Anthropogenic I in the atmosphere: Overview over major sources, transport processes and deposition pattern

Wet and, to a lesser extent, dry deposition of atmospheric ¹²⁹I are known to represent the dominating processes responsible for ¹²⁹I in continental environmental samples that are remote from ¹²⁹I sources and not directly influenced by any liquid ¹²⁹I release of nuclear installations. Up to now, however, little is known about the major emitters and the related global deposition pattern of ¹²⁹I.In this work an overview over major sources of ¹²⁹I is given, and hitherto unknown time-dependent releases from these were estimated. Total gaseous ¹²⁹I releases from the US and former Soviet reprocessing facilities Hanford, Savannah River, Mayak, Seversk and Zheleznogorsk were found to have been 0.53, 0.27, 1.05, 0.23 and 0.14 TBq, respectively. These facilities were thus identified as major airborne ¹²⁹I emitters.The global deposition pattern due to the ¹²⁹I released, depending on geographic latitude and longitude, and on time was studied using a box model describing the global atmospheric transport and deposition of ¹²⁹I. The model predictions are compared to ¹²⁹I concentrations measured by means of Accelerator Mass Spectrometry (AMS) in water samples that were collected from various lakes in Asia, Africa, America and New Zealand, and to published values.As a result, both pattern and temporal evolution of ¹²⁹I deposition values measured in and calculated for different types of environmental samples are, in general, in good agreement. This supports our estimate on atmospheric ¹²⁹I releases and the considered substantial transport and deposition mechanisms in our model calculations.     

Design and construction of a multi-sensor position monitoring system applied to key components of synchrotron sources

Abstracts High-accuracy position monitoring of key components is required for modern synchrotron sources, such as free-electron lasers and diffraction-limited storage rings. Although various position monitoring sensors have been adopted to monitor the displacement of key compo-nents in each direction in real time, these monitoring sys-tems are usually based on their own coordinate system. Data from such systems are meaningful when evaluating and examining the data from each positioning monitoring system in a unified coordinate system. This paper presents the design and construction of a multi-sensor position monitoring system (MPMS). A hydrostatic levelling sys-tem, a wire position sensor (WPS) and a tiltmeter are fixed to a stainless steel plate that has been calibrated by a coordinate-measurement machine. Several plates form the MPMS. The system must compensate for the sag of the stretched wires so that the WPSs create a straight line. The method of the coordinate transformation from the sensor coordinate system to the MPMS coordinate system was thoroughly studied. An experimental MPMS that includes five plates was setup in a 20-m tunnel, and a validation study to verify fully the feasibility of the MPMS was performed.     

加速器磁铁电源的被控对象辨识模块设计

国内加速器磁铁电源的控制策略基本上以比例-积分-微分(Proportion-Integral-Derivative,PID)控制为主,对被控对象的处理是基于物理模型归纳传递函数,并在此基础上设计控制器。该方法受制于物理模型中元器件参数的不精确性和结构上的不确定性,更重要的是控制器设计一般不关注被控对象的内部机理而是其输入输出(Input-output,I/O)特性。本文提出一种可工作于电源数控平台上的辨识建模方法,其表现出了更好的实时性、适用性和通用性。借助一类子空间模型辨识方法(Multivariable Output Error State s Pace,MOESP),在现场可编程逻辑门阵列(Field Programmable Gate Array,FPGA)上有针对性地设计模块,并使用可编程片上系统(System On a Programmable Chip,SOPC)集成软核处理器来完成数据处理和参数计算。基于北京正负电子对撞机II期(Beijing Electron Positron Collider II,BEPCII)和加速器驱动次临界系统(Accelerator Driven Sub-critical System,ADS)磁铁电源数控平台的被控对象辨识模块已成功运用在BEPCII和ADS电源样机上。经过严格的测试表明,辨识模型可以对电源的实际输出电流作出较精确的预报。该辨识模块易于使用,为控制系统设计提供了关键信息,适用于各种特性的负载。     

Measurement of the natural ^36Cl and ^236U in uranium mineral with accelerator mass spectrometry

The concentration of the natural ultra-trace radionuclides CI and U in the uranium depended on the neutron flux.In this article,a method for measuring ³⁶C1 and ²³⁶U in the same uranium mineral with accelerator mass spectrometry was developed in China Institute of Atomic Energy,providing a protocol of the potential application of ²³⁶U in uranium mining,environmental,and geological research.The two samples were from Guangxi and Shanxi province,China,and their ratios ³⁶Cl/C1 and ²³⁶U/²³⁸U were measured.More experimental data conduced to understand the natural nuclides in the uranium mineral.We plan to conduct more efforts on the research.     

Corrosion resistance of ceramics SiC and Si3N4 in flowing lead-bismuth eutectic

A corrosion test was conducted to investigate the corrosion characteristics of SiC and Si₃N₄ in a flowing lead-bismuth eutectic (Pb-Bi) with a fluid temperature of 550 °C, a velocity of 1 m/s, and an oxygen concentration of 1 × 10⁻⁶ wt% for an exposure time of 2000 h. The weight losses of the SiC and Si₃N₄ specimens were lower than those of corrosion-resistant steels tested under the same condition. The specimens showed excellent resistance against an element dissolution and an oxidation in the Pb-Bi flow. The surface was slightly damaged due to some stresses of the Pb-Bi flow and/or those generated by adhered Pb-Bi in the test procedure.     

