~(204)TI在几种金属和非金属表面上的释放行为研究

作为快速化学分离技术的基础研究,我们测定了~(204)T1在Cu、Ag、Au、Zr、Ti、Ta、Mo、Pd、Ni和不锈钢等金属表面以及SiO_2、石墨等非金属表面上的释放行为。并用理论计算的吸附焓来解释实验结果,以便对T1的吸附和解吸行为有一个进一步的了解。实验结果如下:     

俄美科学家合成新化学元素:115与113号元素

【新华网华盛顿2月1日电】俄罗斯和美国科学家宣布新合成了元素周期表上空缺的第115号和第113号元素,但一些专家表示,该成果还需进一步研究确认。据2004年2月1日出版的美国《纽约时报》报道,俄罗斯杜布纳核联合研究所和美国劳伦斯利弗莫尔国家实验室科学家共同取得的这一成果,已在新一期《物理评论C》杂志上发表。科学家们在利用回旋加速器进行的实验中,用含20个质子的钙元素的同位素反复轰击含95个质子的镅元素,结果4次成功制成第115号元素原子。这4个原子在生成数微秒后衰变成第113号元素,后者存在约1.2秒后,进一步衰变成元素周期表上的…     

卡林型金矿床中的铊

卡林型金矿床的铊和铷的可靠数据是很少发表的。过去公认的金的指示元素是As,Sb及Hg,但在某些情况下这些元素的迁移能力和金不同,故不一定总能提供确切的潜在靶区位置,而它们大多和硫化物共生。当前,在金、银、铀、铜-钼及钼矿床中,对Tl及Tl和Rb,K,Ba,Sr的关系研究表明,高的Tl含量,低的K/Tl及Ba/Tl比值以及高的Tl/Sr比值是热液成因矿床的潜在指示。然而,直到现在为止这些关系还没扩展到卡林型矿床。本文主要内容是处理在这些矿床上取得的Tl和Rb的含量数据,验证Tl,Rb以及K之间的关系作为一种找矿方法的实用性,以及对矿化和非矿化岩石中K/Rb,K/Tl,Rb/Sr及Tl/Sr比值的数据进行比较。一些作者已经提出,K/Rb及Rb/Sr比值在确定不同矿床类型中是有用的。卡林型矿床研究包括内华达的卡林、Alligator Ridge及Jerritt Canyon矿床,犹他州的Mercur矿床及蒙大拿州的北Mocasin矿床。     

氯化亚铊(~(201)Tl)放射化学纯度测定方法的选择

本文以同一批氯化亚铊和氯化铊为供试品,采用醋酸纤维薄膜电泳、纸电泳、预饱和纸层析及非饱和纸层析等不同方法进行比较,发现上述方法均能将供试品中的铊~(201)Tl(Ⅰ)和铊~(201)Tl(Ⅲ)分离。以氯化亚铊(~(201)Tl)作供试品时,测得~(201)Tl(Ⅰ)数值接近;以氯化铊(~(201)Tl)作供试品时,四种方法测定的~(201)Tl(Ⅲ)的结果很不一致。采用Na_2HPO_:丙铜=10:90为展开剂,预饱和上行纸层析的方法,能有效地测出供试品中~(201)Tl(Ⅲ),误差小,重复性好。为此,推荐上述方法为氯化亚铊(~(201)Tl)放射化学纯度测定方法     

CsI(Tl)探测器对带电粒子能量响应的入射位置依赖关系

在放射性核束物理的实验研究中,通常采用CsI(Tl)探测器对反应产物中的带电粒子进行总能量测量.使用GEANT4软件对CsI(Tl)闪烁体探测器能量响应通进行了蒙特卡罗模拟,在考虑了晶体外表面包覆材料反射率、耦合光敏二极管面积、射程等影响因素后,重点研究了CsI(Tl)闪烁体探测器对带电粒子能量响应的入射位置依赖关系....     

