The Nature of alpha, beta and gamma radiation
A Geiger-Muller counter can be used to detect radioactivity. When radioactive
particles enter the tube, a clicking noise is heard. The number of clicks per minute
is called the count rate. Even when there are no radioactive sources around, the
counter detects a small amount of radioactivity. This small count is due to
background radioactivity from certain building materials and cosmic radiation
from space. Radioactive materials are also in the air and in our food. The
background radiation does not cause any problems. When a source is present,
the count rate = total count – background count
The penetrating power of different radiation
Experiment: The background count is established. Different radio isotopes are used.
Each isotope has different materials and different thickness of material between it
and the detector.
Isotope Type of radiation Stopped by Penetration
The danger of different radiation
Radiation from radioactive materials ionises neutral atoms when they collide. The
ionised particles are detected by the Geiger-Muller tube. If the radiation affects
atoms and molecules in living organisms, then cells can be damaged. Large doses
of radiation can cause cancer and very large does can kill cells including cancer
cells and micro-organisms.
Outside the Damage done
body
alpha 1 Which type would you
use to sterilise
beta strawberries?
2 Which type would you
gamma use to measure the
thickness of paper?
Inside the body Damage done 3 How would you protect
workers in the nuclear
alpha industry from all types
of radioactivity?
beta 4 Why is there no danger
from irradiated food?
gamma
less dangerous - radiation less strongly absorbed
less dangerous not likely to reach living cells
more dangerous can reach cells and be absorbed
most dangerous - radiation strongly absorbed
