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Q
What is nuclear
radiation?
A
Nuclear radiation is radioactivity that comes from the
nucleus of certain chemicals. These chemicals are called
radionuclides and are unstable. Just as a rock balanced on
the end of a pole is likely to fall and give off energy on
the way down, so radionuclides give off energy and particles
as they break down or "decay".
Q
What happens to the nuclear
radiation?
A
Radionuclides are like fires - fires burn at different
temperatures for different periods of time depending on the
type of fuel used. They all go out in the end. Radionuclides
give off radioactivity of different energies for different
periods of time and decay away completely in the end. Every
radionuclide has a certain "half-life". "Half-life" is the
time that it takes for half the radiation to go away. If the
time period is short, the radioactivity disappears quickly.
The commonest Nuclear Medicine radionuclide is called
Technetium-99m and this has a half-life of six hours. This
means that after one day, there have been four half-lives
and only 1/16th of the radioactivity is left. This makes it
very safe.
Q
How does Nuclear Medicine
compare with X-rays?
A
In Nuclear Medicine, the radiation is inside the person
shining out and is detected by the gamma camera. For an
X-ray, the radiation is shone through from the outside by a
machine and what passes through the body completely is
detected by a photographic film on the other side.
The doses of radiation from Nuclear Medicine tests are
similar to those from X-ray tests and are kept as low as
possible. For example, the radiation dose from a bone scan
is the same as for a kidney
X-ray (pyelogram).
Q
What are the types of nuclear
radiation?
A
There are three types
- alpha, beta and gamma. The alpha is a big particle and is
not found in Nuclear Medicine tests. The beta is a smaller
particle from the nucleus and is only found in radionuclides
that are used for treating diseases. The gamma is not a
particle but rather a small packet of energy. This is the
commonest form of nuclear radiation in Nuclear Medicine
tests.
OTHER QUESTIONS ABOUT RADIATION
Q
Are we normally exposed to radiation?
A
Yes, we are all exposed to
radiation every day.
This comes from :-
i.
The environment in building materials such as bricks,
mostly in the
form of radon
gas.
ii.
From inside our bodies, in naturally occurring
radionuclides particularly
potassium in
the food we eat.
iii.
From outer space in the form of cosmic radiation.
Radiation exposure
is measured in units called Sievert (Sv). Over a year,
we all get about two thousandths of a sievert of
radiation (2 mSv) from these sources. The radiation dose
from scans and X-rays ranges from 0.5 -10mSv. For
example, the dose from the bone scan is about 5mSv.
Q
Do the levels of natural
radiation vary?
A
Radiation levels are
different in different parts of the world depending on the
natural environment. In some places, there is a lot more
radiation in the soil. For example, in Kerala in India, the
sand is radioactive. Also the level of radon gas which is in
building materials, particularly bricks, varies about
100-fold, depending on where you are in the world.
The level of cosmic radiation is greater at higher
altitudes. For example, it is twice as much in Katoomba as
in Sydney. A plane trip from Sydney to London gives you 6
months' radiation in 1 day.
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