Enhancing TRU burning and Am transmutation in Advanced Recycling Reactor

This paper presents about conceptual designs of Advanced Recycling Reactor (ARR) focusing on enhancement in transuranics (TRU) burning and americium (Am) transmutation. The design has been conducted in the context of the Global Nuclear Energy Partnership (GNEP) seeking to close nuclear fuel cycle in ways that reduce proliferation risks, reduce the nuclear waste in the US and further improve global energy security. This study strives to enhance the TRU burning and the Am transmutation, assuming the development of related technologies in this study, while the ARR based on mature technologies was designed in the previous study. It has followed that the provided TRU burning core is designed to burn TRU at 28 kg/TW_thh, by adding moderator pins of B₄C (Enriched B-11) and the Am transmutation core will be able to transmute Am at 34 kg/TW_thh, by locating Am blanket of AmN around the TRU burning core. It indicates that these concepts improve TRU burning by 40-50% than the previous core and can transmute Am effectively, keeping the void reactivity acceptable.     

Accelerator mass spectrometry of U at low energies

The performance of the compact ETH-TANDY system for accelerator mass spectrometry measurements of ²³⁶U is presented. Despite the low ion energies of around 1.2 MeV we can demonstrate a background level that is comparable to larger facilities. The careful ion-optical design of the high-energy spectrometer leads to a high suppression of neighboring isotopes sufficient to measure samples with isotopic ratios of ²³⁶U/²³⁸U > 10^-11 the ion chamber only, as demonstrated by systematic investigations with different slit settings and time-of-flight measurements. Additionally, a high overall efficiency is achieved due to a high transmission through the accelerator.     

Forensic applications of C at CIRCE

The decreasing trend of the radiocarbon pulse produced during the atmospheric tests of nuclear weapons (bomb-carbon) coupled with high sensitivity accelerator mass spectrometry (AMS) measurements, drastically increased the precision of radiocarbon age determinations since the second part of the sixties, allowing the application of radiocarbon AMS to a wide range of studies previously not directly involving conventional radiocarbon dating (i.e. food authenticity, forensic, biochemistry). In the framework of authenticity evaluation of artworks, high precision radiocarbon (¹⁴C) AMS measurements (ΔR/R < 0.3%) reduce the conventional uncertainty of the dating to few decades, allowing precise age estimation of materials containing carbon (C). The Centre for Isotopic Research on Cultural and Environmental heritage (CIRCE) during its activity on AMS ¹⁴C dating achieved high precision measurements opening the opportunity to these kinds of applications. This paper presents the main results obtained from radiocarbon measurements on a set of bone samples analyzed for the determination of the post-mortem interval in the framework of an unsolved case investigated by the Rome prosecutor office. The chronological characterization of the wooden support of the “Acerenza portrait” is also presented with the aim to evaluate its age and to further investigate the possibility to attribute this artwork to Leonardo da Vinci.Bomb-¹⁴C dating on the lipid and collagen fractions of bones allows the evaluation of the year of the death of the individuals by means of ad hoc calibration data sheet with the typical few years precision and difference between collagen apparent age and the year of death appeared in agreement with the age of one individual estimated by dating of tooth collagen. Conventional radiocarbon dating on both wood and wood extracted cellulose leads to an estimation of the portrait wood board age (2σ) of 1459-1524 AD (57% relative probability), 1571-1631 AD interval (42% relative probability).and 1559-1563 AD (1% relative probability). These results attribute with the highest relative probability an age comprised within the life span of Leonardo (1452-1519) to the support.     

DNA double-strand breaks induced along the trajectory of particles

It is well-known that the DNA damage caused by charged particles considerably differs from damage due to electromagnetic radiation. In the case of irradiation by charged particles the DNA lesions are more complex and clustered. Such clustered damage is presumed difficult to be repaired, and is potentially lethal. In this study, we utilize a 90°-scattering system and related imaging techniques to investigate the accumulation of γ-H2AX along the trajectory of charged particles. By immunostaining the γ-H2AX protein, optical images of corresponding double strand breaks were observed using a high resolution confocal microscope. We demonstrate the difference in the accumulation of γ-H2AX from irradiation by 1 MeV protons and that of 150 keV X-rays. The acquired images were arranged and reconstructed into a 3D image using ImageJ software. We discovered that the γ-H2AX foci, following irradiation by protons, have a tendency to extend in the beam direction, while those from X-ray irradiation tend to be smaller and more randomly distributed. These results can be explained by the physical model of energy deposition.     

A study on low magnetic permeability gas tungsten arc weldment of AISI 316LN stainless steel for application in electron accelerator

Low magnetic permeability is an important criterion in selection of the material of construction of beam pipes and vacuum chambers of electron accelerators for safeguarding against distortion of the magnetic field. In the modified design of new 20 MeV/30 mA Injector Microtron for the existing synchrotron radiation sources Indus-1 and Indus-2, AISI 316 LN stainless steel has been identified as the material of construction of its vacuum chamber. Welding of AISI 316LN stainless steel with conventional filler alloys like ER316L and ER317L of AWS A5.9 produces duplex weld metal with 3–8% ferro-magnetic delta ferrite to avoid solidification cracking. The results of the study has demonstrated that GTAW of AISI 316LN SS with high Mn adaptation of W 18 16 5 N L filler produced a crack free non-magnetic weld with acceptable mechanical properties. Moreover, AISI 316LN stainless steel is not required to be solution annealed after the final forming operation for obtaining a low magnetic permeability, thereby avoiding solution annealing of large vacuum chamber in vacuum/controlled atmosphere furnace and associated problems of distortion. Besides Injector Microtron, the study also provides useful input for design of future indigenous accelerators with vacuum chambers of austenitic stainless steel.