Effect of permanent dipole moment of molecules onpositronium thermalization in the gases

正电子原子被原子或分子散射是一个基本的过程，为散射理论提供了一个有吸引力的试验场。近年来，利用湮灭辐射的角相关（ACAR）方法结合二氧化硅气凝胶的使用，可以提取Ps与1eV以下能量范围内原子或分子相互作用的有用定性信息。在本项目中，我们观察了Ps在Ne、H_2、N_2、CH_4和C_2H_4气体中的热化过程。通过数据分析，我们确定了这些分子与Ps之间的动量传递截面为Ne的（10*7）×10^<-16>cm^2， H_2的（17*5）×10^<-16>cm^2， N_2的（26*8）×10^<-16>cm^2， Ch_4的（17*8）×10^<-16>cm^2， C_2H_4的（23*7）×10^<-16>cm^2。我们还比较了neo-C_5H_<12>的Ps热化过程比neo-C_5H_<12>的Ps热化过程慢。这说明iso-C_5H_<12>的永久偶极子对Ps热化的影响很小。

The scattering of positronium (Ps) atoms by atoms or molecules is a fundamental process that provide an attractive testing ground for scattering theories. Recently, it has become possible to extract useful qualitative information on Ps interactions with atoms or molecules in the energy range below 1eV using the angular correlation of annihilation radiation (ACAR) method combined with the use of silica aerogel.In this project, we have observed Ps thermalization process in Ne, H_2, N_2, CH_4, and C_2H_4 gases. By analyzing the data, we determined the momentum-transfer cross sections between Ps and these molecules to be (10*7)×10^<-16>cm^2 for Ne, (17*5)×10^<-16>cm^2 for H_2, (26*8)×10^<-16>cm^2 for N_2, (17*8)×10^<-16>cm^2 for Ch_4, and (23*7)×10^<-16>cm^2 for C_2H_4. We have also compared the Ps thermalization process in neo-C_5H_<12> is slower than that in neo-C_5H_<12>. This indicates that the effect of permanent dipole of iso-C_5H_<12> is small for Ps thermalization.