Measurement of the ground state 2n pickup probability for 28Si+68Zn and its role in sub-barrier fusion enhancement

The ground state and excited state transfer yields for the 2-neutron pickup channel in the ²⁸Si+⁶⁸Zn system have been measured explicitly. The recoil mass separator at the nuclear Science Centre, New Delhi was used for the measurement. A NaI(T1) detector was used for detecting the deexcitation γ’s from the transfer products. The kinematic coincidence technique was employed for the transfer measurement. Simplified coupled channels calculations show that out of all transfer channels the major contribution to the sub-barrier enhancement comes from the ground state 2 neutron pickup channel with a ground state Q-value of+1.83 MeV.     

近垒重离子熔合反应中的中子转移效应(英文)

近势垒及其以下能区重离子熔合反应中的中子转移耦合道效应是一个复杂且有争议的问题。简要介绍了近年来在中国原子能科学研究院的HI-13串列加速器上,基于静电偏转板装置完成的32S+90,94,96Zr,18O+74Ge和18O+58Ni等几个典型体系的熔合反应研究情况,并结合耦合道理论对实验数据进行了分析。选取反应体系时同时关注了正Q值的中子拾取和削裂道。另外,基于完全耦合道理论计算,提出了一种能够定量提取熔合反应中中子转移效应的自洽方法。这些研究进一步证实了垒下重离子熔合反应中的中子转移效应,同时指出了其复杂性。需要进一步的实验和理论研究来澄清相关核反应机制。The effect of neutron transfers on near-and sub-Coulomb-barrier fusion of heavy-ions is still a complicated and controversial problem. This paper reviews the recent experimental results of the fusion excitation functions of several typical systems, which have been measured by using an electrostatic deflector setup at the HI-13 tandem accelerator of CIAE. Both the neutron pickup and stripping effects were studied. Moreover, a self-consistent method to reliably isolate the transfer effect quantitatively based on the coupledchannels calculation is proposed. These studies give a further support for the neutron transfer effect on sub-barrier fusion of heavy-ions and its complexity. Further experimental and theoretical studies are needed for clarifying the relevant reaction mechanisms.     

Survey of deep sub-barrier heavy-ion fusion hindrance phenomenon forpositive and negative Q-value systems using the proximity-type potential

A systematic survey of the accurate measurements of heavy-ion fusion cross sections at extreme sub-barrier energies is performed using the coupled-channels (CC) theory that is based on the proximity formalism. This work theoretically explores the role of the surface energy coefficient and energy-dependent nucleus-nucleus proximity potential in the mechanism of the fusion hindrance of 14 typical colliding systems with negative \begin{document}$Q$\end{document}-values, including ¹¹B+¹⁹⁷Au, ¹²C+¹⁹⁸Pt, ¹⁶O+²⁰⁸Pb, ²⁸Si+⁹⁴Mo, ⁴⁸Ca+⁹⁶Zr, ²⁸Si+⁶⁴Ni, ⁵⁸Ni+⁵⁸Ni, ⁶⁰Ni+⁸⁹Y, ¹²C+²⁰⁴Pb, ³⁶S+⁶⁴Ni, ³⁶S+⁹⁰Zr, ⁴⁰Ca+⁹⁰Zr, ⁴⁰Ca+⁴⁰Ca, and ⁴⁸Ca+⁴⁸Ca, as well as five typical colliding systems with positive \begin{document}$Q$\end{document}-values, including ¹²C+³⁰Si, ²⁴Mg+³⁰Si, ²⁸Si+³⁰Si, ³⁶S+⁴⁸Ca, and ⁴⁰Ca+⁴⁸Ca. It is shown that the outcomes based on the proximity potential along with the above-mentioned physical effects achieve reasonable agreement with the experimentally observed data of the fusion cross sections \begin{document}$\sigma_{\rm{fus}}(E)$\end{document}, astrophysical \begin{document}$S(E)$\end{document} factors, and logarithmic derivatives \begin{document}$L(E)$\end{document} in the energy region far below the Coulomb barrier. A discussion is also presented on the performance of the present theoretical approach in reproducing the experimental fusion barrier distributions for different colliding systems.     

