上海科技大学知识管理系统

Background: The atomic exchange effect will lead to a significant increase in the probability density of β decays below a few keV. This effect is very important for scientific experiments such as the solar axion detection that performed by low-energy electron spectroscopy measurements. However, the atomic exchange effect involves multi-electron interactions, especially for a system with 82 electrons such as lead, there are many uncertainties in the model of the atomic exchange effect. Different parameters will lead to different trends in the energy spectrum predicted by the theory, so it is urgent to carry out experimental measurements to provide parameter limits for the theory. Aim: the probability increase brought about by the atomic exchange effect is most obvious near 0 keV, and the β energy spectrum is accurately measured near this energy point, so as to provide constraints for the physical model of atomic exchange. Method: However, it is extremely difficult to measure the β energy spectrum at 0 keV due to the limitations of electronic noise and internal conversion effects. In order to solve this problem, the excited decay path of 210Pb was taken as the observation object, by measuring the total energy spectrum of β rays and cascaded γ rays, the precise measurement of the β energy spectrum near 0 keV has been completed. Results: The analysis of the β energy spectrum of 210Pb gives the following conclusions. The experimental results first verified the theory that the exchange effect causes the probability increase at the low energy end near 0 keV. At the same time, the experimental results are higher than the existing predictions of the atomic exchange effect.Conclusion: At least for Pb element, all the electron shells have played a role in improving the probability density of the low end of the β energy spectrum, instead of the previous thought that some shells play a role in improving, and some depression. This discovery will promote the theoretical calculation of the β energy spectrum of 214Pb, so it has a very positive effect on the background estimation of experiments such as XENON1T, at the same time, it also indicates that the reactor neutrinos have a higher probability density at the omnipotent end. This discovery plays an important role in the development of frontier physics.