~ 5he Pre-equilibrium Emission Double Differential Cross Sections And Neutron ~ (14) N Reaction Double Differential Cross Sections For The Establishment Of The Document

In recent years, the total outgoing neutron double-differential cross sections of neutron induced light nuclear reactions have been calculated by using a new nuclear reaction model. In these researches, the possibility of 5He emission was revealed. In order to describe the ⁵He emission, the theoretical formula of the double-differential cross section of ⁵He emission needs to be established. Based on the pick-up mechanism in pre-equilibrium emission processes, used for calculating the formula of d, t, ³He andαemissions, the theoretical formula of double-differential cross section of ⁵He is obtained, which complete the description of the double-differential cross section of composite particle emissions in the pre-equilibrium statistical model.In the case of low incident energies, the configuration [1, 4] is the dominant part in the reaction processes, which means one nucleon above the Fermi sea and the others in the Fermi sea. The calculated results indicate that for a composite particle, the higher of the incident energy is, the stronger of the forward tendency is. When there is the same incident energy, the forward tendency of a composite particle is weaker than the single particle's. This is because of the motion of the nucleons in the Fermi sea is isotropic; the picked-up particles should counteract the forward tendency of the outgoing single particle. The calculated results show that the forward tendency is determined by the average momentum per nucleon in the emitted composite particles. The larger of the average momentum is, the stronger of the forward tendency is. Besides the reason mentioned above, the forward tendency also depends on the form of integrated factor.As an example, the reactions of n＋¹⁴N have been calculated; the results show that the forward tendency of ⁵He is stronger than that of theαparticle but weaker than the single neutron's. ⁵He is unstable, it will be separated into one neutron and oneα-particle spontaneously. The double-differential cross sections of the outgoing neutron and theα-particle in the center of mass system have been calculated, the results show that the energy ranges of the outgoing neutron and the a-particle spectra contribute to the low energy spectrum in the total outgoing energy spectrum.By using a new reaction model for the 1-p shell light nuclei, the double-differential cross sections of n＋¹⁴N reactions have been analyzed. This new model keeps angular momentum and parity conservation properly in the pre-equilibrium emission. Meanwhile, the energy balance for variety particles emission is strictly considered by the accurate kinematics. The calculated results agree fairly with the double-differential measurements. It is affirmed that the new model is able to describe the behavior of 1-p shell light nuclear reactions well.Based on the new model, the LUNF code has been established. Using the LUNF code, the double-differential cross sections of n＋¹⁴N reactions have been calculated. The reaction mechanism of n＋¹⁴N is very complex, there are more than one hundred partial reaction channels opened even at incident neutron energy of 14.2MeV. In the model calculation, all the residual states are discrete levels without continuous state. The particle emissions from the compound nucleus to the residual nuclei's discrete levels in pre-equilibrium mechanism are taken into account with the angular momentum and parity conservation. ⁵He emission in the n＋¹⁴N reaction has been considered, when the incident energy is high, the neutron from the ⁵He separating contributes to the total outgoing neutron energy spectra in the low energy region.In the case of n＋¹⁴N reaction, the pre-equilibrium mechanism dominates the whole reaction processes, which is the same as other 1-p shell light nuclei, like ^6,7Li, ¹⁰B, ¹⁰C, and ¹⁶O. Thus, only the equilibrium theory could not work well, like Hauser-Feshbach model, of the 1-p shell light nuclear reaction. Meanwhile, from the comparison of the outgoing neutron angular-energy spactra obtained by using this new model and Kalbach Systematics, the results of the comparison indicate that the Kalbach Systematics could not give the correct energy spectrum of the outgoing particles. For the 1-p shell light nucleus, the mass of the compound nucleus is so light that the recoil effect of the particle emission is very strong. Thus, the accurate kinemics plays an important role, which not only keeps the energy balance, but also to produce the correct shapes of the partial outgoing spectra in the secondary particle emission processes for reproducing the double-differential measurements. Therefore, the accurate kinemics is the one of the key point to set up file-6 for double-differential cross sections in the neutron library with full energy balance.Lack of suitable theoretical method, there is no files-6 for double-differential cross sections of ¹⁴N in the worldwide neutron data libraries. Now, a light nuclear reaction model is proposed, and the LUNF code is developed accordingly. In terms of fitting the experiment measured data with LUNF code, the files-6 for double-differential cross sections of n＋¹⁴N reactions at incident energies up to 30MeV have been established in the ENDF format. And utilizing the data in the ENDF/B-Ⅵneutron library, the total file of neutron induced ¹⁴N reactions including file-6 for double-differential cross sections in the energy range 10^-5eV to 30MeV can be established, which could provide the application in the nuclear engineering.