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 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.     

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.     

Measurement of One— and Two—Neutron Transfers in Reaction of ^6He＋^9Be at 25MeV／u

The cross sections one-and two-neutron transfers induced by 6He at 25MeV/u on a^9Be target were measured in RIKEN.Clear identification of the recoiled Be isotopes was achieved.In total five 11Be and 371 ^10Be events,the corresponding two-and one-neutron transfers were obtained and analysed for transfer reaction cross sections.The results are useful to determine the spectroscopic factors of the internal halo structure of the 6He nucleus.     

Medium Influence of the Nucleon—Nucleon Cross Section on the Fragmentation

Based on an isospin-dependent quantum molecular dynamics model we studied the influence of a medium correction of an isospin-dependent nucleon-nucleon cross section on the fragmentation at the intermediate energy heavy-ion collisions. We found that the medium correction from an isospin-dependent nucleon-nucleon cross section, at the same time, the momentum-dependent interaction also produces an important role for enhancing the influence of the medium correction on the isospin effect of two-body collisions in the fragmentation process.     

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.     

Angular Distribution and Angular Dispersion in Collision of ^19F＋^27Al at 114 MeV

Angular distributions of fragments B, C, N, O, F, Ne, Na, Mg and Al induced by the collision of ^19F ^27Al at 114 MeV have been measured. Angular dispersion parameters are extracted from the experimental data and compared with the theoretical ones. The dynamic dispersions for dissipative products depend strongly on the charge number Z of the fragments.     

Measurement of the Breakup Cross Sections in ^6He＋^9Be Reaction at 25 MeV／Nucleon

The breakup reaction cross sections were measured for the reaction of^6He at 25 MeV/nucleon from ^9Be target with intensity of 10^5 pps. By fitting the energy spectra of breakup α particles with Gaussian functions, the angular distribution of differential cross sections in the laboratory system has been extracted and compared with the Serber model calculations. The good agreement between the calculation and the experimental data favours a dominant configuration of the ^4He core plus valence neutrons for the structure of^6He.     

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 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.     

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.     

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.     

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.