中日科学家成功合成第113号元素

[《科技日报》2004年9月29日报道)]日本理化研究所2004年9月28日宣布,由该所科学家和中国科学院兰州近代物理研究所、中国科学院高能研究所科学家组成的研究小组已成功合成第113号新元素。该元素是目前已知所有元素中最重的新元素。     

8×8单元CsI(Tl)探测阵列研制

描述了1个8×8单元CsI(Tl)探测阵列的结构和工作原理。探测阵列的每个单元是由1块前表面21 mm×21 mm、后表面23.1 mm×23.1 mm、高50 mm的CsI(Tl)棱台、1块光导和光电倍增管组成。在兰州放射性次级束流线(RIBLL)上对探测阵列进行测试,得到探测阵列对30 MeV质子的能量分辨可达2.7%,对170 MeV7Be可达1.5%,可很好地用于放射性束物理实验中带电粒子的鉴别。     

~(201)TlCl放射化学纯度测定方法的选择

本文以同一批一价~(201)Tl和三价~(201)Tl为供试品,采用醋酸纤维薄膜电泳、纸电泳、预饱和层析及非饱和层析等不同方法进行比较,发现上述方法均能将氯化铊中一价铊和三价铊分离,且当~(201)Tl中含少量三价铊时,测得一价供试品中一价铊(~(201)Tl)分别为99.92％(CV0.06％)、99.75％(CV0.02％)、99.87％(CV0.09％)和99.84％(CV0.09％),数值接近。但是,当以三价铊(~(201)Tl)作为供试品时,各方法测得的三价铊(~(201)Tl)含量分别为26.83％(CV29.82％)、19.06％(CV40.69％)、90.88％(CV0.53％)和15.65％(CV35.90％)。实验表明,四个方法测定三价铊的结果很不一致。采用Na_2HPO_4-丙酮(10:90)为溶剂、并在层析前预饱和15分钟、再上行层析的方法,能有效地测出供试品中三价~(201)Tl,而且误差小、重复性理想。为此,上述方法作为~(201)TlCl放射化学纯度的测定方法是适宜的。     

医用γ核素活度能谱测定法

此法全部采用国产核仪器,用Nal(Tl)探头,配FH-427型256道或FH-419型512道谱仪。具有测量可靠,计算简单,操作方便,容易掌握,可测核素多等特点。此方法的建立,解决了医用核素~(51)Cr、~(99m)Tc、~(113)Sn-~(113)mIn、~(125)I、~(131)Cs、~(133)Xe等纯γ放射性核素活度的定量测定,测量准确度在±3％—±5%之内,是一种定量测定γ放射性核素活度的好方法。     

强脉冲离子注入中的脉冲能量效应研究

在脉冲离子束流密度为15120A/cm2、脉宽为50150ns、加速电压为150260kV范围内,在11014cm-2的低注量水平上, 研究了高功率Cn++H+混合离子束注入45号钢样品的强脉冲能量效应。摩擦磨损和微观硬度测量以及SEM和X射线衍射分析表明,上述低注量强脉冲离子束注入可以改变材料 表面的微观结构和力学特性,而且强烈依赖于单个脉冲离子束的功率密度和能量密度。在相同离子注量条件下,普通C++H+离子注入对45号钢样品表面微硬度和摩擦系数未 见明显影响。直接证明了强脉冲能量效应在离子注入中是相对独立于注入元素掺杂效应的又一可利用的重要效应。基于一维导热模型,讨论了强脉冲能量效应以及脉冲离 子束功率密度对离子束材料表面改性的作用。     

用气相等温色谱和热色谱方法测定T1的氧化物的吸附焓

用等温色谱和热色谱方法分别在氢气、氩气和空气载气下测定了~(204)T1的吸附焓,并与理论和经验值进行了比较。由于在三种载气下T1的化学状态不同,本工作认为实验测得的是Tl_2O_3、TlO和Tl_2O_4的吸附焓。     

A critical examination of the thermodynamics of water adsorption on actinide oxide surfaces

The reversible adsorption of water from actinide oxide surfaces is examined from several viewpoints in this article. A reinterpretation and critical look at the previously published thermodynamic values for desorption of water from PuO₂ [J. Phys. Chem. 77 (1973) 581] are reexamined in light of more recent mathematical treatments of thermal desorption data from high surface area materials. In addition, the time and temperature dependent process of water adsorption/desorption in closed system experiments is examined using chemical kinetics modeling. A simple experimental method and mathematical treatment of determining adsorption enthalpies based upon a closed system is also described. The desorption enthalpy for reversibly adsorbed water from PuO₂ is determined to be a function of adsorbate coverage with values ranging from 51 to 44 kJ mol⁻¹ for coverages of one to several monolayers (MLs). Consistent desorption enthalpy values are obtained using either approach thus highlighting the importance of proper interpretation of adsorption parameters determined from high surface area powders. Reversible adsorption/desorption equilibrium of water with actinide oxide materials is discussed from the practical standpoint of storage and subsequent pressurization of containers. These results obtained from PuO₂ surfaces are consistent with desorption enthalpies of water from a low surface area UO₂ that has been measured using ultra-high vacuum thermal desorption mass spectroscopy to be 42.2 kJ mol⁻¹.     

