Nucleation Processes in Liquid Helium

这个低温物理项目将研究液氦中电子的性质。 以前的工作表明，当一个电子被引入液氦时，它会迫使液体中出现一个小空腔。 这个“电子泡”的半径大约为20埃。 对液体施加负压会导致气泡增长，在临界压力下，气泡变得不稳定并爆炸。 这为探测电子泡提供了一种方便的方法。 计划详细研究当气泡被光照射并且电子被激发到更高的能量状态时会发生什么。 这导致气泡的大小和形状发生突然变化。 除了超声波实验外，还将进行离子迁移率的测量。 参与该项目的学生将接受一系列实验技术的培训，为他们在工业，工业或政府部门的职业生涯做好准备。气泡在液体中的形成是许多不同过程的结果。 它们可以在含有气体的液体上的压力降低时产生：例如，当可乐罐被打开时。 当流体快速通过固体表面（如螺旋桨叶片）时，也会发生这种情况，这是一种有时会造成破坏的过程，称为空化。 在这项研究项目中，气泡是在液氦中产生的，液氦是一种沸点为-268.93 ℃的低温流体。 选择液氦的部分原因是它是超纯的，因此可以控制或消除杂质可能产生的影响。 选择它也是因为它可以通过一个高度可控的，虽然相当深奥的过程在液氦中产生气泡。 人们发现，当一个电子被引入液氦时，它会迫使液体中出现一个小空腔。 这种不寻常的现象和低温液氦的高纯度联合收割机为气泡的研究提供了一个模型系统。 目标是了解和控制气泡的产生和生长，并在可能的情况下，将知识应用于实际情况，如空化。 参与该项目的学生接受了一系列实验技术的培训，并为企业，工业或政府的职业生涯做好了充分的准备。

This low temperature physics project will study the properties of electrons in liquid helium. Previous work has shown that when an electron is introduced into liquid helium, it forces open a small cavity in the liquid. This "electron bubble" has a radius of approximately 20 Angstroms. Application of a negative pressure to the liquid causes this bubble to grow, and at a critical pressure, the bubble becomes unstable and explodes. This provides a convenient way to detect the electron bubbles. It is planned to study in detail what happens to the bubbles when they are illuminated by light and the electron is excited to a higher energy state. This causes the size and shape of the bubble to undergo a sudden change. In addition to the ultrasonic experiments, measurements of ion mobility will be performed. Students involved in this project are trained in a range of experimental techniques that prepares them for careers in academe, industry, or government.Bubbles form in liquids as a result of a number of different processes. They can be produced when the pressure on a liquid that contains gas is reduced: For example, when a cola can is opened. They also occur when a fluid passes rapidly by a solid surface, such as a propeller blade, a sometimes-damaging process known as cavitation. In this research project, bubbles are produced in liquid helium, a cryogenic fluid with a boiling point of -268.93 C. Liquid helium is chosen in part because it is ultra-pure, so effects that might arise from impurities can be controlled or eliminated. It is also chosen because it is possible to create bubbles in liquid helium via a highly controllable, though rather esoteric, process. It has been found that when an electron is introduced into liquid helium, it forces open a small cavity in the liquid. This unusual phenomenon and the high purity of cryogenic liquid helium combine to provide a model system for the study of bubbles. The goal is to understand and control bubble initiation and growth, and, where possible, apply the knowledge to practical situations such as cavitation. Students involved in this project are trained in a range of experimental techniques and are well prepared for careers in academe, industry, or government.