精确测量4He的电极化率

The electric polarizability of 4He is one of the fundamental structure parameters of the 4He nucleus. Accurate value of electric polarizability of the 4He not only can help to precisely determine the atomic energy levels of 4He, but also can help to check the NN interaction potential. Up to now, there is only one experimental result of 4He‘s electric polarizability which is indirectly extracted by the method of Compton scattering. However, the accuracy of this result is questionable. Based on HI-13 tandem accelerator in China Institute of Atomic Energy, this project intends to measure the elastic cross section of 4He nuclei on heavy targets (208Pb, 144Sm) at low energies, and to obtain the high precision (less than 0.1%) super ratio R(E) of elastic cross section. Then, using the modified Fresco code, the polarizability of 4He can be extracted by fitting the R(E) data. This project aims to measure the polarizability of 4He for the first time by the method of elastic scattering, and to accurately determine the value of the electric polarizability of 4He eventually. In addition, this project can lay a solid foundation for measuring other nucleus’s electric polarizability through the elastic scattering method. Furthermore it is helpful to further study the electromagnetic polarizability of nucleus by Compton scattering method at Shanghai Laser Electron Gamma Source (SLEGS) in the near future.

4He原子核的电极化率是其核结构的基本物理量之一。准确确定的4He原子核的电极化率可以帮助得到高精度的4He原子能级，还可以帮助检验NN相互作用势。目前，实验上只有一个用康普顿散射法间接测量的4He原子核电极化率数据，并且其精确度值得商榷。本项目拟在原子能科学研究院的HI-13串列加速器上精确测量4He与重靶（208Pb，144Sm）的低能弹性散射截面，进而得到精确的（误差小于0.1%）弹性散射截面重复比R(E)。运用加入极化势的Fresco程序对R(E)数据进行拟合提取4He的电极化率。本项目有望首次通过弹性散射法测量4He原子核的电极化率，并最终准确确定4He原子核电极化率的数值。另外，本项目将为利用弹性散射方法测量其他核的电极化率打下基础，同时也对将来利用上海激光电子伽玛源(SLEGS)通过康普顿散射对核的电磁极化率进行更深入地研究有着补充和联系的意义。