1. Positrons are the antiparticles of electrons and have the same mass but opposite charge.
（正电子是电子的反粒子，质量相同但电荷相反。）
2. Positron emission tomography (PET) is a medical imaging technique that uses positrons to create detailed images of structures inside the body.
（正电子发射断层摄影术（PET）是一种使用正电子创建身体内结构详细图像的医学成像技术。）