17 熔合反应中动力学势垒的研究

用改进的量子分子动力学模型研究了与入射能量相关的重离子熔合反应的动力学势垒。在库仑势垒附近，随着入射能的降低可以观察到动力学势垒的最低值，这个最低动力学势垒与绝热势垒非常接近；另一方面，动力学势垒随着入射能的增加而升高，最终接近于静态势垒（非绝热势垒）。本工作研究发现，颈部的形成和体系的动力学形变是促使动力学势垒降低的主要原因。基于动力学势垒的研究，对于重离子熔合反应的额外推动（extra—push）给出了微观理解，并对熔合反应的势垒贯穿给出了一种全新的解释。     

熔合反应中动力学势垒的研究

用改进的量子分子动力学模型研究了与入射能量相关的重离子熔合反应的动力学势垒。在库仑势垒附近,随着入射能的降低可以观察到动力学势垒的最低值,这个最低动力学势垒与绝热势垒非常接近;另一方面,动力学势垒随着入射能的增加而升高,最终接近于静态势垒(非绝热势垒)。本工作研     

10 能量相关的动力学熔合势垒

用改进的量子分子动力学模型研究了与入射能量相关的重离子动力学熔合势垒。在库仑势垒附近，随着入射能的降低可以观察到动力学势垒的最低值，这个最低动力学势垒与绝热势垒非常接近；另一方面，动力学势垒随着入射能的增加而升高，当入射能增加到一定程度，动力学势垒变化很慢，越来越接近于静态势垒（非绝热势垒）。基于动力学势垒的研究，对于重离子熔合反应的额外推动extra-push给出了一个微观理解。     

从16O＋208Pb反应体系抽取核势的表面弥散参数

核势是核反应计算中的一个主要问题,常被参数化为Wood—Saxon形式。通常,取表面弥散参数为0．63fm能够再现弹性和非弹性散射的实验数据。然而,近来发现,表面弥散参数只有增大到0．75到1．5fm时,才能够再现高精度的近库仑势垒能区的熔合激发函数。目前,造成这种差异的原因尚不清楚。     

用背角准弹散射研究近库仑势垒能区重离子核反应

利用背角准弹散射的方法开展了近库仑势垒（近垒）能区重离子核反应机制的研究。高精度测量了深垒下能区16O+152,154Sm、184W、¹⁹⁶Pt和²⁰⁸Pb等体系的背角准弹散射激发函数,用耦合道计算抽取了核势的表面弥散参数,结果表明考虑耦合道效应得到的表面弥散参数值正常。基于背角准弹散射势垒分布对核结构的敏感性,尝试用深垒下能区16O+152Sm、170Er和174Yb等体系的背角准弹散射来抽取形变靶核的十六极形变参数,所抽取值与已有结果趋势一致,说明了该方法的可行性。此外,研究了弱束缚核体系的破裂效应,其表现为背角准弹势垒分布较全熔合势垒分布向低能移动,所得结果进一步说明势垒分布同时含有核结构和核反应机制的信息。     

p+~(107,109)Ag核反应数据的计算和分析

本工作通过理论计算的方法获得了一套适合入射能量为从阈值到200 MeV的p+107,109 Ag核反应全套微观数据。首先,使用光学模型理论进行调参计算,得到了一套适合入射能量为从阈值到340MeV的p+107,109 Ag核反应Becchetti-Greenlees光学势参数,这套参数与实验数据符合很好。其次,在这套光学势参数的基础上用扭曲波玻恩近似对入射能量从阈值到200MeV的p+107,109 Ag直接非弹性散射截面进行了计算。最后,使用核反应统计理论计算了入射能量从阈值到200MeV的p+107,109 Ag核反应各反应道的截面和出射粒子能谱,得到了该能区p+107,109 Ag核反应全套微观数据。将所有计算值与实验数据进行比较,结果表明,所得到的全套微观数据与实验数据符合很好。     

用背角准弹散射研究近库仑势垒能区重离子核反应

利用背角准弹散射的方法开展了近库仑势垒(近垒)能区重离子核反应机制的研究。高精度测量了深垒下能区~(16)O+~(152,154)Sm、~(184)W、~(196)Pt和~(208)Pb等体系的背角准弹散射激发函数,用耦合道计算抽取了核势的表面弥散参数,结果表明考虑耦合道效应得到的表面弥散参数值正常。基于背角准弹散射势垒分布对核结构的敏感性,尝试用深垒下能区~(16)O+~(152)Sm、~(170)Er和~(174)Yb等体系的背角准弹散射来抽取形变靶核的十六极形变参数,所抽取值与已有结果趋势一致,说明了该方法的可行性。此外,研究了弱束缚核体系的破裂效应,其表现为背角准弹势垒分布较全熔合势垒分布向低能移动,所得结果进一步说明势垒分布同时含有核结构和核反应机制的信息。     

