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.     

^5He Emission in Neutron-Induced ^10B Reactions

In n ＋^10B reactions, ^5He cluster emission has been discussed with the updated level scheme and the new optical model parameters. In this paper the reaction channels related to ^5He emission are listed in detail. By using the new reaction model for light nuclei, the double-differential cross sections of total outgoing neutrons for n ＋ ^10 B reactions at En= 14.2 MeV have been calculated, and the results agree fairly well with the measurements. Particularly, in the energy-angular spectra the contribution from the 5He-emission to the total outgoing neutron double-differential cross sections has also been analyzed, and the partial energy-angular spectra of 60° at En= 14.2 MeV have been given. The calculated results indicate that once the 5He emission is taken into account, the fitting with the double-differential measurements of total outgoing neutrons at the low energy region could be improved. Therefore, to consider the ^5He emission properly in the reaction processes of light nuclei is necessary.     

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.     

Single-Proton Pickup Reaction of the Halo Nucleus ^6He on a ^9Be Target at 25 MeV/nucleon

The inclusive differential cross sections of the ^7 Li nucleus in a reaction induced by ^6He on a ^9Be target are measured at an incident energy of 25 MeV/nucleon. Finite-range distorted-wave Born approximation calculations suggest that these ^7 Li particles are formed in a direct single-proton pickup reaction ^9Be（^6He,^7 Li）^8Li. The experimental data can be well reproduced by taking into account of the contributions of both the ground states and the first excited states of ^7Li and ^8Li.     

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.     

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.     

Measurement of ^2H（^8Li, ^9Be）n Reaction Relevant to Primordial Nucleosynthesis

The angular distribution of the ^2H（^8Li, ^9Be）n （ground state） reaction, important to primordial nucleosynthesis in the inhomogeneous model, has been measured at E = 8.1 MeV using a secondary ^8Li beam. Cross section of this reaction was determined to be 9.0 4±3.4 mb. According to the cross section, the astrophysical S-factor was calculated to be 272 4±103 keV b. It is shown that ^2H（8^Li, ^9Be）n （ground state） reaction is important for creating 9Be, but less important for destroying aLl in primordial nucleosynthesis.     

Isoscaling Behavior in ^48,40Ca＋^9Be Collisions at Intermediate Energy Investigated by the HIPSE Model

The fragment production cross sections for 140 Me V/nucleon ^48,40 Ca^＋9 Be reactions are calculated by the heavyion phase space exploration （HIPSE） model. Isoscaling behavior is observed. The isoscaling parameters a and β for both heavy and light fragments from the HIPSE model calculations are in good agreement with the experimental data. It is shown that the potential parameters in the HIPSE model have very little effect on the isoscaling parameters. The effect of the excitation energy and evaporation on the isoscaling behavior is also discussed.     

Investigation of neutron induced reactions on ^23Na by using Talys1.4

The neutron induced reactions on ^23Na are investigated by using the Talys1.4 program. The calculated results for the ^23Na（n, 2n）22Na reaction are found to agree with the experimental results. The cross sections of the residues of the（n, n）,（n, γ）,（n, p）, and（n, np） channels in the reactions are presented, and at the same time, the neutron induced reactions on22 Ne are also investigated.     

Ab initio calculations on the spectroscopic constants, vibrational levels and classical turning points for the 21∏u state of dimer 7Li2

The accurate dissociation energy and harmonic frequency for the highly excited 2^1Пu state of dimer ^7Li2 have been calculated using a symmetry-adapted-cluster configuration-interaction method in complete active space. The calculated results are in excellent agreement with experimental measurements. The potential energy curves at numerous basis sets for this state are obtained over a wide internuclear separation range from about 2.4a0 to 37.0a0. And the conclusion is gained that the basis set 6-311＋＋G（d,p） is a most suitable one. The calculated spectroscopic constants De, Re, ωe, ωeχe, ae and Be at 6-311＋＋G（d,p） are 0.9670 eV, 0.3125 nm, 238.6 cm^-1, 1.3705 cm^-1, 0.0039 cm^-1 and 0.4921 cm^-1, respectively. The vibrational levels are calculated by solving the radial SchrSdinger equation of nuclear motion. A total of 53 vibrational levels are found and reported for the first time. The classical turning points have been computed. Comparing with the measurements, in which only the first nine vibrational levels have been obtained so far, the present calculations are very encouraging. A careful comparison of the present results of the parameters De and We with those obtained from previous theories clearly shows that the present calculations are much closer to the measurements than previous theoretical results, thus representing an improvement on the accuracy of the ab initio calculations of the potentials for this state.     

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     

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.     

