Thickness Control.
The amount of radioactivity which passes
through a material
can be detected and used to
control the thickness of the material.
The manufacture of aluminium
foil (for cooking) is a
good example.
A radioactive source is placed above the foil
and a detector below
it.
Some of the radioactivity is absorbed by the foil
and some passes through to the
detector.
The thicker the foil, the less
radioactivity passes through it to the
detector.
The amount of radioactivity arriving at the detector
is monitored by the computer.
The thickness of the foil is controlled by
the gap between the rollers.
If the foil is too thick,
less radiation arrives at the detector.
The computer sees that the
level of radiation is too
low
and sends a signal to the rollers to make the gap
smaller.
The smaller gap makes the aluminium foil thinner
until the amount of radiation at the detector rises up to
its normal level.
If the foil is too thin,
more radiation arrives at the detector.
The computer sees that the
level of radiation is too
high
and sends a signal to the rollers to make the gap bigger.
The bigger gap makes the aluminium
foil thicker
until the amount of radiation at the detector falls back
to its normal level
The radioactive source is a b
emitter (beta emitter).
This has the right amount of penetration to be
useful
for thickness control of aluminium foil.
A b emitter with a half-life of many
years would be used so that
1. The count rate
wouldn't keep changing each
day.
2. The radioactive source would
not have to be replaced very often.
If an a emitter
(alpha emitter) was used, all of the a-particles would be
stopped by the foil and none would
reach the detector.
The computer would not be able to control the foil's
thickness.
If a g emitter
(gamma emitter) was used,
all of the g-waves would pass through the
foil and reach the detector.
The computer would not be able to tell
if the foil was too thick or too
thin.
The thickness of paper can be controlled in the same way.
Headings Radioactivity Search
Questions 
gcsescience.com Contents Index Quizzes gcsescience.com
Copyright © 2011 Dr. Colin France. All Rights Reserved.