通过~(12)C(~(11)B,~7Li)~(16)O反应研究~(12)C(α,γ)~(16)O天体物理S_(E2)因子

正~(12)C(α,γ)~(16)O被认为是最重要的核天体物理反应之一。作为3α反应合成~(12)C后的后续反应,该反应强烈影响着宇宙中碳氧同位素(主要为~(12)C和~(16)O)的丰度比,而这两种同位素是可观测宇宙中丰度第4和第3高的同位素。本工作通过测量~(12)C(~(11)B,~7Li)~(16)O反应,导出6.917MeV 2~+阈下共振的约化α宽度,并根据约化α宽度,导出~(12)C(α,γ)~(16)O在伽莫夫窗口内的天体物理S_(E2)因子。本实验在中国原子能科学研究院的HI-13串列加速器上进行。采用束流能量为50 MeV的~(11)B束流,对~(12)C(~(11)B,~7Li)~(16)O反应~(16)O 6.917 MeV激     

恒星中子源~(13)C(α,n)~(16)O反应的研究

13 C(α,n)16 O是渐进巨星支(AGB)星中慢速中子俘获(s)过程的主中子源反应,而17 O 6.356 MeV1/2+阈下共振对13 C(α,n)16 O反应影响很大。本文使用HI-13串列加速器和Q3D磁谱仪,首次测量了13C(11B,7Li)17 O转移反应角分布,确定了影响13C(α,n)16 O反应最关键、最不确定的17 O(Ex=6.356MeV)阈下共振态的α宽度,从而得出天体物理能区13 C(α,n)16 O反应的天体物理S因子和反应率,澄清了国际上已有S因子数据间高达25倍的巨大分歧。AGB星s过程核合成网络计算表明:新反应率数据导致恒星中铅的丰度增加了25%。     

12C18O和13C16O分子X1∑+基态的完全振动能谱和同位素位移

采用双原子分子及离子体系的完全振动能谱和精确振动光谱常数的代数方法(Algebraic Method),根据实验所得的一组精确的12C16O分子X1Σ+基态低振动能级计算出其精确振动光谱常数和完全振动能谱;并结合Herzberg的同位素效应理论得出实验上缺乏的12C18O和13C16O分子X1Σ+基态的各项光谱常数,计算出它们之间的同位素位移。     

12C18O和13C16O分子X1∑+基态的完全振动能谱和同位素位移

采用双原子分子及离子体系的完全振动能谱和精确振动光谱常数的代数方法(Algebraic Method),根据实验所得的一组精确的12C16O分子X1∑+基态低振动能级计算出其精确振动光谱常数和完伞振动能谱;并结合Herzberg的同位素效应理论得出实验上缺乏的12C18O和13C16O分子X1∑+基态的各项光谱常数,计...     

流体的混合和沸腾对浅成热液矿床石英和方解石同位素组成的影响

在含金银的浅成热液脉状矿床中,热水的混合和沸腾导致溶液温度下降和溶质离子浓度的变化,被认为是这种矿床矿物沉淀的一个基本机制。根据沉淀矿物的同位素组成可以判断热水的来源、溶液的化学性质和矿物的形成温度。沸腾的热流体温度高于100℃时,热流体氧同位素的变化是不明显的。沉淀矿物的同位素组成分晶效应也小。深部热流体与低温浅成水混合,由于热水的~(13)O/~(16)O比值降低,δ~(18)O值也下降。溶液温度降低同位素分馏效应增大。尽管流体δ~(18)O值因为混合而降低,而沉淀矿物的δ~(18)O值随着温度降低而增加。从串木野矿床所见到的浅成热液矿脉矿物δ~(18)O值来看,不排除流体沸腾的可能性或流体的混合。方解石的碳同位素组成由溶液中含碳组分和温度控制。在近中性和pH值较低条件下,流体沸腾可使沉淀的方解石δ~(13)C突然增加。从串木野矿床的脉状方解石δ~(13)C值可以表明它是在pH值为6—7的条件下沉淀的。     

稳定同位素~(13)C或D标记对甲氧基苯甲酸的合成

稳定同位素标记对甲氧基苯甲酸是防腐剂、香料及药物等稳定同位素标记内标试剂合成中的重要中间体。本文以尼泊金乙酯(对羟基苯甲酸乙酯)和碘甲烷-~(13)C或碘甲烷-D3为原料,碱性条件下经2步反应合成对甲氧基苯甲酸-甲氧基-~(13)C和对甲氧基苯甲酸-甲氧基-D3。通过单因素实验确定适合的反应温度、物料摩尔比、反应时间,优化工艺参数为:反应温度为80℃,物料摩尔比n(碘甲烷-~(13)C/D3)∶n(尼泊金乙酯)=1.15∶1,反应时间为6h。产品经液质联用仪(LC-MS)测试化学纯度和同位素丰度、经核磁共振(1 H NMR)进行结构确认,对甲氧基苯甲酸-甲氧基-~(13)C的收率为91.12%,碘甲烷-~(13)C利用率为79.32%,产品熔点为186.5~187.8℃,化学纯度为99.1%,~(13)C同位素丰度为99.0%;标记对甲氧基苯甲酸-甲氧基-D3的收率为90.49%,碘甲烷-D3利用率为78.70%,产品熔点为186.3~188.1℃,化学纯度为99.0%,D同位素丰度为98.1%。     