Quasi-classical Trajectory Study of Reaction O （^3P）＋HCl （v =2; j=1,6,9） →OH＋Cl

The reaction O（^3P）＋HCl （v=2; j= 1,6,9） → OH＋Cl is theoretically studied with a quasi-classical trajectory method （QCT） on the benchmark potential energy surface of the ground 3A＇＇ state [J. Chem. Phys. 119（2003）9550]. The QCT-calculated state-resolved rotational distributions are in good agreement with the experimental results. The rotational polarization of the product OH molecule becomes weaker as the initial HCl rotation is excited. The calculated results can be explained from the large mass factor cos2 β of the title reaction, the van der Waals well in the potential energy surface and the secondary encounters in the exit channel.     

Test of Determination of (p,γ) Astrophysical S-Factors Using the Asymptotic Normalization Coefficients from Neutron Transfer Reactions

The asymptotic normalization coefficients （ANCs） for the virtual decay ^17 O→^16 O＋n are derived from the angular distributions of the 16 O（d, p）^17O reaction leading to the ground and first excited states of ^17O, respectively, using the distorted wave Born approximation and the adiabatic wave approximation. The ANCs of ^17F are then extracted according to charge symmetry of mirror nuclei and used to calculate the astrophysical S-factors of ^16 O（p, γ）^17 F leading to the first two states of ^17 F. The present results are in good agreement with those from the direct measurement. This provides a test of this indirect method to determine direct astrophysical S-factors of （P, γ） reaction. In addition, the S-factors at zero energy for the direct captures to the ground and first excited states of ^17 F are presented, without the uncertainty associated with the extrapolation from higher energies in direct measurement.     

Possible Way to Synthesize Superheavy Element Z=117

Within the framework of the dinuclear system model, the production of superheavy element Z = 117 in possible projectile-target combinations is analysed systematically. The calculated results show that the production cross sections are strongly dependent on the reaction systems. Optimal combinations, corresponding excitation energies and evaporation channels are proposed, such as the isotopes^248.249 Bk in ^48 Ca induced reactions in 3n evaporation channels and the reactions ^45Sc＋246.248Cm in 3n and 4n channels, and the system ^51 V＋ 244pu in 3n channel.     

The Main Path to C, N, O Elements in Big Bang Nucleosynthesis

The production of C, N, O elements in a standard big bang nucleosynthesis scenario is investigated. Using the up-to-date data of nuclear reactions in BBN, in particular the ^8Li （n,γ） ^9Li which has been measured in China Institute of Atomic Energy, a full nucleosynthesis network calculation of BBN is carried out. Our calculation results show that the abundance of 12 C is increased for an order of magnitude after addition of the reaction chain ^8Li（n,γ） ^9Li（α,n） ^12B（β） ^12C, which was neglected in previous studies. We find that this sequence provides the main channel to convert the light elements into C, N, O in standard BBN.     

Fusion Hindrance Factor of Heavy Nuclei Extracted from Experimental Data

The reactions of ^16O＋^204pb, ^82Se＋^138Ba and ^96Zr＋^124Sn lead to the same compound nucleus ^220Th. In terms of the assumption that the surviving probability is independent of entrance channel, we have extracted the fusion hindrance factor from the evaporation residue cross sections for the reactions of ^82Se＋^138 Ba and ^96Zr＋^124Sn and compared with the results calculated using a two-parameter Smoluchowski equation. The theoretical predictions are basically in agreement with the experimental data. It is found that the probability of forming a compact ^220Th is less than 10% for the reactions considered. For the systems more massive than ^220Th, fusion should be much more strongly suppressed due to the competition of quasifission with complete fusion. Understanding of this inhibition is essential to forming new superheavy nuclei.     

Coupled—Channel Investigation of Collisions of Protons and Antiprotons with Hydrogen Atoms in the 2p States

The impact parameter method is used to calculate the inelastic scattering cross sections of protons and antiprotons,which raise hydrogen atoms from the 2p states to the n=3 states.The calculation involves the n=1,2,3 states of the target and covers the energy range from 3keV to 2500keV.The study of the influence of the sign of the projectile charge is the main target of this investigation.Therefore,the exchange effects in the case of proton-induced reactions are ignored.The results of the calculations are in reasonable agreement with a previous work.     

Effects of the vibrational and rotational excitation of reagent on the stereodynamics of the reaction S（3P） + H2→ SH + H

Quasiclassical trajectory （QCT） calculations are first carried out to study the stereodynamics of the S （3p） ＋ H2 → SH ＋ H reaction based on the ab initio 13Atr potential energy surface （PES） （Lii etal. 2012 J. Chem. Phys. 136 094308）. The QCT-calculated reaction probabilities and cross sections for the S ＋ H2 （v = 0, j = 0） reaction are in good agreement with the previous quantum mechanics （QM） results. The vector properties including the alignment, orientation, and polarization- dependent differential cross sections （PDDCSs） of the product SH are presented at a collision energy of 1.8 eV. The effects of the vibrational and rotational excitations of reagent on the stereodynamics are also investigated and discussed in the present work. The calculated QCT results indicate that the vibrational and rotational excitations of reagent play an important role in determining the stereodynamic properties of the title reaction.