Category: ATOMS AND RADIOACTIVITY

For his second crucial experiment, Thomson reattempted to deflect the cathode rays, much like Hertz had unsuccessfully tried before, but this time pulling a deeper vacuum in the tube. As shown in Figure 46, the cathode rays in his tube were made to pass between two parallel aluminum plates. Contrary to Hertz’s experience, the cathode rays…

Hertz’ (mistaken) finding that cathode rays were not deflected by an electric field was a true mystery, given that cathode rays were so easily bent by magnetic fields. In 1895, French physicist, and later Nobel Prize laureate, Jean Perrin built a CRT to investigate whether or not cathode rays transported charge.10 A diagram of Perrin’s original…

In 1879, Crookes had reached the conclusion that cathode rays must be particles of some sort, observing that they traveled in straight lines and were stopped by metallic objects in their path. As a demonstration, Crookes inserted an electrode shaped like a Maltese cross in the tube, and it cast a sharp shadow on the…

Some of the most important experiments to explain radiation were conducted in 1897 by British physicist J. J. Thomson. These experiments led Thomson to the discovery of the electron, for which he received the 1906 Nobel Prize in Physics. The story starts in 1857, when German physicist and glassblower Heinrich Geissler pumped the air out…

Our CRTs require a beam of electrons, which we produce using the assembly shown in Figure 41. Electrons are stripped off the cathode by a process known as glow discharge between an aluminum cathode rod and a hollow anode. The electron gun is built inside an Ace-Thred #11 connector (Ace catalog number 7644-10). The cathode is a 3/8-in. aluminum…

Electron beams in a good vacuum are invisible, but a screen coated with a material that fluoresces when hit by electrons can be used to make the beam visible. These fluorescent materials are called phosphors, and are used most commonly in cathode-ray oscilloscope and TV screens to produce an image by steering an electron beam inside…

Making vacuum tubes from scratch is almost a lost art. It involves plenty of practice in technical glassblowing, as well as an understanding of materials and vacuum techniques. However, vacuum tubes that operate at relatively high pressures and require continuous pumping are easy to build by cobbling together glass tubes, copper piping, and rubber corks.…

Simple mechanical pressure gauges don’t usually work at pressures below 10 Torr, so we need a different way of measuring pressure in our vacuum systems. We use the most inexpensive pressure sensor that works at these levels, which is the T/C gauge. It operates by measuring the thermal conductivity of the gas inside the chamber. As…

We will conduct our experiments in the range of 10 Torr to 10 mTorr, which is easy to achieve using a low-cost, mechanical vacuum pump. Very good results have been obtained by amateur experimenters and educators using vacuum pumps made for servicing air conditioning and refrigeration units. These vacuum pumps are not part of the…

The experiments in this chapter will deal with the production and detection of subatomic particles, such as electrons and nuclei. As these interact with matter, including air, many of the experiments need to be carried out inside glass tubes out of which the air has been pumped. The normal atmospheric pressure at sea level is…