Time-Dependence of Cold Neutron Pulse Emitted from Methane at 20°K

The time-dependent behavior of monochromatic neutrons from a pulsed cold moderator system provides important information for application of the system as a pulsed cold neutron source. The time distribution of neutron pulses from 20°K methane has been studied using time-of-flight and crystal monochromator techniques. The first time-moments of the neutron pulses and the thermalization time constant have been obtained.     

中国先进研究堆冷中子源单相冷包方案可行性分

在现有的冷源设计中,两相氢循环因其换热能力强而被广泛采用,但它最大的缺点是存在含气率影响慢化的稳定性。能否采用单相循环代替两相循环实现高热流密度的热量输出,是待研究的重点。为兼顾循环流量等宏观特性和流场、温度场分布等细节参数的分析,提出了一种基于迭代的耦合算法,将一维理论公式与三维数值仿真模型相结合,用于分析中国先进研究堆单相冷包方案的可行性。研究发现,单相循环只能带走约30%的核发热,但由于冷包增加了氦冷却套,其余热量全部通过氦气对冷包壁面的直接冷却带走。温度场的分析显示液氢和壁面的最高温度分别为21.7和23.7 K。这说明冷包得到了充分冷却,单相循环及单相冷包结构可满足工程需要。     

油田输水管道不停输清洗

针对输水管道的生产需要和管道内部结垢情况,结合所取管道内垢样溶垢试验,采用不停输化学清洗技术。清洗后,输水压力下降、流量显著提高。在清洗过程中,加入防塌减速剂和硫化氢抑制剂,在清洗除垢的同时,很好地解决了大量污垢脱落堵塞管道及产生硫化氢气体带来的安全问题。     

How do health and biological age influence chronological age and sex differences in cognitive aging: Moderating, mediating, or both?

Much research on cognitive competence in normal older adults has documented age and sex differences. The authors used new cross-sectional data from the Victoria Longitudinal Study (VLS) (n = 386; age 61 to 95 years) to examine how health and biological age influence age and sex differences in cognitive aging. The authors found evidence for both moderating and mediating influences. Age differences were moderated by health status, such that the negative effects of age were most pronounced among participants of relatively better health. Sex differences were moderated by health and were more pronounced among participants reporting comparatively poorer health. Although health mediated a notable amount of age-related cognitive variation, BioAge mediated considerably more variance, even after statistical control for differences in health. A complex pattern emerged for the mediation of sex differences: Although BioAge accounted for sex-related variation in cognitive performance, health operated to suppress these differences. Overall, both health and BioAge predicted cognitive variation independently of chronological age. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Do individual coping strategies help or harm in the work–family conflict situation? Examining coping as a moderator between work–family conflict and well-being.

In this study we examined the moderator role of coping (problem-, emotion-, and avoidance-focused coping strategies) between work-to-family and family-to-work conflict and well-being (work engagement, job satisfaction, and family satisfaction). The study was based on a sample of 527 Finnish workers. Hierarchical moderated regression analyses showed that emotion-focused coping buffered against job dissatisfaction in a high family-to-work conflict situation. On the other hand, emotion-focused coping was harmful for family satisfaction in the same stressful situation: Those who used more emotion-focused coping were less satisfied with their family life under the conditions of high family-to-work conflict. Furthermore, avoidance coping was beneficial in a high family-to-work conflict situation: Those who used more avoidance coping were more satisfied with their family life in this situation. No buffering effects were found for work engagement or for problem-focused coping. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Thermoluminescence measurements of neutron streaming through JET Torus Hall ducts

