Department of Physics and Astronomy, University of California, Riverside, 92521-0413, USA.
Phys Rev Lett. 2011 Nov 18;107(21):213401. doi: 10.1103/PhysRevLett.107.213401. Epub 2011 Nov 16.
Slow positrons implanted into a porous silica film may efficiently form positronium (Ps) atoms that diffuse through a network of interconnected pores. At high Ps densities, the long lifetime of ortho-positronium atoms is reduced due to Ps-Ps spin dependent interactions at a rate that implies an effective free-space scattering cross section, σ(e) = (3.4 ± 0.5) × 10(-14) cm(-2), at least 25 times larger than the theoretical value. This enhanced interaction rate may be explained if the quantum confinement of Ps results in interpore tunneling rates that depend critically on the distribution of pore sizes, so that rather than uniformly sampling the porous matrix Ps diffusion is limited to a small subset of the pores.
缓慢正电子注入多孔硅薄膜中可能会有效地形成正电子素（Ps）原子，这些原子通过相互连接的多孔网络扩散。在高 Ps 密度下，由于 Ps-Ps 自旋相关相互作用，正电子素原子的长寿命会以一定的速率降低，这意味着有效自由空间散射截面 σ(e) = (3.4 ± 0.5) × 10(-14) cm(-2)，至少比理论值大 25 倍。如果量子限制导致 Ps 中的孔间隧穿速率严重依赖于孔径分布，而不是均匀地采样多孔基质，那么 Ps 扩散就会受到限制，只能在一小部分孔中进行，那么这种增强的相互作用速率就可以得到解释。