Application of a Chemical ion Exchange Model to Transport Cask Surface Decontamination

Abstract

Radionuclide contamination of stainless steel surfaces occurs during submersion in a spent fuel storage pool. Subsequent release or desorption of these contaminants from a nuclear fuel transportation cask surface under varying environmental conditions occasionally results in the phenomenon known as contamination ‘weeping’. Experiments have been conducted to determine the applicability of a chemical ion exchange model to characterise the problem of cask contamination and release. Surface charge characteristics of Cr₂O₃ and stainless steel (304) powders have been measured to determine the potential for ion exchange at metal oxide-aqueous interfaces. The solubility of Co and Cs electrolytes at varying pH and the adsorption characteristics of these ions on Cr₂O₃ and stainless steel powders in aqueous slurries have been studied. Experiments show that Co ions do reversibly adsorb on these powder surfaces and, more specifically, that adsorption occurs in the nominal pH range (pH=4–6) of a boric acid moderated spent fuel pool. Desorption has been demonstrated to occur at pH≤3. Cs⁺ ions also have been shown to have an affinity for these surfaces although the reversibility of Cs⁺ bonding by H⁺ ion exchange has not been fully demonstrated. These results have significant implications for effective decontamination and coating processes used on nuclear fuel transportation casks.     

Characterization of atom and ion-induced “internal” electron emission by thin film tunnel junctions

Highly excited charge carriers are released when single or multiply charged ions impinge on metal surfaces. While electron emission into the adjacent vacuum phase is well investigated, one has only limited knowledge about the transport of excited electrons or holes into the bulk of a metal. This shortcoming can be reduced by studying the transport of these excited carriers over buried tunnel barriers in thin film metal-insulator-metal devices. The internal barriers can be tuned by a tunnel voltage which makes the device to a balance for excited electrons and holes. With a simple theoretical model we derive the balance function of different tunnel barriers and show their feasibility for the characterization of particle induced electronic excitations on metal surfaces.     

A review of corrosion product transport and radiation field buildup in boiling water reactors

Cobalt-60 is the major radiation source in the boiling water reactor (BWR) for personnel exposure during shutdown maintenance. The Co-60 activity is produced by neutron activation of cobalt with other corrosion products deposit on fuel surfaces, and is released into the coolant and deposited on primary system piping walls in the system. The transport phenomena of corrosion products in the primary system and radiation field buildup are reviewed separately in three different areas: the behavior of corrosion products in the BWR coolant, including the chemistry of corrosion products and formation of mixed metal oxides; the transport of corrosion products on fuel cladding surfaces, and the mechanisms of deposition and release are discussed; and the transport of Co-60 and radiation field buildup on out-of-core surfaces under various chemistry conditions, including normal water chemistry, hydrogen water chemistry and with chemical additives. It is concluded that with understanding the mechanisms of transport, the radiation field buildup in most operating BWRs has been considerably reduced in recent years. The major factors are reduction of cobalt source reduction, control of Co-60 release from fuel surfaces with zinc addition and improvement in water quality to minimize the corrosion product input and the material corrosion.     

Interaction of self-interstitials with solutes

For a series of solutes in Cu the enthalpy changes of solute self-interstitial binding are derived from isochronal resistivity recovery data of stage II. For solutes in Al reliable conclusions on binding enthalpies can be deduced only from resistivity damage rate measurements. For Cu as solvent both binding enthalpies and spatial ranges of solute interstitial interaction are in fair agreement with theoretical predictions. For Al both quantities are larger by a factor of about ten in experiment than in theory. For other metals various difficulties prevent an evaluation of binding enthalpies.Rutherford backscattering and Mössbauer studies are sensitive to the configuration of solute self-interstitial pairs. From vanishing of detectable configurations upon isochronal annealing binding enthalpies can be derived. The results reported thus far are generally in agreement with the above resistivity results.Field ion microscopy is discussed as a direct observation method for self-interstitials which escaped solute traps and arrived at the tip surface via long range migration.     

