Experimental Study Of ^natEr, ^natSm And ¹⁰⁷Ag （n,γ） Cross Section

The(n,γ)cross-section has various applications in nuclear physics,nuclear astrophysics,and nuclear science and technology.Accurate cross-section data is a priority in many related works.The origin of heavy elements has always been a concern in astrophysics.The big bang is to generate light elements.The elements from carbon to iron can be well explained by the nuclear combustion process of stars.Neutron capture reaction instead of nuclear fusion is the main way to synthesize elements heavier than iron.Multiple isotopes of samarium and erbium elements are the isotopes produced using the s process,such as 166,167,168Er and 146,147,148,149,150,152Sm.Meanwhile,162,164Er and 144Sm are three of the p nuclei,and 170Er and 154Sm are produced by r-process.Their(n,γ)crosssections are of great significance for understanding celestial nuclear reactions.Because they are important input parameters for the celestial network.Nuclear energy has been paid more and more attention with the development of nuclear science and technology.Pressurized water reactors are still the main reactor type for nuclear power plant.The silver indium cadmium(Ag-In-Cd)control rod is widely used in pressurized water reactors and it is continuously consumed in a high neutron flux environment.The neutron capture cross-section of 107Ag is the calculation parameter of the macroscopic neutron cross-section of the Ag-In-Cd control rod.Therefore,it is directly related to the reactor safety design.Additionally,149Sm is a 235U fission product with a 1%yield,and it has a large neutron absorption cross-section at thermal energies.Its cross sections are thus of concern to reactor neutronics.In this work.The neutron capture yield of natEr,natSm and 107Ag,using C6D6 liquid scintillator and pulse height weighting techniques(PHWT)to measure prompt y rays,has been measured by back streaming white neutron facility(Back-n)at the China Spallation Neutron Source(CSNS).The resonance parameters were analyzed by R-Matrix SAMMY code.The resonance peaks contributed by the different isotopes are considered individually.The single-level and multi-level Breit-Wigner cross sections are calculated using experimental resonance parameters.The main conclusions are as follows:1.For natEr target.The neutron capture cross-section was measured in the energy range of 1-100 eV.The deduced neutron capture cross sections match the evaluation databases ENDF/B-Ⅷ.0,ENDF/B-Ⅶ.1,JENDL-4.0,and ROSFOND-2010,and resonance parameters extracted from the R-matrix code in the 1-100 eV region.Experimental results show the contribution of 170Er widely off at 95 eV.162Er has a resonance structure at 51.4 and 67.8 eV,but there is no clear resonance peak in the experimental data.These need further independent measurements for check.2.For 107Ag target.The(n,γ)cross-section was measured in the energy range of 160 eV.The resonance parameters were extracted using an R-matrix code.Experimental results show that at 41.6 eV,the experimental data were significantly lower than the evaluation values from ENDF/B-Ⅷ.0.3.For natSm target.The resonance parameters between 1 and 50 eV were analyzed by SAMMY code.The results of the capture yield indicated signs of the possibility of two resonance peaks at 8 eV,which awaits further experimental examination.Crosssection was calculated according to resonance parameters and was compared with other experimental results and evaluation databases of ENDF/B-Ⅷ.0 and CENDL-3.2.A clear difference between ENDF/B Ⅷ.0 and CENDL-3.2 databases appears at 23.2 eV,the experimental result at this energy is smaller than data of ENDF/B Ⅷ.0 database but CENDL-3.2 database.Most of the controversial experimental results invariably come from the samarium 149 isotope.The experiments involved in this work,as early stage experiments at Back-n beamline,develop and improve the basic route for the experimental study of the neutron capture cross-section at the Back-n facility.The sources of error and evaluation methods of the experiments were identified,and the background composition and time structure were also analyzed.This work provides important processing methods and parameters for future experimental works.In-beam γ-ray background is a bottleneck for data analysis.The time structure of the in-beam γ-ray background of Back-n beamlines under different experimental conditions was also studied and they are shown to be controllable.A general method for quantifying the γ-ray background in the Back-n beamline is proposed and tested.The uncertainty of the method was analyzed.This method can be applied not only to past data but also to guide future experiments.Back-n beamline is the first high-performance white neutron source in China.This work reveals neutron capture cross-section measurement at Back-n beamline.