Static versus energy-dependent nucleus–nucleus potential for description of sub-barrier fusion dynamics of _8~(16)O+_(50)~(112,116,120)Sn reactions

The static and energy-dependent nucleus–nucleus potentials are simultaneously used along with the Wong formula for exploration of fusion dynamics of168O+112,116,12050 Sn reactions. The role of internal structure degrees of freedom of colliding pairs, such as inelastic surface vibrations, are examined within the context of coupled channel calculations performed using the code CCFULL. Theoretical calculations based on the static Woods–Saxon potential along with the one-dimensional Wong formula fail to address the fusion data of168O+112,116,12050 Sn reactions.Such discrepancies can be removed if one uses couplings to internal structure degrees of freedom of colliding nuclei.However, the energy-dependent Woods–Saxon potential model(EDWSP model) accurately describes the sub-barrier fusion enhancement of168O+112,116,12050 Sn reactions. Therefore, in sub-barrier fusion dynamics, energy dependence in the nucleus–nucleus potential governs barrier modification effects in a closely similar way to that of the coupled channel approach.     

Transfer reactions and sub-barrier fusion in 40Ca + 90, 96Zr

The two systems ⁴⁰Ca + ^90,96Zr have been studied by measuring nucleon transfer reactions at two energies near the Coulomb barrier, thus complementing the available sub-barrier fusion cross-sections. Angular distributions for various transfer channels have been determined. Significantly larger neutron transfer cross-sections are found for the target ⁹⁶Zr that exhibits the larger enhancement in the sub-barrier fusion cross-sections. All data have been analyzed with a new model for heavy-ion collisions that calculates simultaneously transfer cross-sections, fusion excitation functions and barrier distributions. The model gives a good account of both transfer and fusion data. Received: 2 May 2002 / Accepted: 4 June 2002 / Published online: 26 November 2002 RID="a" ID="a"e-mail: montagnoli@pd.infn.it, Fax +39049 8277102, Tel. +39049 8277117. RID="b" ID="b"On leave from the China Institute for Atomic Energy, 102413 Beijing, China. Communicated by C. Signorini     

氘氚聚变中子发生器旋转氚靶传热特性研究

强流氘氚中子发生器可用于模拟聚变堆中子环境, 对于开展聚变堆包层材料相关实验研究具有重要意义. 本文提出了一种用于10¹² n·^-1量级氘氚中子发生器HINEG (high intensity neutron generator)的旋转氚靶系统设计方案, 并对其技术难点和强化传热方法进行了介绍. 为考查该氚靶系统的传热特性, 利用Computational Fluid Dynamics方法对冷却水层厚度、冷却水流速和氚靶系统旋转速度对靶面冷却的影响进行了分析, 并对不同热功率密度下靶面的传热过程进行了研究. 结果显示, 大的水层厚度、大的冷却水流速和高的靶系统旋转速度有利于靶面的冷却, 但水层厚度和水流速的变化对靶面传热影响较小. 一定条件下靶面所承受的热功率密度不能超过某个限值.     

先进燃料聚变反应性增强的新机制

采用电子回旋波加热D-^３Ｈe先进燃料聚变等离子体，使它处在高的电子温度下，一些新的物理过程(如聚变产物之间核-核弹性散射、核力与库仑相干散射及核反应的传播)变得相对重要，而高能聚变产物离子与电子的库仑相互作用相对变弱.部分本底燃料离子被高能的聚变反应产物核击出而提升到分布函数尾部成为“超热”燃料离子，从而可能提高D-^３Ｈe聚变的反应性.还计算了这些机制的能量传递. 关键词： 核-核弹性散射 核-库仑相干散射 ３Ｈe聚变')" href="#">D-^３Ｈe聚变 聚变反应性增强     

分子激发中的表面等离激元增强效应

金属纳米粒子的表面等离激元增强效应是纳米科学领域的一个研究热点.针对染料分子与金属纳米粒子的耦合系统,应用偶极-偶极近似计算分子与金属纳米粒子的库仑相互作用,并应用密度矩阵理论描述在不同极化方向的电场作用下的电荷输运过程,分析了分子与金属纳米粒子在不同相对位置下分子激发态的动力学过程,发现表面等离激元的增强效应与分子和金属钠米粒子的相对位置以及等离激元的耗散系数有密切关系,详细讨论了分子与金属纳米粒子间的耦合强度、外场的极化方向、等离激元的寿命及共振激发条件对分子激发态及表面等离激元增强的影响,分析了分子-金属纳米粒子耦合系统中表面等离激元增强效应的物理本质.     

