Video Transcript
In this video, we will learn how to
identify different sources of nuclear radiation. As we’ll see, some of these sources
are natural and some are artificial made by humans.
As far as natural sources of
radiation, believe it or not, the Earth itself is a source. Much of the Earth is made of
rock. When we take samples from the outer
layer of this rock, called the crust, we find very, very small amounts of
radioactive material. Only about 10 out of every one
million atoms in the Earth’s crust is made of such a material. The radioactive elements we might
find in the crust include thorium and uranium.
As we think about the surface of
the Earth, we know that most of it is covered by water. The water in Earth’s oceans and
seas passes through rock in the crust and picks up some radioactive material. We can say then that rock, soil,
and water are all natural sources of radiation. We can even go a bit further. Because what grows in soil and
through water is food that humans eat, even some of our food is a radiation
source. A person on Earth is exposed to all
of these natural sources. The radiation levels from these
sources is quite low. It’s not enough to be harmful to
humans.
Along with sources of radiation
from the Earth, there are also sources from space. One of these sources is the
Sun. The Sun and other active stars are
like big nuclear reactors. Nuclear radiation from the Sun
travels through space and reaches Earth. Most of this radiation is blocked
by Earth’s atmosphere. Going outside Earth’s atmosphere on
missions to space requires special protection from this radiation. Any radiation coming from outside
Earth’s atmosphere is called cosmic radiation.
We see then that natural sources of
radiation really are all around us. Shielded as we are by Earth’s
atmosphere, this background radiation is not hazardous to us. The reason for this, as we’ve seen,
is that radioactive material is so rare on Earth. We could say that we find it
everywhere but just barely. It’s possible, though, to purify
samples of rock and soil so the radioactive sources are more abundant. This gives us a highly concentrated
piece of radioactive material. Because a sample this concentrated
doesn’t naturally occur, we call it artificial.
There are two main uses for
artificial sources of radiation. One is in nuclear power plants. These plants generate electricity
from nuclear energy. A second use of artificial sources
of radiation is nuclear weapons. When a nuclear weapon detonates, it
spreads radioactive sources into the environment. Currents of air carry radioactive
material all throughout the Earth. Radioactive material is also
released onto the ground. Nuclear weapons, then, are a source
of radiation.
Nuclear power plants, on the other
hand, when they operate properly, are not a significant source of radiation. Under normal operation, the reactor
core shields the radioactive sources in the reactor so that they and the radiation
they give off is contained. However, in the case of an
accident, nuclear radiation may no longer be properly contained. In an explosion, it’s even possible
for the radioactive source to enter the environment. So a nuclear power plant can be a
source of radiation when there’s an accident. These are quite rare, but they are
possible.
A nuclear weapon, on the other
hand, is always a source of radiation whenever it’s detonated. Detonating a nuclear weapon
releases radiation and also the sources of that radiation, the radioactive materials
themselves.
Let’s look now at a few examples
about sources of radiation.
Is nuclear radiation emitted by
Earth?
Planet Earth is made largely of
rocks. When we analyze these rocks, we
find very small amounts of nuclear material. More common radioactive elements on
Earth include uranium, radium, and radon. Even though it’s in very small
amounts, too small to be dangerous to humans, nuclear radiation is emitted by the
Earth.
Let’s look now at another
question.
Does any nuclear radiation emitted
by some objects beyond Earth reach Earth?
When we think of objects beyond
Earth, that would be any object in space. Nuclear radiation is created in
stars, and that includes our Sun. Just as light from the sun reaches
Earth, so does nuclear radiation it gives off. Most radiation from space, called
cosmic radiation, is blocked by Earth’s atmosphere. Nonetheless, some does make it
through and reaches Earth’s surface. In answer to this question, then,
we can say, yes, nuclear radiation emitted by some objects beyond Earth does reach
Earth.
Let’s look now at a question about
an artificial source of radiation.
When an accident occurs at a
nuclear reactor, which of the following is the main health risk for people living
far away from the nuclear reactor? (A) Nuclear radiation escaping from
the reactor. (B) Sources of nuclear radiation
escaping from the reactor.
Our two answer options might seem
similar, but there’s an important difference between them. Say that we have a source of
nuclear radiation. This could be a chunk of
radioactive material like uranium or plutonium. This source gives off
radiation. The source and the radiation are
two separate things. In this example, we’re imagining an
accident at a nuclear reactor. So let’s say that here is our
reactor that has had an accident, say, by a hole being opened up in the reactor. We want to know what is the main
health risk for people living far away.
During normal operation, a nuclear
reactor contains radioactive material. The reactor is designed to shield
this material from spreading as well as block the radiation it gives off. If a hole was opened in the wall of
the reactor, two different things could escape: first, nuclear radiation, what is
given off by the radiation source. It’s also possible, though, that
the source of the radiation itself could be released from the reactor.
For people living far away from the
reactor, the radiation by itself escaping would not pose a significant health
risk. That’s because it has to travel
such a long distance that by the time it reached these people, it would not be very
harmful. However, if the sources of
radiation themselves were projected out of the reactor, these could then give off
radiation at a much closer distance to the people concerned. So it’s the sources escaping from
the reactor that is more dangerous than the radiation itself. We choose answer option (B).
Let’s look now at one last
example.
Which of the following correctly
describes the relation between nuclear waste and nuclear radiation? (A) Nuclear waste is a source of
nuclear radiation. (B) Nuclear waste is a type of
nuclear radiation.
So we’re trying to decide whether
nuclear waste is a source or a type of nuclear radiation. Let’s start by considering just
what nuclear waste is. A nuclear reactor is designed to
safely contain sources of nuclear radiation. When these sources become depleted,
they are removed from the reactor and put into thick containers. These depleted sources of radiation
are called nuclear waste. The reason nuclear waste needs to
be contained is it’s still a source of radiation. If nuclear waste was a type of
radiation, it would radiate out and disappear quickly. But because it is a source
constantly giving off nuclear radiation, it must be shielded from the
environment. We choose answer option (A).
Let’s now finish this lesson by
reviewing a few key points. In this video, we saw that sources
of nuclear radiation naturally exist on Earth and in space. Nuclear radiation from space is
called cosmic radiation. And lastly, we learned about
artificial sources of nuclear radiation. These include nuclear reactors that
have experienced an accident and nuclear weapons. This is a summary of sources of
radiation.