稳定同位素~(13)C标记乙醇

以Ba13CO3为原料,采用碳化锂方法制备乙炔,再经催化水合法和NaBH4还原,制备了13C-乙醇。考察了反应温度、助催化剂等合成工艺对产物收率的影响。设计的合成路线反应条件温和,总收率高于50%。产品经红外、色谱和核磁检测,化学纯度99%,13C同位素丰度95%,产物的同位素丰度相对原料而言降低3%。     

利用稳定同位素δ~(18)O估算湖泊渗漏量

基于稳定同位素质量平衡及水量平衡,推导了内陆湖泊稳定同位素模型,结合羊卓雍错氧同位素数据计算了羊卓雍错湖水渗漏量。讨论了湿度因子、温度因子对湖泊渗漏量的影响。结果表明,在其他影响因子不变条件下,渗漏量所占比重越大,湖水δ18O值越负。羊卓雍错湖每年的渗漏量达到补给量的30.6%。     

同位素标记原儿茶酸-(~(13)COOH)的合成研究

设计了以3,4-二甲氧基溴苯为原料,经格利雅反应制备得到格式试剂,通入13 C标记的13 CO2气体,制备得中间体3,4-二甲氧基苯甲酸-(13 COOH)。将中间体用BBr3脱除甲基后得到粗产品,粗产品再经过活性炭脱色,冷却结晶得到原儿茶酸-(13 COOH)。设计的合成路线操作简单,工艺流程短,副产物少,收率可达45%,13 C同位素丰度稀释低。产物经HPLC、MS、1 H NMR和13 C NMR表征,结果表明:制备的原儿茶酸-(13 COOH)化学纯度99%,13 C同位素丰度98%,作为重要的示踪剂,可为医药和化工领域研究提供基础。     

~(130)Ce(EC+β~+)衰变研究及其放射化学分离

利用兰州SFC加速的16O束轰击同位素118Sn ,由熔合蒸发 4n反应产生目标核13 0 Ce。为了消除本底干扰并指定13 0 Ce核 ,采用溶剂萃取法对He - jet带传输系统从靶室传输出来的反应产物进行了离线分离与纯化。将目标核13 0 Ce从大量的靶材料、反应产物及母核中分离出来 ,快速制成薄源后在铅室中进行γ单谱测量及X -γ、γ -γ符合测量。从化学分离后的产物中观察到了半衰期为 2 2 .9min的 10 8条γ射线 ,其中 10 7条是新发现的 ,该活性被指定为13 0 Ce。在此基础上 ,进一步研究这些γ线的级联关系 ,建立了缺中子同位素13 0 Ce较完整的 (EC + β+ )衰变纲图。为118Sn(16O ,4n) 13 0 Ce反应体系建立的放化分离流程的分离时间仅 10min ,化学产额大于70 %。化学分离除去 98%以上的核反应生成的13 0 La ,对其它杂质的去污完全满足13 0 Ce(EC + β+ )衰变研究的要求。     

Carbon and Oxygen Isotope Separation by Plasma Chemical Reactions in Carbon Monoxide Glow Discharge

The separation of carbon and oxygen isotopes in CO glow discharge has been studied. The isotope enrichment in the products was measured by quadru-pole mass spectrometer. The reaction yield and empirical formula of solid phase products were determined by the gas-volumetric analysis. The stable products obtained in our experiment are CO₂ and solid polymers formed on the discharge wall. The polymer consists of both carbon and oxygen and the oxygen/carbon mole ratio in the polymer is 0.35±0.05. The isotope enrichment coefficients show a strong negative dependence on discharge current though the relative reaction yields have an opposite tendency. Consequently, the maximum isotope enrichment coefficients for ¹³C in wall deposit of 2.31 and for ¹⁸O in CO₂ of 1.37 are obtained when the discharge current and the reaction yields are minimum in our experimental range. The experimental results of isotope enrichment have been compared with theoretical values estimated by an analytical model of literature. The dilution mechanism of the isotope enrichment of stable products is inferred from the isotopic distributions of ¹³C and ¹⁸O in products and theoretical predictions for isotope enrichment.     

