Video Transcript
Which of the following statements
is the correct definition of background radiation? A) Background radiation is any
electrically neutral radiation. B) Background radiation is
low-level radiation from the surrounding environment, which is not due to the
deliberate introduction of radiation sources. C) Background radiation is any
low-energy electromagnetic radiation. D) Background radiation is any
radiation from sources that have a half-life of less than one minute.
Okay, so to answer this question,
let’s start by recalling that background radiation is low-level radiation that’s
present everywhere on Earth. The amount of background radiation
does vary from place to place. But in general, it’s very low
level, and for that reason it’s not really harmful to humans. It occurs mainly due to naturally
occurring radioactive substances found in the rocks beneath the earth and in the air
around us. But there are some man-made causes
to it as well.
For example, if we look at this pie
chart, which shows us the percentages of background radiation produced by different
sources, then we can see that the majority of it, 41.6% of all background radiation,
is due to radon gas found in the air. And this radon gas is naturally
occurring, but the next largest source is medical sources at 19.8%, for example,
when radioactive isotopes are used to treat cancer. But the point is that all of these
sources are not deliberate introductions of radioactive substances to the local
environment. They’re either naturally occurring
or a by-product of something man-made. And as well as this, as we
mentioned earlier, background radiation is very low-level. And that there isn’t a lot of it
and certainly not enough to cause any serious damage to humans.
So based on this description, let’s
go through the options one by one and see which option fits best. Starting with option A, which says
that background radiation is any electrically neutral radiation. Well, we know that this is not true
because background radiation can be any kind of ionizing radiation, which includes
𝛼, 𝛽, and 𝛾 radiation. Now, 𝛾 radiation is electrically
neutral because it’s an electromagnetic wave. But 𝛼 radiation and 𝛽 radiation
are not electrically neutral, and they do form some parts of background
radiation. Therefore, option A is not the
answer that we’re looking for.
Moving on to option B then. This one says that background
radiation is low-level radiation from the surrounding environment, which is not due
to the deliberate introduction of radiation sources. And this description does match
what we said earlier about background radiation. Therefore, it looks like option B
is the answer that we’re looking for.
Quickly looking at option C and D,
starting with option C. This one says that background
radiation is any low-energy electromagnetic radiation. But this is not true either,
because like we said earlier background radiation can include 𝛼, 𝛽, and 𝛾
radiation. And 𝛼 and 𝛽 radiation is not
electromagnetic radiation. In fact, an 𝛼 particle is the same
thing as the nucleus of a helium atom. And a 𝛽 particle, or at least a 𝛽
minus particle, is an electron. And both of these are not
low-energy electromagnetic radiation. And finally, even though 𝛾-rays
are electromagnetic radiation, they most certainly are not low-energy
electromagnetic radiation. In fact, they’re very high energy
electromagnetic radiation. And hence option C is not what
we’re looking for, either.
Finally, looking at option D, this
one says that background radiation is any radiation from sources that have a
half-life of less than one minute. Now, let’s recall that half-life is
the amount of time taken for the activity, the radioactivity, of a particular sample
of radioactive material to fall to half its initial value. In other words, if a substance has
a half-life of less than one minute, then it takes less than one minute for half of
that radioactive substance to have decayed away.
But then, if this were the case,
then all of the radioactive isotopes causing background radiation would decay away
very quickly and we’d have background radiation for a few minutes. But then it would disappear in a
very short time scale. And this certainly does not
happen. Background radiation is present
constantly. Therefore, the answer to our
question is that background radiation is a low-level radiation from the surrounding
environment, which is not due to the deliberate introduction of radiation sources.
