Calculation of Double—Differential Cross Sections of n＋^7Li Reactions Below 20 MeV

A new reaction model for light nuclei is proposed to analyze the measured data,especially for analysis of the double-differential cross sections of the outgoing particles.Many channels arc opened in the n + 7Li reaction below En＜ 20 MeV.The reaction mechanism is very complex,beside the sequential emissions there are also three-body breakup processes.Because of a strong recoil effect of light nucleus reactions,the energy balance is strictly taken into account.The comparisons of the calculated results with the double-differential measurements indicate that the model calculations are successful for the total outgoing neutrons.     

Theoretical Analysis of Neutron Double-Differential Cross Section of n+10B at 14.2 MeV

By using a new reaction model for light nuclei, the double-differential cross sections of n+ 10B reactions atEn ＝ 14.2 MeV have been analyzed. In the case of n+10B reactions there are over one hundred opened partial reactionchannels. Besides the sequential particle emissions, there is also the three-body breakup process, in which the kinematicsis classified into four types. In this paper the opened reaction channels are listed in detail with the LUNF code, withwhich the model calculation is performed to analyze the total outgoing neutron double-differential cross sections. All ofthe fittings agree fairly well with the measurements. The calculation results indicate that the pre-equilibrium mechanismdominates the whole reaction processes, and the recoil effect in light nuclear reaction is essentially important.     

Theoretical Analysis of Neutron Double-Differential Cross Section of n+11B at 14.2 MeV

A new reaction model for light nuclei is proposed to analyze the measured data, especially for the doubledifferential cross sections. In this paper the calculation with this model is employed to analyze measurements of the total outgoing neutron double-differential cross sections for n+11B reactions at En = 14.2 MeV. The representation of the double-differential cross sections of the second emitted particles is given in detail. The calculation results indicate that the recoil effect in light nuclear reaction is essentially important. The reaction channels are discussed in detail.     

Analysis of Neutron Double-Differential Cross Section of n+14N at 14.2 MeV

By using a new reaction model for light nuclei, the double-differential cross section of n 14N reactions at En = 14.2 MeV has been analyzed. In the case of n 14N reactions, the reaction mechanism is very complex, there are over one hundred opened partial reaction channels even at incident energy En = 14.2 MeV. In this paper the opened reaction channels are listed in detail. With LUNF code the model calculation is performed to analyze the doubledifferential cross sections of total outgoing neutron. The calculated results agree fairly with the experimental data. The results indicate that the pre-equilibrium mechanism dominates the whole reaction processes, and the recoil effect in light nuclear reactions is essentially important. 5He emission has been considered, but it is only a small contribution to the double-differential cross section at incident energy En = 14.2 MeV.     

Theoretical Analysis of Neutron Double-Differential Cross Sections of n ＋^9Be Reactions

By using the nuclear reaction model for light nuclei, the calculations of the double-differential cross sections of outgoing neutrons from n ＋^9Be reactions are performed. The total outgoing neutrons are only come from the （n, 2n）2a reaction channel. The （n, 2n）2a reaction channel is achieved through six different reaction approach, which are illustrated in this paper. The calculated results agree very well with the measured data at En = 7.1, 8.09, 8.17, 9.09, 9.97 and 10.26 MeV, because the updated level schemes related to the n ＋ ^9Be reactions have been employed in this calculations.     

Theoretical Analysis of Neutron Double-Differential Cross Section of n ＋^19F at 14.2 MeV

A new light nuclear reaction model has been developed and the double-differential measurements of lp shell nuclei have been analyzed successfully. Now, the application of this model is expanded to 19F of the 2s-ld shell nucleus. The double-differential cross section of total outgoing neutron for n ＋^19F reactions at En=14.2 MeV has been calculated and analyzed, which agrees fairly well with the experimental measurements. In this paper, the contributions from different reaction channels to the double-differential cross sections have been analyzed in detail. The calculations indicate that this light nudear reaction model is also able to be used for the 2s-ld shell nucleus so long as the related level scheme couM be provided sufficiently.     

Analysis of Neutron Double-Differential Cross Section of n＋^14N at 14.2 MeV

Abstract By using a new reaction model for light nuclei, the double-differential cross section of n ^14N reactions at En=14.2 MeV has been analyzed. In the case of n ^14N reactions, the reaction mechanism is very complex, there are over one hundred opened partial reaction channels even at incident energy En=14.2 MeV. In this paper the opened reaction channels are listed in detail. With LUNF code the model calculation is performed to analyze the doubledifferential cross sections of total outgoing neutron. The calculated results agree fairly with the experimental data. The results indicate that the pre-equilibrium mechanism dominates the whole reaction processes, and the recoil egect in light nuclear reactions is essentially important. 5He emission has been considered, but it is only a small contribution to thedouble-differential cross section at incident energy En=14.2 MeV.     