Atomic masses of the isotopes C13, N14, N15

We present the results of new mass-spcttrographic measurements of the atomic masses of C¹³, N¹⁴ and N¹⁵. We show the internal consistency for the mass values of these isotopes obtained from different sets of mass doublets. The measurements were performed under conditions climinating systematic errors. We describe the method for precision adjustment of the ion-optical system. The values obtained for the masses of C¹³, N¹⁴ and N¹⁵ are 13.007491 ± 3·10^–6 and 14.007527 ± 4·10^–6 amu and 15.004890 ± 5·10^–6 amu. which is in good agreement with the values recently published by Nier and co-workers. This data is higher than the average data obtained from nuclear reactions and by statistical analysis. The difference in the values is explained by the inexact measurement of the Q-values used in calculating the masses of the parent isotopes n_o, H. D. He⁴ and C¹², and of the isotopes C¹³, N¹⁴ and N¹⁵.In conclusion the authors express their gratitude to I.G. Gvertseteli and V.K. Tskhakaia for making available the enriched C¹³ isotope, as well as to P.S. Brostiuk and M.I. Dzkuia for practical help with the work.     

Determination of 13C/12C ratios with (d, p) nuclear reactions

Stable isotope ratios such as ¹³C/¹²C play an important role in many applications including environment and energy research. Since many surface analysis techniques are plagued with unavoidable hydrocarbon contamination issues during analysis, it is highly desirable that ¹³C and ¹²C isotopes be measured simultaneously especially in specimens with a minute amount of ¹³C, in order to reliably determine ¹³C/¹²C ratios. In this paper, we report that deuterium induced proton particle reactions, ¹³C(d, p)¹⁴C and ¹²C(d, p)¹³C, provide a convenient and reliable approach for ¹³C/¹²C ratio determination. Optimizations on experimental considerations and potential interferences from other common light isotopes are discussed as well as results from the application of this technique to diagnose the performance of a target debris collection in an inertial confinement fusion (ICF) experiment.     

5-羟色胺转运蛋白显像剂~(11)C-DASB的自动化合成及Micro PET/CT显像

目的:自动化合成5-羟色胺转运蛋白显像剂11 C-DASB并进行大鼠Micro PET/CT显像;方法:通过改变甲基化试剂、溶解前体溶剂及反应条件,得到优化的标记条件作为碳-11多功能合成模块的输入参数,进行自动化合成11 C-DASB,大鼠静脉注射11 C-DASB 45 min后进行显像;结果:采用11 C-CH3-Triflate作为甲基化试剂,通入新配制的含1mg去甲基DASB前体的500μL DMSO溶液内,80℃下加热2min,标准率为63.7%,大鼠显像表明,11 C-DASB特异性的浓聚于SERT富集区域;结论:经优化,11 C-DASB自动化合成可得到较高产率,大鼠显像表明,其特异性浓聚于SERT富集区域,有望作为5-羟色胺转运蛋白显像剂。     

Isotope Effect and Isotope Separation: A Chemist's View

The behavior of uranyl fluoride complexes containing different isotopic species [¹⁶O-U-¹⁶O]²⁺, [¹⁶O-U-¹⁸O]²⁺, [¹⁸O-U-¹⁸O]²⁺ in isopropanol solutions under UV irradiation was studied. The rate of decrease in concentration of uranyl complexes containing isotopic species [¹⁶O-U-¹⁸O]²⁺ is higher than that for uranyl containing [¹⁸O-U- ¹⁸O]²⁺ species. It was shown that this phenomenon is not caused by difference in extinction energy of vaious isotopic species.     

Room-Temperature Reactor Packed with Hydrophobic Catalysts for the Oxidation of Hydrogen Isotopes Released in a Nuclear Facility

A room-temperature reactor packed with hydrophobic catalysts for the oxidation of hydrogen isotopes released in a nuclear facility will contribute to nuclear safety. The inorganic-based hydrophobic Pt catalyst named H1P has been developed especially for efficient oxidation over a wide concentration range of hydrogen isotopes at room temperature, even in the presence of saturated water vapor. The overall reaction rate constant for hydrogen oxidation with the H1P catalyst in a flow-through system using a tritium tracer was determined as a function of space velocity, hydrogen concentration in carriers, temperature of the catalyst, and water vapor concentration in carriers. The overall reaction rate constant for the H1P catalyst in the range near room temperature was considerably larger than that for the traditionally applied Pt/Al₂O₃ catalyst. Moreover, the decrease in reaction rate for H1P in the presence of saturated water vapor was slight compared with the reaction rate in the absence of water vapor due to the excellent hydrophobic performance of H1P. Oxidation reaction on the catalyst surface is the rate-controlling step in the range near room temperature and the rate-controlling step is shifted to diffusion in a catalyst substratum above 313K due to its fine porosity. The overall reaction rate constant in the range near room temperature was dependent on the space velocity and hydrogen concentration in carriers. The overall reaction rate constants in the range of 1;000=T greater than 3.2 correlated to k _overall[s^?1] = 5.59 × 10⁷ × SV[h^?1] × exp (?67.7 [kJ/mol]/R_gT), where the space velocity range was from 600 to 7,200 h^?1.     

