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.     

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.     

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 ＋^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.     

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.     

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.     

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 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)2α reaction channel. The (n,2n)2α reaction channel is achieved through sixdifferent reaction approach, which are illustrated in this paper. The calculated results agree very well with the measured data at E_n = 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.     

Double-Differential Cross Section of 5He Emission

The probability of ⁵He particle emission has been affirmed theoretically [J.S. Zhang, Science in China G47 (2004) 137]. In order to describe the ⁵He emission, the theoretical formula of the double-differential cross section of emitted ⁵He is to be established. Based on the pick-up mechanism, used for calculating the formula of d, t, ³He, α emissions, the theoretical formula of double-differential cross section of ⁵He is obtained, which is expressed in the form of Legendre coefficients. In the case of low incident energies, the configuration [J.S. Zhang, Science in China G47 (2004) 137; J.S. Zhang, Commun. Theor. Phys. (Beijing, China) 39 (2003) 83] is the dominant part in the reaction processes. The calculated result indicates that the forward peaked angular distribution of the composite particle emission is weaker than that of the emitted single nucleon due to pick-up nucleon from the Fermi sea. As an example, the reactions of n+¹⁴N have been calculated, and the Legendre coefficients of d, t, ³He, α, ⁵He emissions are obtained respectively. The results show that the forward tendency is decided by the average momentum per nucleon in the emitted composite particles. The larger the average momentum is, the stronger the forward tendency is.     

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。     

14MeV钕的同位素反应截面的测量

报道了在13.5—14.6MeV中子能区用活化法以⁹³Nb(n,2n)^92mNb反应截面为中子注量标准测得的¹⁵⁰Nd(n,2n)¹⁴⁹Nd,¹⁴⁸Nd(n,2n)¹⁴⁷Nd和¹⁴²Nd(n,2n)¹⁴¹Nd的反应截面值.由13.5±0.2,14.1±0.1和14.6±0.2MeV中子引起的¹⁵⁰Nd(n,2n)¹⁴⁹Nd反应截面值分别为2037±85,1737±68,1657±65mb,¹⁴⁸Nd(n,2n)¹⁴⁷Nd反应截面值分别为1394±58,1416±54,1956±76mb,^{142Nd(n,2n)141Nd反应截面值分别为1501±59,1623±62,1764±111mb.单能中子由T(d,n)4He反应获得.文中还收集了已发表的数据以作比较.}     

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.      

n+11B反应的理论计算和分析

在统一的豪泽–费许巴赫理论和激子模型的基础上,利用光学模型来处理中子诱发轻核核反应的一种新理论已经产生.利用这一新理论,对当入射中子En≤20MeV时n+¹¹B反应的所有反应截面,出射中子和α粒子的双微分截面进行了计算.通过比较理论计算的各种截面,出射中子总的双微分截面与实验数据,可以认为这一理论模型处理轻核核反应是很成功的.     

14MeV中子引起的核反应截面测量中监督反应的研究

讨论了14MeV中子引起的核反应截面测量中监督反应对测量结果的影响,同时列出了常用的一些监督反应及参数,利用截面的评价值给出了一些监督反应的截面随中子能量变化的关系曲线,并对^27Al（n,p）^27Mg反应做了定性分析,说明了监督反应的选取对反应截面测量的重要性。 It was discussed in this article that the effects of different monitors in the cross section measurements of nuclear reactions induced by 14 MeV neutrons, at the same time some monitors and correlative parameters were listed. The excitation functions of monitors are taken from the evaluatied cross sections, and a qualitative analysis has been performed for ^27Al（n,p） ^27Mg reaction. It indicates that the choice of monitor is very important for cross section measurements     

Theoretical analysis of double-differential neutron emission cross sections for n+56Fe reactions at incident energies of 7-13 MeV

The double-differential neutron emission cross sections for n+56Fe reactions at incident energies of 7-13 MeV at different angles are calculated by the UNF(abbreviation for unified,2009 Version)code,which is based on the unified Hauser-Feshbach and exciton model.The results indicate that the higher the incident energies,the better the results,although there are some discrepancies between the calculated results and the measured data for natural iron.These discrepancies are analyzed in detail in this paper.In addition,the calculated results are also compared with the evaluated results of ENDF/B VII.O and JEFF-3.1.1 near the angle of 90°at incident energies of 8.17 and 11.5 MeV,respectively.     

13.5—14.6MeV中子能区镓的同位素反应截面的测量

报道了在13.5—14.6MeV中子能区用活化法以⁹³Nb(n,2n)^92mNb反应截面为中子注量标准测得的⁶⁹Ga(n,2n)⁶⁸Ga,⁶⁹Ga(n,p)^69mZn,⁷¹Ga(n,p)^71mZn和⁷¹Ga(n,n′α)⁶⁷Cu的反应截面值.由(13.5±0.2),(14.1±0.1)和(14.6±0.2)MeV中子引起的⁶⁹Ga(n,2n)68Ga反应截面值分别为(794±31),(869±35)和(986±39)mb,⁷¹Ga(n,n′α)⁶⁷Cu反应截面值分别为(1.3±0.1),(1.7±0.1)和(2.5±0.1)mb.在中子能量为(14.1±0.1)MeV能量点,⁶⁹Ga(n,p)^69mZn反应截面值为(21.5±1.0)mb,⁷¹Ga(n,p)^71mZn反应截面值为(12.4±0.7)mb.单能中子由T(d,n)⁴He反应获得.文中还列举了尽可能收集到的数据以作比较.     

标量介子场对(ΩΩ)(0+)态生成截面的计算

研究了Ω+Ω→(ΩΩ)0++σ(ε)过程生成(ΩΩ)0+双重子态的截面.结果表明这个过程的生成截面比已计算过的其他Ω+Ω→(ΩΩ)0++X(赝标介子或矢量介子)过程的截面要大一至两个量级.因此这可能是一个值得考虑的(ΩΩ)0+生成途径.     

轻核(n,x)反应微分截面的实验测量

对本课题组十几年来的(n,x)反应实验研究工作进行了评述.介绍了屏栅电离室的特点、构造与工作原理.用屏栅电离室在北京大学4.5MV静电加速器上测量了1—7MeV中子6Li(n,t)4He和10B(n,α)7Li反应的微分截面与截面,对实验结果进行了讨论. Our research work on (n, x) reaction for more than one decade is reviewed. The characteristics, structure, and working principle of the gridded ionization chamber are discussed. Differential cross sections and cross sections of the~(6)Li(n, t)~(4)He and~(10)B(n, α)~(7)Li reactions were measured in the neutron energy range of 1—7 MeV by using the GIC method. Experiments were carried out at the 4.5 MV Van de Graaff accelerator of Peking University. Results of the measurement are discussed.