Australian Science Illustrated — Issue 54 2017

Tiny Particles Collide

with Vapour Molecules

They are tinier than the tiniest of atoms, but they can change the world.
Fill a box with cold vapour and see the tiny particles with your own eyes.

Y

ou are constantly bombarded
with trillions of particles, but you
cannot see them, as they are tinier
than an atom. Some of the particles,
such as muons and positrons, are pro-
duced when high-energy radiation
from space collides with atoms in
Earth’s upper atmosphere. Others,
such as alpha particles, appear as
radioactive substances decay.
In the world’s leading particle phys-
ics lab, CERN, scientists use vapour-
filled chambers to detect the invisible
particles. And you can do the same
thing (with a little less detail but a LOT
less electricity) in your own home.
Isopropanol evaporates at room
temperature, and felt soaked in the

stuff can quickly fill a closed chamber

with the vapour. Cool the base with dry

ice, and the air will be so saturated with

vapour that it only takes slight external

influence to make the vapour condense

into small, visible droplets.

When the invisible particles pass

through the chamber, they use their

high energy to force electrons out of air

molecules. The air becomes positively

charged, and this charge attracts iso-

propanol molecules, which unite to

form droplets. The invisible particles

produce clear traces of small droplets,

which you can see with the naked eye.

And you can even tell which type of

particle you see based on the shapes

and sizes of the traces.

PARTICLE GUIDE

Very light particles such as electrons and

positrons change direction when they collide

with air molecules, so their traces zigzag.

The slightly heavier muons do not give way,

leaving long, straight traces. Alpha particles

are heavier, but less high-energy, so they

leave short, thick traces. Some particles

decay, and so, their traces branch out.

Every few seconds, tiny

particles pass through the

vapour at the bottom of the

chamber, leaving clear traces.

MUON

ALPHA PARTICLE

ELECTRON OR

POSITRON

PARTICLE DECAY

By Kristian Filrup