Nucleation Processes in Liquid Helium

这个低温物理项目将研究液氦中电子的性质。先前的研究表明，当一个电子被引入液氦中时，它会在液体中打开一个小空腔。这个“电子气泡”的半径约为20埃。对液体施加负压使气泡增大，在临界压力下，气泡变得不稳定并爆炸。这为检测电子气泡提供了一种方便的方法。计划详细研究当气泡被光照射，电子被激发到更高的能量状态时，会发生什么。这会导致气泡的大小和形状发生突然的变化。除了超声波实验外，还将进行离子迁移率的测量。参与该项目的学生接受一系列实验技术的培训，为他们在学术界、工业界或政府的职业生涯做好准备。在液体中形成气泡是许多不同过程的结果。当含有气体的液体的压力降低时，它们就会产生：例如，当打开可乐罐时。当流体快速通过固体表面（如螺旋桨叶片）时，也会发生这种现象，这一过程有时会造成破坏，称为空化。在这个研究项目中，气泡是在液氦中产生的，液氦是一种低温流体，沸点为-268.93摄氏度。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。选择它的另一个原因是，它可以通过一种高度可控（尽管相当深奥）的过程在液氦中产生气泡。人们已经发现，当一个电子被引入液氦时，它会迫使液体中打开一个小空腔。这种不寻常的现象和高纯度的低温液氦结合在一起，为研究气泡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，将这些知识应用于实际情况，如空化。参与该项目的学生将接受一系列实验技术的培训，并为在学术界、工业界或政府的职业生涯做好充分准备。

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.