Near-barrier fusion of Sn + Ni and Te + Ni systems: examining the correlation between nucleon transfer and fusion enhancement

The fusion excitation functions for radioactive (132)Sn + (58)Ni and stable (130)Te + (58,64)Ni were measured at energies near the Coulomb barrier. The coupling of transfer channels in heavy-ion fusion was examined through a comparison of Sn + Ni and Te + Ni systems, which have large variations in the number of positive Q-value nucleon transfer channels. In contrast with previous experimental comparisons, where increased sub-barrier fusion cross sections were observed in systems with positive Q-value neutron transfer channels, the reduced excitation functions were equivalent for the different Sn + Ni and Te + Ni systems. The present results suggest a dramatically different influence of positive Q-value transfer channels on the fusion process for the Sn + Ni and Te + Ni systems.     

Bayesian analysis on non-resonant behavior of 12C + 12C fusion reaction at sub-barrier energies

Controversies exist among experiments and theories on the begin{document}$ S^star$end{document} factor of the astrophysical important reaction ¹²C + ¹²C for energies below 3 MeV. Only frequentist approaches have been used so far for data analysis, and the confidence levels or theoretical errors are not available from previous theoretical predictions. In this study, the Bayesian method is employed to provide theoretical predictions and its 1σ confidence level based on all the currently available experimental data for the first time. The improved coupled-channels model CCFULL-FEM implemented with the finite element method as well as the Markov chain Monte Carlo approach emcee are adopted to analyze the non-resonant behavior of this reaction. The posterior distribution of the Woods-Saxon potential parameters is investigated. Compared with the widely used frequentist method MIGRAD within the Minuit minimization program, the Bayesian method has a significant advantage for exploring the potential parameter space. When the existing experimental data measured down to subbarrier energies are considered, the potential parameters are constrained to a very narrow range, and the predictions of the begin{document}$ S^star$end{document} factor showed no sharp decrease in the low-energy region.     

HL-2A装置上DD热核聚变中子产额和通量的估算

用蒙特卡罗方法,利用MCNP3B编码计算了HL 2A装置芯部离子温度为5keV、离子密度为5×1013cm-3的DD热核聚变中子产额的空间分布,以及高场边A、低场边D、偏滤器的B和C点所在位置各种能量的中子辐射通量和平均通量。计算了由于D+D→P+T反应产生氚,在10%的氚与氘发生DT反应产生中子的条件下,热核聚变中子的产额以及在A、B、C、D各位置通量发生的变化。计算结果为发展新的聚变中子诊断系统、辐射防护和环境评估提供了依据。     

HT-7上氘等离子体放电时中子注量的测量与分析

利用三氟化硼（BF₃） 和氦三（3He）正比计数管组成的快速时间分辨中子注量探测系统,对HT-7超导托卡马克上氘等离子体放电时光中子和聚变中子的产生机理进行研究.结合γ射线、硬X射线等相关诊断的实验结果,分析了纯欧姆放电和低杂波辅助加热放电时,中子注量信号随时间演化的典型特征.结果表明：HT-7在投入大功率低杂波辅助加热等离子体放电时,能够产生数量可观的氘-氘（D-D）聚变中子. 关键词： 中子注量 聚变中子 光中子 托卡马克     

Self-consistent treatment of spin and magnetization dynamic effect in spin transfer switching

The effect of itinerant spin moment (m) dynamic in spin transfer switching has been ignored in most previous theoretical studies of the magnetization (M) dynamics. Thus in this paper, we proposed a more refined micromagnetic model of spin transfer switching that takes into account in a self-consistent manner of the coupled m and M dynamics. The numerical results obtained from this model further shed insight on the switching profiles of m and M, both of which show particular sensitivity to parameters such as the anisotropy field, the spin torque field, and the initial deviation between m and M.     

Measurement of dose enhancement by neutron capture of boron in Cf interstitial brachytherapy

The effect of boron concentration in water on the gamma, fast and slow neutrons and alpha particles components at the central, forward and backward surfaces inside tumor phantom of 4.2 cm diameter and 4.4cm height, during brachytherapy by neutrons from ²⁵²Cf were investigated. The source was at the centre of a cubic shaped water phantom of 30 cm side. The study was carried for different concentrations of boron from H₃BO₃, Li₂B₄O₇ and H₃¹⁰BO₃. The effect of source to tumor distance on the different components of radiation was also measured. The results indicated that the use of ¹⁰B compounds enhances the damage and is recommended for successful boron neutron capture therapy (BNCT).     