非定域光学势研究裂变原子核

<正>光学模型是研究原子核反应的基本理论模型之一。入射粒子与靶核发生散射和反应,它们之间的光学势可以看作复杂的多体问题,理论上应该是非定域的。本工作基于Perey-Buck形式的非定域光学势研究非定域势对裂变核反应的影响。核子与核散射相应的Schrodinger方程为:     

~6Li+~(208)Pb光学势灵敏半径的能量相依性

光学势灵敏区域的确定是研究光学势性质的先决要素。本工作利用扰动法,抽取并研究了弱束缚体系~6Li+~(208)Pb光学势灵敏区域的能量相依性。结果表明,该体系光学势实部和虚部的灵敏区域均呈现多峰结构。内部的灵敏区域对应体系库仑势垒的穿透过程,其位置基本不随能量的变化而改变;而外部的灵敏区域则对应体系的表面相互作用过程,并且存在强烈的能量相依性。采用新的灵敏区域重新检测了~6Li+~(208)Pb光学势的性质,结果表明在新的灵敏区域内,~6Li+~(208)Pb光学势虚部表现出传统的阈异常现象,而并非之前所观察到的破裂阈异常现象。     

弱束缚原子核反应函数的系统学研究

破裂反应在弱束缚原子核的散射中是一个重要的反应道,尤其是在亚垒能区,实验上已尽力去研究破裂对亚垒熔合的影响。为了探索弱束缚原子核在不同靶核上的破裂道对于熔合截面的耦合效应的强弱,我们系统地分析了弱束缚原子核的弹性散射实验数据,并得到反应总截面。利用圣保罗势得到势垒参数,这样就可以得到弱束缚原子核在轻靶、中重靶和重靶上的反应函数F(x),然后与没有耦合道效应的普适函数F0(x)进行了比较。从两者的对比上,可以得到弱束缚原子核在轻靶上的破裂贡献小,在能量高于库仑位垒能区在中重靶和重靶上的破裂被压低,在亚垒能区有些弱束缚原子核在中重靶和重靶上的破裂增强,因此弱束缚原子核在中重靶和重靶上的研究还需要更多的实验。     

Extraction of Barrier Height from Experimental Fusion Excitation Function

The Coulomb barrier plays a critical role in the low energy heavy-ion reaction. However, it can not be directly measured and needs to be extracted by different types of nuclear reactions. There have been many systematic studies on the Coulomb barrier so far, but most of them rely heavily on the interaction potential model and the reaction theory. In this work, the first-order derivative of the product of experimental fusion cross section and energy with respect to the energy was used as the penetration coefficient, and the position at which the penetration coefficient equals to half of its maximum was defined as the empirical barrier height. This definition does not depend on the theoretical model and has excellent stability and reliability. Based on this definition, the coupled-channels model CCFULL and Wong formula were used to fit 12 representative series of experimental fusion functions, and their Coulomb barrier heights were extracted. By comparing the heights extracted from the experimental values and the heights predicted by different theoretical potential models, and also their variation with the isospin asymmetry, it is found that the Bass80 and WKJ formulas are most consistent with the results of this work.     

核形变在近垒和垒下能区阈反常和熔合反应中的效应

基于经典的一维势垒穿透模型 ,考虑核静态形变和动力学形变效应 ,建立了联系周边反应和熔合反应的模型———形变 能量相依的多维势垒穿透模型。该模型成功解释了19F 2 0 8Pb体系的一些实验现象 ,并指出动力学极化效应仅在库仑位垒附近起作用 ,而静态形变效应则在垒下能区起主要作用。这一结论说明 :在用冷熔合形成超重核时 ,使用形变的弹靶体系将有利于增强合成的截面     

Fusion Energy Without Strong Nuclear Radiation

Conventional quantum mechanics calculation shows that fusion energy without strong nuclear radiation is feasible, because this is the nature of sub-barrier nuclear fusion. When the Coulomb barrier is relatively thin and low, the resonant tunneling would select the fusion reaction with strong neutron and Gamma radiation. On the other hand, if the Coulomb barrier is thick and high, the resonant tunneling would select the fusion reaction without strong neutron and Gamma radiation. Thus, fusion energy with lowest radiation is predictable in terms of d + t fusion data. This is the harmony between various approaches towards fusion energy. What we lose is the assumption of compound nucleus model for light nuclei fusion, and what we gain is the fusion energy without strong neutron and Gamma radiation.     