Thermoluminescence detectors (TLD) were used for dose measurements at JET. Several hundreds of LiF detectors of various types, standard LiF:Mg,Ti and highly sensitive LiF:Mg,Cu,P were produced. LiF detectors consisting of natural lithium are sensitive to slow neutrons, their response to neutrons being enhanced by ⁶Li-enriched lithium or suppressed by using lithium consisting entirely of ⁷Li. Pairs of ⁶LiF/⁷LiF detectors allow distinguishing between neutron/non-neutron components of a radiation field. For detection of neutrons of higher energy, polyethylene (PE-300) moderators were used. TLDs, located in the centre of cylindrical moderators, were installed at eleven positions in the JET hall and the hall labyrinth in July 2012, and exposure took place during the last two weeks of the experimental campaign. Measurements of the gamma dose were obtained for all positions over a range of about five orders of magnitude variation. As the TLDs were also calibrated in a thermal neutron field, the neutron fluence at the experimental position could be derived. The experimental results are compared with calculations using the MCNP code. The results confirm that the TLD technology can be usefully applied to measurements of neutron streaming through JET Torus Hall ducts.     

Investigation of thermal neutron scattering data for BeF2 and LiF crystals

The influences of thermal neutron scattering data for BeF₂ and LiF crystals on molten salt reactor physics are investigated in this work. Based on the structure parameters of BeF₂ and LiF, the coherent scattering for both crystals is added to NJOY source code. The ENDF6 format thermal neutron scattering sub-libraries for both crystals are evaluated with their phonon spectra using LEAPR; the ACE format data are produced by NJOY subsequently. Finally, the effect of thermal neutron scattering of BeF₂ and LiF crystals on k _eff and spectrum are investigated. The result shows that thermal neutron scattering for bound state of BeF₂ and LiF influence k _eff and spectrum obviously. The elastic scattering cross section for bound state of crystals is smaller than free atom; it makes k _eff decrease (1%–2%) and spectra be hardened. The higher temperature the bound state has, the smaller coherent elastic scattering cross section it gets; therefore, k _eff decreases with temperature. It is suggested that the thermal neutron data of LiF and BeF₂ should be taken into account for molten salt reactor.     

Neutronic Optimization of Premoderator and Reflector for Decoupled Hydrogen Moderator in 1 MW Spallation Neutron Source

For a decoupled liquid-hydrogen moderator, optimization studies have been performed on a premoderator and reflector materials (Pb, Be, Fe and Hg) together with several decoupling energies to realize a higher neutronic performance. The result indicated that, among four reflector materials mentioned above, the best neutronic performance could be obtained by adopting a Pb reflector with an optimized premoderator and an appropriate decoupling energy.     

慢化体中引入孔道改善煤中C、O测量的初探

对使用14MeV中子进行煤质分析检测的装置,论文提出了一种通过在慢化体中引入孔道来改善C和O元素测量的方法。为检验该方法,对无孔道、竖直孔道,斜孔道等不同的情形,进行了Monte-Carlo模拟计算和分析讨论。研究结果表明,使用该方法来改善C和O元素的测量是可行的,并且与源的位置和探测器的位置均相关的斜孔道具有较好的应用前景。     

Study on B4C decoupler with burn-up reduction aiming at 1-MW pulsed neutron source

In pulsed neutron sources, a neutron absorber called decoupler, which is characterized by a decoupling energy (Ed), is attached to the moderator to sharpen the neutron pulses for achieving good neutron energy resolutions. Cadmium and boron carbide (B₄C) are widely used as the decoupler materials. However, it is difficult to use B₄C in MW-class spallation neutron sources owing to high burn-up, which decreases Ed and increases helium gas swelling due to neutron absorption. To solve these issues concerning a B₄C decoupler, we introduce the concept of pre-decoupler to reduce neutron absorption in the B₄C decoupler, which is sandwiched by appropriate neutron absorption materials. Then, we study impacts of the pre-decouplers on B₄C decoupler in terms of burn-up by performing simplified model calculations. It is shown that neutron absorption in B₄C is reduced by 60% by using a Cd pre-decoupler without neutron intensity penalty. Moreover, helium gas swelling in B₄C is restrained to be one-third of the value when not using the pre-decoupler.