On the release and ionization efficiency of catcher-ion-source systems in isotope separation on-line

It is shown that the critical steps in isotope separation on-line - diffusion, effusion, and ionization - can be studied in a very efficient way by stimulating the separation process using beam particles of the UNILAC accelerator as tracer instead of reaction products. The analysis of the measured release profiles readily yields the ionization efficiency and the half-life dependence of the separation efficiency on an absolute scale. For the cases in which surface desorption is a fast process compared to solid state diffusion, additionally the decisive delay parameters μ₀ for diffusion and ν for effusion can be extracted. These are closely related to material constants such as diffusion coefficients and enthalpies for surface adsorption and in favourable cases permit extraction of the Arrhenius coefficients. Thus the assumed release model can be tested by comparison with literature values or, in turn, enables the conversion of known material constants into estimates for the half-life dependence of the separation efficiency.

Since ion sources have reached a high degree of sophistication, the ionization efficiency is hardly ever the limiting factor of on-line mass separation. This is in general also true for the diffusion step, if the distribution of the reaction products in the catcher is either homogeneous or very close to the surface. As a consequence it turns out that effusion decisively causes the limitations in mass separation on-line, i.e. surface adsorption for refractory elements and the intrinsic delay for very short half-lives.     

海藻吸附水中铀离子初步研究

在不同pH、不同铀离子浓度、不同温度及添加其他金属离子的铀溶液中，对铀离子在海藻上的吸附效率进行初步研究，同时考察溶液中一些共存金属离子对海藻吸附铀离子效率的影响。研究结果表明：pH为5～8时，烟台红藻和海菠菜受pH影响较小，吸附容量约为1.40μg/g；海木耳吸附能力受pH影响较大，吸附容量在1.03～2.23μg/g范围内波动；海藻的吸附效率及吸附容量与铀离子浓度有关，最大分别达到95.8％和65.4μg/g；在24h内，吸附过程是一不依赖温度的过程；实验中所用的金属离子对烟台红藻的铀吸附能力的影响程度在不同的时间段有所不同。     

预辐射聚丙烯膜接枝甲基丙烯酸聚乙二醇酯及其性能研究

采用预辐射接枝法对预辐射的聚丙烯（ＰＰ）膜接枝不同分子量的甲基丙烯酸聚乙二醇酯（ＰＥＧＭＡ）。分别研究了不同接枝溶液体系对接枝率的影响;通过全反射傅里叶红外光谱（ＦＴＩＲ－ＡＲＴ）和水接触角等的测定,观察了接枝前后ＰＰ膜表面性能的变化;还接枝前后ＰＰ膜绎血液蛋白吸附、血小弧的吸附以及样品表面血栓量等,以比较接枝前后样品的血液相容性。     

镧系裂变产物（La、Ce、Pr和Nd）在α-U表面偏析行为的第一原理研究 #br#

镧系裂变产物引起的燃料肿胀及包壳脆化是UZr金属燃料服役中的主要问题。其快速扩散通常借助于裂变气体释放通道,实验可观察到镧系裂变产物会在UZr金属燃料氙气泡处偏析。为理解裂变产物扩散机理及表面偏析现象,本文采用第一原理方法,对低温α-U中（100）、（112）、（001）、（021）、（110）、（010）表面的原子结构及形成能进行了研究,并讨论了常见镧系裂变产物La、Ce、Pr和Nd在不同表面的偏析行为。计算结果表明,（110）表面的形成能最低,为1.75 J/m²,（112）、（021）和（001）表面的形成能次之,为1.81~1.83 J/m²,（010）和（100）表面的形成能最高,分别为1.96 J/m²和2.04 J/m²。4种裂变产物在6种表面都表现出明显的偏析效应,对于同一种表面,其偏析驱动力排序为：La>Ce>Pr>Nd。对于同一种镧系裂变产物,偏析能随层间距的增加而减小。此外,采用Mc-Lean方程从热力学上评估了4种裂变产物在α-U表面的占据率,结果表明在服役温度范围内,4种镧系裂变产物均表现出明显的表面偏析。