Positronium emission and cooling in reflection and transmission from thin meso-structured silica films
Positronium emission and cooling in reflection and transmission from thin meso-structured silica films
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DOI：
10.1088/0953-4075/48/20/204003
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发表时间：
2015-09
期刊：
影响因子：
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通讯作者：
S. Andersen;D. Cassidy;J. Chevallier;B. Cooper;A. Deller;T. Wall;U. Uggerhøj
中科院分区：
文献类型：
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作者：
S. Andersen;D. Cassidy;J. Chevallier;B. Cooper;A. Deller;T. Wall;U. Uggerhøj
利用单次激发正电子湮没寿命谱和多普勒谱测量了介观结构二氧化硅靶的正电子素（Ps）能量和形成分数。二氧化硅样品是使用掠射角沉积蒸发的二氧化硅悬浮在薄碳箔。通过二氧化硅样品的光学访问有利于纵向Ps能量的测量，并且发现反射几何结构中的Ps能量如预期的那样随着正电子能量而减小，横向和纵向方向的最小可实现Ps能量分别为0.203（12）和0.26（3）eV。在透射几何结构中，Ps的冷却在正电子穿透碳箔并进入介观结构二氧化硅所需的最小正电子撞击能量处变得明显。该几何形状的最小能量在横向和纵向方向上分别为0.210（12）和0.287（14）eV，并且发现可实现的最小Ps能量受到结构化二氧化硅靶的厚度的限制，因为在两种几何形状中发现相同的能量。
Measurements of the positronium (Ps) energy and formation fraction in reflection and transmission from a thin meso-structured silica target have been conducted using single-shot positron annihilation lifetime spectroscopy and Doppler spectroscopy. The silica sample is made using glancing angle deposition of vaporized SiO2 on a suspended thin carbon foil. Optical access through the silica sample facilitates measurement of the longitudinal Ps energy, and the Ps energy in the reflection geometry is found to decrease with positron energy as expected, with a minimum achievable Ps energy of 0.203(12) and 0.26(3) eV for the transverse and longitudinal directions, respectively. In the transmission geometry cooling of Ps becomes evident at the minimum positron impact energy required for the positrons to penetrate the carbon foil and enter the meso-structured silica. The minimum energies for this geometry are 0.210(12) and 0.287(14) eV in the transverse and longitudinal directions, respectively, and the minimum achievable Ps energy is found to be limited by the thickness of the structured silica target, since the same energy was found in both geometries.