Analysis of Neutron Double-Differential Cross Sections for n + 12C Reaction Below 30 MeV

Based on the light nucleus reaction model (Nucl. Sci. Eng. l33 (1999) 218), four aspects (neutron incident energy region, reaction channel analysis, the renewed level schemes and the optical model parameters) of n 12 C reaction are improved to calculate total outgoing neutron double-differential cross sections with modified LUNF code below 30 MeV. The calculated results agree fairly well with the experimental data at En = 14.1 MeV and 18 MeV. The analysis shows that the pre-equilibrium mechanism, which is exactly considered the conservation of energy, momentum and parity, dominates the whole reaction process. The contribution of the neutron emission from 5He to total energyangular spectra is also considered properly. This modified LUNF code will be a useful tool to set up the file of neutron double-differential cross sections below 30 MeV in the neutron evaluation nuclear data library.     

Further Analysis of Neutron Double-Differential Cross Section of n ＋ ^16O at 14.1 MeV and 18 MeV

By using a new reaction model for light nuclei, the double-differential cross section of total outgoing neutron with LUNF code for n＋^16O reactions at En=14.1 MeV and 18 MeV have been calculated and analyzed. In this paper the opened reaction channels, which have contribution to emitting the neutrons, are listed in detail. To improve the fitting results the direct inelastic scattering mechanism is involved. The calculating results agree fairly well with the experimental data at E,~ = 14.1 MeV and the deviation from calculated results and experimental data in low energy region at En= 18 MeV has been analyzed. Since the possibility of 5He has been affirmed theoretically [J.S. Zhang, Sci. Chin. G 47 （2004） 137], so 5He emission from n＋ ^16O reaction is taken into account, which plays an important role at the region of the outgoing neutron energy εn〈3 MeV in total outgoing neutron energy-angular spectrum. The calculated results indicate that the pre-equilibrium mechanism dominates the whole reaction processes, and the recoil effect in light nuclear reactions is essentially important.     

Analysis of Neutron Double-Differential Cross Sections for n ＋ ^12 C Reaction Below 30 MeV

Based on the light nucleus reaction model （Nucl. Sci. Eng. 133 （1999） 218）, four aspects （neutron incident energy region, reaction channel analysis, the renewed level schemes and the optical model parameters） of n＋ ^12 C reaction are improved to calculate total outgoing neutron double-dilferential cross sections with modified LUNF code below 30 MeV. The calculated results agree fairly well with the experimental data at En = 14.1 MeV and 18 MeV. The analysis shows that the pre-equilibrium mechanism, which is exactly considered the conservation of energy, momentum and parity, dominates the whole reaction process. The contribution of the neutron emission from 5He to total energy- angular spectra is also considered properly. This modified LUNF code will be a useful tool to set up the file of neutron double-differential crass sections below 30 Me V in the neutron evaluation nuclear data library.     

Absolute Cross Sections for some Reactions Induced by Differential Neutron Flux

The measurements of activation cross sections for some reactions induced by a differential neutron flux of (D-T) compact neutrons generator were discussed. The comparison of measured cross sections with those averages calculated from the energy cross section curves found in the literature gives good agreement. The used thin targets were prepared under vacuum by both evaporation and sputtering techniques.     

19F+93Nb耗散反应产物激发函数中截面测量的不重复性

完成了¹⁹F+⁹³Nb重离子耗散碰撞激发函数的两次独立测量.束流的入射能量为100—108MeV,步长250keV.两次测量的宏观条件几乎完全一样,惟一的差别是使用了厚度分别为70和71μg/cm²的两块⁹³Nb同位素靶.实验结果表明:(1)两次测量所得到的耗散反应产物激发函数的涨落具有不可平滑的结构;(2)这种不平滑的涨落截面有不重复的迹象.着重从实验的角度对这一结果进行了讨论.     

