Dipartimento di Fisica, Università di Trento and INFN, Gruppo collegato di Trento, Via Sommarive 14, I-38050 Povo, Trento, Italy.
Phys Rev Lett. 2010 Jun 18;104(24):243401. doi: 10.1103/PhysRevLett.104.243401. Epub 2010 Jun 16.
High formation yield and a meaningful cooled fraction of positronium below room temperature were obtained by implanting positrons in a silicon target in which well-controlled oxidized nanochannels (5-8 nm in diameter) perpendicular to the surface were produced. We show that by implanting positrons at 7 keV in the target held at 150 K, about 27% of positrons form positronium that escapes into the vacuum. Around 9% of the escaped positronium is cooled by collision with the walls of nanochannels and is emitted with a Maxwellian beam at 150 K. Because positronium quantum confinement limits the minimum achievable positronium energy, the tuning of the nanochannel's size is crucial for obtaining positronium gases in vacuum at very low temperature.
通过在硅靶中注入正电子，产生了垂直于表面的、直径为 5-8nm 的可控氧化纳米通道，从而获得了高产率的正电子和在室温以下有意义的冷分数正电子素。我们表明，通过在 150K 下将 7keV 的正电子注入靶中，大约 27%的正电子形成正电子素并逃逸到真空中。大约 9%的逃逸正电子素通过与纳米通道壁的碰撞而冷却，并以 150K 的麦克斯韦束发射。由于正电子素量子限制限制了可达到的最小正电子素能量，因此纳米通道尺寸的调整对于在极低温度下获得真空中的正电子素气体至关重要。