纳米流体应用于强化传热的研究进展及面临的挑战

纳米流体是近年来新兴的一种强化传热工质,其在强化传热领域有着广阔的应用前景,然而目前对纳米流体强化传热应用的研究还存在一些障碍。本文从纳米流体的制备和传热特性方面总结了近几年的研究进展,并提出了研究过程中需要克服的几个问题,以促进今后进一步的研究工作。     

Intriguingly high convective heat transfer enhancement of nanofluid coolants in laminar flows

We reported on investigation of the convective heat transfer enhancement of nanofluids as coolants in laminar flows inside a circular copper tube with constant wall temperature. Nanofluids containing Al₂O₃, ZnO, TiO₂, and MgO nanoparticles were prepared with a mixture of 55 vol.% distilled water and 45 vol.% ethylene glycol as base fluid. It was found that the heat transfer behaviors of the nanofluids were highly depended on the volume fraction, average size, species of the suspended nanoparticles and the flow conditions. MgO, Al₂O₃, and ZnO nanofluids exhibited superior enhancements of heat transfer coefficient, with the highest enhancement up to 252% at a Reynolds number of 1000 for MgO nanofluid. Our results demonstrated that these oxide nanofluids might be promising alternatives for conventional coolants.     

Heat transfer enhancement by combination of serpentine curves and nanofluid flow in microtube

Heat transfer and flow characteristics of Cu/water nanofluids' flow in the serpentine microtubes are investigated experimentally. The serpentine microtubes are fabricated by bending a straight copper microtube with an inner diameter of 787 μm. Also, the Cu/water nanofluids are prepared using a novel one-step technique, namely electro-exploded wire. The effects of serpentine microtubes' geometrical parameters (pitch spacing, p, and straight section, l) and nanofluid concentration (weight fraction, φ) are examined. It is found that the heat transfer enhances by decreasing both the pitch spacing and the straight section of the serpentine microtube as well as increasing the weight fraction of the nanofluid. Also, the results show that the friction factor tends to increase in the same manner. A noticeable average enhancement in the thermal performance factor of 21.8% is obtained for a specific operating condition, i.e., the nanofluid at φ = 0.3% through the serpentine microtube with p = 9.6 mm and l = 10 mm. Finally, two correlations of Nusselt number and friction factor for the Cu/water nanofluids across the serpentine microtubes are proposed.     

40,48Ca+90,96Zr融合反应的动力学模型研究

应用改进的量子分子动力学模型,在严格挑选初始核考虑弹靶结构效应的基础上,研究了近垒和垒上融合反应^40,48Ca+^90,96Zr. 研究表明: 4个反应的理论计算截面与实验值很好符合; 丰中子反应⁴⁰Ca+⁹⁶Zr的垒下融合截面比其他3个反应有明显增强的现象.为了理解丰中子反应⁴⁰Ca+⁹⁶Zr与⁴⁰Ca+⁹⁰Zr相比垒下融合截面增强,而Ca+⁹⁶Zr垒下融合截面没有明显增强的原因, 进一步分析了484个反应的融合位垒,中子转移与融合位垒的关系、中子转移与Q值的关系,结果表明: 正反应Q值会引起核子(特别是中子)转移的增强,从而导致动力学融合位垒的下降和垒下融合截面增强.     

Fluorescence enhancement of samarium complex co-doped with terbium complex in a poly(methyl methacrylate) matrix

The fluorescence property of Sm(DBM)₃phen- (DBM—dibenzoylmethide, phen—1,10-phenanthroline) and Tb(DBM)₃phen-co-doped poly(methyl methacrylate) (PMMA) was investigated. The excitation, emission spectra and fluorescence lifetime of the co-doped samples were examined. In the co-doped samples, the luminescence intensities of Sm³⁺ enhance with an increase of the Tb(DBM)₃phen content and with a decrease of the Sm(DBM)₃phen content. The reason for the fluorescence enhancement effect in the co-doped polymer is the intermolecular energy transfer. To give a vivid picture for this co-doped system, a model for the fluorescence enhancement of Sm(DBM)₃phen- and Tb(DBM)₃phen-co-doped PMMA is presented.     

氨水降膜吸收传热传质强化的研究进展

综述了近年来应用于氨水降膜吸收性能强化的研究成果,总结了氨水降膜吸收的强化方法,分析了氨水降膜吸收过程中的影响因素,指出研究中的一些不足,并对该领域未来的研究方向进行了讨论,指出采用物理处理、化学处理和纳米技术三种强化手段相结合的方法是未来强化吸收可能的发展趋势。