Measurement And Analysis Of The Double-differential Cross Sections Of Secondary Neutrons For ~9Be At 21.65 MeV Incident Neutrons

The neutron emission double-differential cross sections(DDXs) is one of the mostimportant nuclear data used in nuclear engineering design and in the study of nuclearreactions mechanism.In this thesis the measurement of the DDXs of the neutron emissioncross sections have been described in detail for ~9Be at the incident neutron energy of 21.65MeV and the measurement results have been analyzed with a new light nuclear reactionmodel.Special attention has been paid to the neutron data between 20 to 200 MeV due to thedevelopment of ADS and other neutron application fields such as dosimetry for radiationsafety and fast neutron cancer therapy in recent years.Meanwhile,more precise nucleardata,not only nuclear data but also energy and angular distributions are required by thedevelopment of nuclear engineering.However,the experimental and evaluation data arevery sparse.Up to now,most of the DDX measurements performed are at around 14 MeV,while the DDX measurements are very scarce above 20 MeV.On the other hand the resultsof theoretical calculation are discrepant from each other with different light nuclear reactionmodels.Therefore,DDX measurement is necessary for checking and improving nuclearreaction models and evaluation nuclear data file at different energy region.Nowadaysavailable nuclear reaction models are mainly employed to calculate the DDXs for themedium-heavy mass,as well as the fissile nuclei,and in these codes the reaction process isonly the sequential particle emissions processes is considered,which could not be appliedto describe of the neutron induced reactions for light nuclei.For this reasons,it is necessaryto establish and develop a new nuclear model for light nuclei and to measure doubledifferential cross sections precisely for some key nuclei at above 20 MeV regions.Beryllium has been considered as an important material for the thermonuclear reactorsIt often served as the neutron multiplifier in fusion reactors,because of the relatively large(n,2n) cross section,low mass and low neutron-capture cross section.There is no suitablereaction model for the light nucleus at the mass number about 10 regions,which is too lightfor statistical theory and is too heavy for the few body problems.Therefore,a specialimportance is investigating the energy-angular distnbution of secondary neutrons of n+ ~9Be reaction.The experiment was performed with the multi-detector fast neutron TOF spectrometerat the HI-13 Tandem Accelerator at China institute of atomic energy (CIAE).Mono-energetic neutrons of 21.65 MeV were produced by the T(d,n)~4 He reaction with atritium gas target.Secondary neutron spectrum has been obtained at 25 angles in the rangebetween 15°and 145°.In the data reduction,Monte-Carlo method was employed tosimulate TOF spectra,which could be compared with the measured TOF spectra directly.The corrections for finite geometry,the flux attenuation and the multiple scattering wereincluded in the Monte-Carlo simulation.The measured DDXs were determined bycomparing the simulated TOF spectra with the measured ones with an iterative procedure.To describe the neutron induced reaction behavior of n+~9Be,a theoretical calculationbased on the Hauser-Feshbach and the exciton model for light nuclei was used.In thismodel,the pre-equilibrium emission from compound nuclei to the discrete levels of theresidual nuclei,the angular momentum dependent exciton model as well as the accuratekinematics was considered for all kinds of reaction processes.If the secondary particleemission exist,which are all from the discrete levels of the compound nuclei to the discretelevels of the residual nuclei,or through two body breakup such as ~5He~*→n+α,as well asthe three-body breakup processes of ~6He~*→n+n+α.The comparison of the measuredresult and the calculated result is presented and some analysis and discussion are addressed.Well agreement between the experimental data and the calculated results has been obtained.