Major ideas
1. Energetic electrons accelerated through an atomic vapor can undergo inelastic scattering with the atoms in the vapor. When the electron energy matches the energy required for a quantum level transition between energy states of the atom, the inelastic scattering cross-section is large.
2. With a suitable electrode configuration, electron beams that have undergone inelastic scattering and resulting energy loss will not have enough energy to travel to a collection plate that is biased negatively with respect to the accelerating anode grid. Thus the resulting beam current will be significantly diminished.
Major equipment
1. Quartz tube containing mercury vapor and an electrode assembly for producing and accelerating electrons through a variable potential difference between a heated cathode and anode grid and a collection electrode
2. Picoammeter for measuring detected beam current, with built-in capability to sweep beam accelerating potential. The instrument is computer controlled, with automated sweep and data acquisition.
Alternatives:
3. Heating chamber (oven) including a controllable electric heater and a temperature measurement sensor.
4. (Not yet installed: a system for detecting and measuring spectra of photons emitted from excited vapor atoms.)
Data analysis
-- (Student choice)
-- (Student choice)
Here is a link to the attached document containing prelab questions.
See the documents below.
American Journal of Physics 74, 423 (2006); doi: 10.1119/1.2174033