Let's measure some radiation! Radiation is invisible, odorless, makes no sound, and cannot be perceived by the skin. So how can we measure it?
We use the changes that take place when certain substances are exposed to radiation. Most of the effects of radiation are either (1) ionization effects by which electrons are pulled away from matter, (2) flourescent effects in certain substances, (3) and photosensitive effects, as in film exposure. In measuring radiation, the most common methods use (1) the ionization effect. In fact, the Lauritsen electroscope used in this display and the permanent cloud chamber that allows us to see the tracks of radiation particles both rely on ionization.
Permanent Wilson Cloud Chamber Courtesy of Corporation RADO
This box utilizes radiation ionization to show the particle tracks of background radiation (mainly cosmic rays). When radiation enters the box, it contacts the atoms of air components, causes their electrons to collide, absorb a positive charge, and ionize. The surrounding vaporized alcohol molecules collect on the nuclei of the ionized air and turn into tiny droplets. When enough of these collect, they become a visible cloud. Thus, the track of radiation that has entered the box becomes visible as a cloudy trail.
（The box is showed until the end of August.）