Electrons...
An electron is one of the fundamental particles in nature.
Fundamental means that as far as we know, an electron can not be broken
down into smaller particles. Electrons are also responsible for many of
the phenomena that we observe in everyday life. Mutual repulsion of the
electrons in atoms in the floor and those in your shoes keeps you from
sinking and disappearing into the floor! Electrons carry electrical
current and successful manipulation of these electrons allow electronic
devices to function. For example, the picture and text on the screen in
front of you is caused by electrons being accelerated and focussed onto
the inside of the screen in front of you. A phosphor absorbs
the electrons and light is produced. A television screen is a simple
and low-energy example of an electron accelerator. A typical medical
electron accelerator
Here's a picture of a Monte Carlo
simulation of typical electron beam in a color television or computer
monitor being absorbed in the phosphor screen.
Here's a picture of a Monte Carlo simulation of an electron beam of
the sort used in radiotherapy for cancer treatment.
Here's a picture of a Monte Carlo simulation of an 5 high-energy
electrons incident on 30 cm of iron.