Irradiation damage induced on polyethylene terephtalate by 1.6 MeV deuteron ions

The irradiation damage caused on polyethylene terephtalate (Mylar, PET) samples by 1.6 MeV deuteron ions has been measured using simultaneously the nuclear reaction analysis (NRA) and the transmission energy loss (TEL) techniques. The irradiation was carried out at normal incidence relative to the target surface with the irradiation beam being used as the analysis beam. The evolution of the overall damage during irradiation was evaluated by measuring the variation of the energy loss of the deuteron beam passing through the target. For this purpose, a solid state Si detector placed at a forward angle of 30° relative to the incident beam direction was used. The NRA spectra recorded by a second Si detector located backward at 150° allowed the evaluation of the carbon and the oxygen depletion. The beam spot size was circular in shape and 1 mm in diameter and the beam current was set at 5 nA. The ion fluence was increased up to the value of 2.5 × 10¹⁶ deuterons/cm². It was observed that the target energy loss decreased steadily as the fluence increased and levelled off at high fluence. The ¹⁶O(d,p₀)¹⁷O, ¹⁶O(d,p₁)¹⁷O^* and ¹²C(d,p₀)¹³C reactions were used for monitoring the evolution of the oxygen and carbon content as a function of the deuteron fluence. A monotonic decrease of the oxygen content with the increase of ion fluence was observed. At the highest fluence the oxygen depletion reached a value of about 75%. For carbon, a weak depletion was observed at fluence ranging from 2.5 × 10¹⁵ d/cm² to 1.0 × 10¹⁶ d/cm² followed by a levelling-off with a total loss around 20%.     

γ辐照联合H_2O_2处理污泥滤液的研究

采用60 Coγ射线辐照处理污泥滤液,通过对比处理前后化学需氧量(COD)、紫外可见吸光度和浑浊度的变化,研究了辐照处理中初始pH、初始H2O2浓度和吸收剂量对污泥滤液处理效果的影响。结果表明:在相同吸收剂量和初始H2O2浓度条件下,酸性条件更利于CODCr的降低;γ辐照联合H2O2处理存在显著协同效应,吸收剂量为18.75kGy、初始H2O2浓度为2mmol/L时,污泥滤液CODcr去除率达70.4%,浑浊度下降94.9%。     

Controlling the density distribution of SiC nanocrystals for the ion beam synthesis of buried SiC layers in silicon

The depth distribution of SiC nanocrystals formed during high-dose implantation of carbon ions into silicon at conditions suitable for the ion beam synthesis of buried SiC layers in silicon is studied in this paper. For implantation temperatures of 400–600°C and dose rates of 10¹² − 10¹³ C⁺/cm²s, SiC precipitates in crystalline silicon are observed to be of approximately equal size, independent of the depth position beneath the surface. Ballistic destruction of small precipitates and difficulties in precipitate growth are thought to be responsible for the observed narrow size distribution. The destruction of precipitates may lead to the simultaneous release of a superthreshold concentration of carbon atoms resulting in a carbon-induced amorphization of the silicon host lattice. The local reduction of the number density of SiC nanocrystals involved with this amorphization can be used to tailor discontinuous depth distributions of oriented SiC precipitates providing ideal starting conditions for the synthesis of well-defined single-crystalline SiC layers in silicon.     

K X-ray emission induced by C and O ion impact on selected lanthanoids

Measurements of K-shell X-ray production cross sections by ¹²C⁴⁺ (beam energies between 12 MeV and 14 MeV), and ¹⁶O⁵⁺ ions (with energies between 12.5 MeV and 15 MeV) are presented. The target elements were selected lanthanoids (Ce, Gd, Dy, Ho and Er). The resulting measurements are evaluated through comparisons with the eECPSShsR-UA theory, the MECPSSR model and the adiabatic perturbation (also known as direct molecular orbital, MO) theory, using a scaling based on the reduced velocity parameter . Consideration is given to multiple ionization effects and electron capture contribution to K-shell ionization. An evaluation with previously published values is also given. It is shown that the behavior of the ratios of experimental to theoretical cross sections is different for both ions. The models do not seem to be accurate to predict the X-ray production cross sections for ¹²C⁴⁺ ions, while the MECPSSR theory predicts much better the experimental data for ¹⁶O⁵⁺ than the eECPSShsR-UA.