14MeV中子引起的185Re(n,2n)184g,mRe和191Ir(n,2n)190Ir的核反应截面测量

利用活化方法测量了1?4MeV中子引起的¹⁸⁵Re(n,2n)^184gRe,¹⁸⁵Re(n,2n)^184mRe和¹⁹¹Ir(n,2n)¹⁹⁰Ir核反应的截面.中子能量E_n=(14.7±0.2)MeV时的实验结果分别为:(1817±85)mb,(390±18)mb和(2038±82)mb.并利用HFTT程序计算了中子能量在7—18MeV范围内的截面值,给出了其中两个核反应的激发函数曲线.     

8.19 MeV中子与9Be作用的次级中子双微分截面测量

用中国原子能科学研究院HI13串列加速器上的多探测器快中子飞行时间谱仪, 测量了8.19 MeV中子与9Be作用时, 从20°到160°区间26个角度的次级中子双微分截面。测量截面以np散射截面作为标准进行归一。实验结果用Monte Carlo方法进行了中子注量率衰减、多次散射和有限几何修正, 并用MCNP4C程序对所用的Monte Carlo程序进行了验证。测量结果与评价数据以及其它实验室的数据进行了比较。The secondary neutron emission double differential cross section of 9Be induced by 8.19 MeV neutron was measured at 26 different angles from 20°to 150°by using the multi detector fast neutron TOF spectrometer at the HI 13 Tandem Accelerator at China Institute of Atomic Energy(CIAE). The results were normalized to np scattering measurement. A special Monte Carlo code which was validated with the MCNP 4C code was employed to analyze the measured data for the corrections of neutron flux attenuation, multiple scattering and finite geometry. The measured results were compared with the evaluated data and the other measurements.      

中子与52Cr反应截面的理论分析

根据中子与天然核Cr及其同位素反应的总截面,去弹性散射截面和弹性散射角分布的实验数据,获得了入射中子能量从1MeV—250MeV的一组普适中子与Cr及其同位素反应的光学模型势参数.应用光学模型,扭曲波玻恩近似理论,宽度涨落修正的Hauser-Feshbach理论,和预平衡反应的激子模型,计算和分析了中子与⁵²Cr反应的所有截面、角分布、能谱和双微分截面.理论计算与实验数据进行了分析比较.     

80MeV/u 20Ne轰击9Be碎裂产物反应总截面的测量

介绍了用透射法测量中能区²⁰Ne打⁹Be靶碎裂产生的次级束与Si靶作用的核反应总截面的方法,以及实验的探测器布局、实验过程和实验结果.并对理论上预言有奇异结构的核¹²N,¹⁷Ne和¹⁷F的实验结果与其相邻核进行了比较.     

热熔合反应合成超重核产生截面的同位素依赖性

通过在形成超重核的重离子俘获和熔合过程中引入位垒分布函数的方法对双核模型做了进一步发展. 超重核形成过程中的俘获、熔合和蒸发3个阶段分别采用了半经验的耦合道模型、数值求解主方程和统计蒸发模型的方法来描述. 计算了近年来Dubna小组利用热熔合反应⁴⁸Ca(²⁴³Am, 3n—5n)^288—286115和⁴⁸Ca(²⁴⁸Cm, 3n—5n)^293—291116合成超重新核素的蒸发余核激发函数. 系统分析了⁴⁸Ca轰击锕系元素U,Np,Pu,Am,Cm合成超重核Z=112—116产生截面的同位素依赖性. 给出了合成超重新核素最佳的弹靶组合和入射能量, 即有最大的超重核产生截面. 计算说明, 壳修正能和中子分离能是影响超重核生成截面产生同位素依赖性的主要因素.     

中子诱发16O双微分截面的理论分析

应用已经发展的轻核反应新模型理论,计算和分析了中子诱发^16O反应截面,比较和分析了出射中子双微分截面的理论计算结果和实验数据,从理论计算结果与实验的符合情况看,这一理论和方法对于计算轻核的双微分截面是成功的。     

19F+93Nb重离子耗散碰撞中截面测量的不可重复性

完成了¹⁹F+⁹³Nb重离子耗散碰撞激发函数的两次独立测量.束流¹⁹F⁸⁺的入射能量100—108MeV,能量步长250keV;两次测量中分别使用了厚度为70和71μg/cm²的⁹³Nb靶,其它宏观实验条件(例如,入射能量及能量步长,探测器及其探测角度,加速器、电子学以及数据获取系统的参数选取等等)则保持完全相同.实验结果表明,两次测量所得到的耗散产物截面的激发函数的不平滑结构具有不可重复性.这一实验结果支持了最近提出的理论预言:“在复杂量子碰撞中存在对初始条件的极端敏感性与混沌运动.”