium,silver and iodine on 2·1/4Cr1Mo was investigated with first-principle calculations that the Ag and I atoms prefer to be adsorbed at the square hollow site of the face-centered cubic iron cell with a binding energy of about 1 and 3 eV,respectively.In contrast,Cs and Sr atoms are not adsorbed on the surface of the 2·1/4Cr1Mo.These results are again confirmed via analysis of charge density differences and the densities of state.Furthermore,the adsorption rates of these fission products show that only I and Ag have significant adsorption on the metal substrate.These adsorption results explain the amount of adsorbed radionuclides for an evaluation of nuclear safety in HTR-PM.These micro-pictures of the interaction between fission products and materials are a new and useful way to analyze the source term.     

Al_2O_3样品制备技术及~(26)Al的AMS测量

报道了用于加速器质谱计2 6 Al分析的Al2 O3的制备流程及2 6 Al的测量过程。制备的空白样品2 6 Al/ 2 7Al比值 <10 - 13,显示出同量异位素2 6 Mg干扰小。制备流程是成功的。     

Study of fission cross sections induced by nucleons and pions using the cascade-exciton model CEM95

Nucleon and pion-induced fission cross sections at intermediate and at higher energies are important in current nuclear applications, such as accelerator driven systems (ADS), in medicine and for effects on electronics. In the present work, microscopic fission cross sections induced by nucleons and pions are calculated on a few important targets using the cascade-exciton model code CEM95 at various energies. A change of the ratio of the level density parameter in fission to neutron emission channels is taken into account with the change in the incident energy of the projectile. The computed cross sections indicate a good agreement when are compared with the experimental values found in the literature.     

严重事故下裂变产物气溶胶自然沉积现象研究

以600 MW压水堆核电厂为研究对象,在一体化安全分析模型的基础上建立重力沉降、扩散电泳、惯性碰撞和热电泳4种裂变产物气溶胶的自然沉积模型,选取典型的严重事故序列,分析严重事故下裂变产物气溶胶的自然沉积现象。将MELCOR程序的重力沉降模型植入本文的一体化分析模型,对重力沉降份额进行比较。研究表明,重力沉降对气溶胶沉积的贡献最大;本文采用的重力沉降模型比MELCOR程序重力沉降模型的沉降效应稍强。     

Study of Al measurement on the Shanghai Mini-cyclotron based AMS

We present a modification to the ¹⁴C-dedicated SMCAMS (Shanghai mini-cyclotron based AMS) system to allow the measurement of ²⁶Al for biomedical applications with the existing devices. This is accomplished by determining the turn number, harmonic number and RF frequency theoretically and then making the appropriate orbit programming and beam optics calculation and experimental adjustments. The tests were conducted using pencil graphite (for the carbon pilot beam), Al₂O₃ powder and metal aluminum to accelerate ions with mass number of 24, 25, 26 and 27. The frequency response curves for those ions are shown. Finally, the Al₂O₃ standard sample with a known isotope ratio of 1.0 × 10⁻¹⁰ is measured. The ²⁶Al⁻ ions are detected and its frequency response curve shows the peak of ²⁶Al⁻ though very weak is well separated from the most neighboring interfering molecular ions ²⁵MgH⁻.