The Application And Exploration Of The D-D Neutron Activation In Ar-Ar Isotope Dating

Isotopic age determination is the process of studying and determining the age of rocks,fossils,and minerals using the fundamental law of radioactive disintegration,during the crystallization and re-crystallization process.It is related to the decay of radioisotopes.Accurate determination of the isotopic age is of great significance for studying the formation history and evolution of the Earth and planets.It plays a very important role in geological research,resource exploration,ore biological evolution,climate change laws,and environmental transformation laws.Ar-Ar isotope dating is one of the most widely used dating methods in geology.It is widely used in archaeology,tectonic movement,volcanic disasters,environment and climate evolution to determine the age of various potassium-bearing mineral rocks.The measurable age ranges from the Earth's age about 4.6 billion years,down to A.D.79,the eruption of Vesuvius.Ar-Ar isotope dating method requires the conversion of ³⁹K in the sample to ³⁹Ar by neutron irradiation,when a nuclear reaction of ³⁹K?n,p?³⁹Ar occurs.Traditionally,a fission reactor is used as a neutron source to irradiate the samples.However,the expensive cost of building a reactor impose restrictions on the studying and application of Ar-Ar isotope dating.The ³⁹K?n,p?³⁹Ar activation cross section in Ar-Ar isotope dating is increased significantly between neutron energies of 1.5 Mev and 3 MeV.In this study,the author used2.5 MeV quasi monoenergetic neutrons to irradiate Ar-Ar dating samples and accurately monitor them with nickel sheets to achieve standard-free dating.After stepwise heating,cooling,gas purification,gas extraction and other processes,the author used rare gas isotope mass spectrometer with a high resolution ratio to measure the Ar isotope content,calculate and analyze the experimental results,and discuss the feasible for Ar-Ar isotope dating by using D-D intense neutron generator.At the same time,the activation cross section of ³⁹K?n,p?³⁹Ar reaction was calculated by fast neutron activation analysis and Ar isotope content measured by mass spectrometer.The result was compared with the existing experimental data and ENDF/B-VIII.0 and JEFF-3.3 evaluation data,as well as the data of TALYS 1.9.In this study,the D-D fast neutron was obtained by the CPNG-600 high-current neutron generator of the Chinese Academy of Atomic Energy.Neutron flux density is controlled by ⁵⁸Ni?n,p?⁵⁸Co,which is simultaneously irradiated with the sample,through the low-resolution high-resolution HPGe gamma spectrometer measurements'providing.And K-containing samples were provided by the Institute of Geology and Geophysics of the Chinese Academy of Sciences.At the same time,the generation nuclei ³⁹Ar and ⁴⁰Ar were measured by using a multi-obtained Noblesse rare gas mass spectrometer.In this thesis,the age of the sample is calculated by rare gas mass spectrometer through D-D neutron activation technique,and the standard-free Ar-Ar isotope dating is achieved.Compared with the standard sample age,the experimental result is close to the standard age.Finally,this thesis summarized the application and practice of D-D neutron activation technique in Ar-Ar isotope dating,which lays a foundation for expanding the application of high-tech neutron generators in geoscience,and will open up new avenues for Ar-Ar isotope dating.It also provides a strong support for the development of isotope dating technology.