Experimental Study On Measurement Of ^238,240Np,²⁴¹Pu Neutron-Induced Fission Cross Section By ¹⁸O+²³⁸U System Using Surrogate Method

Nuclear data plays an important role in nuclear physics research.Among them,the cross section of nuclear reaction,especially the neutron-induced fission cross section of actinides,in the basic research of nuclear physics,the application of nuclear energy,especially the new type of reactor,is also important for the miniaturization of nuclear weapons.Nowadays,the neutron-induced reaction cross sections on stable nuclides have been studied in detail both experimentally and theoretically,and the accurate cross section data can be obtained by evaluating the experimental data.However,for the half-life of only a few years or even shorter nucleus fission cross section,the amount of data is difficult to meet the application needs.This is because if the short-lived lanthanide is measured by the method of measuring the long-lived lanthanide,it will face many problems such as difficulty in target formation,high background,short measurement time,and safe experiment.The surrogate reaction method was proposed for indirectly determining the cross sections and now it is of great significance for determining the reaction cross sections of the unstable nuclides.The basic thought of the surrogate reaction method is to populate the same compound nucleus by some nuclear reaction using some stable nuclides with the nuclear reaction of the unstable nucleus,and decays through the same channel.In China,only a small number of studies have been carried out to measure the cross section of actinides nuclides by surrogate reaction method.More than ten surrogate reaction methods have been carried out in the world to measure the neutron-induced fission cross section of actinides.In view of this situation,an experimental study using the ¹⁸O+²³⁸U system as surrogate reaction was carried out.Using a light ion and ^6,7Li surrogate reaction method to measure the cross section,this system can avoid the impact of incident particle breakup and the light contaminants on the experimental results.This experiment was performed on the HI-13 Tandem Accelerator of the China Institute of Atomic Energy.In this experiment,a silicon telescope array consisting of four groups of silicon detectors to determine the transferred（projectile-like）particles was used,the corresponding target-like nucleus was determined by the measured transfer product.This target-like product is equivalent to the compound nucleus formed by neutron with the short-lived target nucleus.The fission of the target-like product is determined coincidently by using two PPAC detectors and the silicon detector array.Using the Rutherford scattering count of the front angle Monitor detector and the counting of the silicon array,the beam can be normalized to obtain the transferred differential cross section.From the experimental results,most of the pixels can clearly identify the ¹⁴C,¹⁵N and ¹⁷N products formed by the transfer reaction.Some of the pixel points with good working condition can separate of O,N and C isotopes.The transfer differential cross sections of ²³⁸U(¹⁸O,¹⁴C),(¹⁸O,¹⁷N)and(¹⁸O,¹⁵N)were calculated by using the semi-classical theoretical code Grazing and compared with the measured results.The comparison shows that the theoretical calculated results based on the sequential transfer mechanism is smaller than the measured results,and this may reveal the importance of the cluster transfer in near-Coulomb-barrier transfer of18O+²³⁸U.In near future,the transfer mechanism will be further studied and the fission cross sections if the relevant actinides will be extracted experimentally.A short-lived nucleus neutron-induced fission cross section measurement method is proposed.In this experiment,²³⁸Np with neutron energy of 0.5-4.5 MeV,²⁴⁰Np with neutron energy of 0.5-11 MeV and neutron energy are obtained.The fission excitation function of ²⁴¹Pu at 0.5-4.5 MeV.The construction of the experimental platform of this experiment will lay the groundwork for the measurement of the subsequent alternative reaction method,and the fission cross section obtained by the subsequent analysis will have important significance for improving the accuracy of the evaluation of relevant nuclear data.