Studies on p+6Li Fusion Reaction using 3-Parameter Model

The 3-parameter model introduces 3 parameters (radius of a square nuclear potential well, the real part and the imaginary part of the nuclear potential depth) to describe the low energy behavior of the fusion cross-section for light nuclei. It has been justified by the experimental data from the National Nuclear Data Center (NNDC) for 3 major fusion reactions (d?+?T, d?+?D, and d?+?³He). In the present paper this 3-parameter model has been extended to p+⁶Li fusion reaction. It agrees with the fusion cross-section data from NNDC again. Moreover it is able to calculate the astrophysical S-factor with an electron screening potential for p+⁶Li fusion reaction as well. As a development of the 3-parameter model, the necessary condition for a low energy resonant tunneling through Coulomb barrier is derived. It reveals further the possibility of resonant tunneling at very low energy for p+⁶Li system.     

Astrophysical S factors for fusion reactions involving C, O, Ne, and Mg isotopes

Using the São Paulo potential and the barrier penetration formalism we have calculated the astrophysical factor S(E) for 946 fusion reactions involving stable and neutron-rich isotopes of C, O, Ne, and Mg for center-of-mass energies E varying from 2 to ≈18-30 MeV (covering the range below and above the Coulomb barrier). We have parameterized the energy dependence, S(E), by an accurate universal 9-parameter analytic expression and present tables of fit parameters for all the reactions. We also discuss the reduced 3-parameter version of our fit which is highly accurate at energies below the Coulomb barrier, and outline the procedure for calculating the reaction rates. The results can be easily converted to thermonuclear or pycnonuclear reaction rates to simulate various nuclear burning phenomena, in particular, stellar burning at high temperatures and nucleosynthesis in high density environments.     

Studying the Effects of Compound Nucleus Energy on Coefficient of Surface Tension in Fusion Reactions Using Proximity Potential Formalism

In this investigation, the energy effects of compound nucleus are studied using formalism of proximity potential on the surface tension coefficient (γ). For this purpose, this coefficient in both main and final versions of proximity formalism, which are: Prox.77 and Prox.2010, is corrected based on systematic studying on 60 of fusion reactions. The correction in γ is caused to improve agreeing fusion cross sections with empirical amounts of them specifically in sub-barrier energies. This correction has significant effect on increasing the theoretical amounts of cross sections in the range of Coulomb sub-barrier energies. The produced results show improvement of agreement on theoretical amounts of Coulomb barrier height with corresponding laboratory data in the various collision systems. In addition, the obtained results show that the MP.2010 potential is able to produce laboratory data more accurate rather than other introduced potentials.     

234U裂变的五维势能曲面计算

本工作基于连接二次曲面的形状描述+LSD(Lublin Strasbourg drop)公式+折叠汤川势建立了宏观 微观模型。对234U裂变,计算了具有5 906 250个格点的五维势能曲面,然后通过搜索势能曲面得到了对称裂变和非对称裂变两个裂变通道,给出了裂变势垒高度以及鞍点和断点等特殊位置的原子核形状。     

Peregrinations on cold fusion

Attention is focused on the possibility of resonance-enhanced deuteron Coulomb barrier penetration. Because of the many-body nature of the interactions of room-temperature deuterons diffusing through a lattice possessing deuterons in many of the interstitial positions, the diffusing deuterons can resonate on the atomic scale in the potential wells bounded by the ascending walls of adjacent Coulomb barriers and thereby penetrate the Coulomb barriers in a fashion vastly underestimated by two-body calculations in which wells for possible resonance are absent. Indeed, perhaps the lack of robust reproducibility in cold fusion originates from the narrowness of such transmission resonances.     

Yield from Proton-Induced Reaction on Light Element Isotopes in the Hydrogen Plasma Focus

The high Q-value of some (p,α) fusion reactions is very important in the investigation that can lead to power production with controlled fusion using advanced fuels (hydrogen-lithium-7, hydrogen-boron-11). For this reason, it is crucial to know the rates of these fusion reactions. Unfortunately, in the fusion machines such as plasma focus device, the interaction energy is usually far below the Coulomb barrier. Because of that, direct measurements of the relevant reaction cross sections are practically impossible. A few different indirect approaches have been proposed. In this work the Trojan Horse Method (THM) will be described. On the basis of the results obtained from the THM method and data, which are well-known from our previous work (Banjanac et al. in Radiat Meas 40:483–485, 2005), the reaction rate for proton-induced reaction ⁷Li(p,α)α produced in the hydrogen plasma focus is calculated. This calculation will be compared with the measurements of α particles production rate using CR-39 detectors.