Briden P E, Holt P D, Simmons J A
A.E.A. Technology, Harwell Laboratory, Didcot, Oxon, United Kingdom.
Radiat Res. 1994 Nov;140(2):230-40.
A low-pressure cloud chamber was used for several years to display the tracks created by the passage of ionizing particles through vapors of interest. The spatial distributions of the ions that were formed were of special interest, but the accuracy with which these distributions could be determined was reduced by the presence of diffusion. This meant that the droplets, when photographed, had moved significantly away from the point of creation of the parent ion. In the present investigation photographs obtained by previous workers have been analyzed in an attempt to quantify the extent to which the droplets had diffused. The results suggest that the diffusion, when converted to standard density (1000 kg/m3), was independent of the pressure inside the cloud chamber and the mixture used. It could be represented by a one-dimensional root-mean-square diffusion distance whose value was calculated to be 2.42 +/- 0.04 nm. Values for the diffusion of thermalized electrons (< approximately 4 eV) before capture to form negative ions were also calculated. They appeared to lie in the range 3.5-5.0 nm, and were again independent of the pressure and nature of the mixture. The magnitude of the diffusion was large enough to mask any measurable prediffusion structure for a distance in the region of 10 nm radially around the track path of the alpha-particle and proton tracks analyzed.
一个低压云室被使用了数年，用于展示电离粒子穿过感兴趣的蒸汽时产生的径迹。所形成离子的空间分布是特别令人感兴趣的，但由于扩散的存在，确定这些分布的准确性降低了。这意味着在拍摄时，液滴已经从母离子产生点显著移开。在本研究中，对先前研究人员获得的照片进行了分析，试图量化液滴扩散的程度。结果表明，当转换为标准密度（1000千克/立方米）时，扩散与云室内的压力和所使用的混合物无关。它可以用一维均方根扩散距离来表示，其值经计算为2.42±0.04纳米。还计算了热化电子（<约4电子伏特）在捕获形成负离子之前的扩散值。它们似乎在3.5 - 5.0纳米范围内，并且同样与压力和混合物的性质无关。对于所分析的α粒子和质子径迹，扩散的大小大到足以在径迹路径周围径向约10纳米的区域内掩盖任何可测量的预扩散结构。
