Video Transcript
Which of the following most correctly explains how radioactive materials deep in the
ground can contaminate the surface of Earth? (A) Nuclear radiation from radioactive materials forms small tunnels to the surface,
and air carries small fragments of radioactive materials from the bottom of these
tunnels to the surface. (B) Water flows through the ground and can flow from deep underground back to the
surface. The water can carry fragments of radioactive materials.
Before we answer this question, let’s first remember that radioactive contamination
occurs when unstable atoms from a radioactive object are transferred to a different
object. In this question, we are assuming that the unstable atoms are deep in the ground and
are a source of nuclear radiation. Let’s also consider that, in order to contaminate the surface of Earth, these
unstable atoms would have to travel up through the ground and reach the surface.
Now that we’ve reviewed the basics of radioactive contamination, let’s decide which
scenario is more likely to occur. Let’s say that this small green ball is below the surface of Earth and is a source of
radiation. This means it contains atoms that are emitting nuclear radiation from within their
nuclei. The nuclear radiation emitted is traveling some distance through the ground, but the
radiation does not produce tunnels.
The ground is made of soil and mineral particles, and there are gaps between these
particles. These gaps are large enough that atoms can move through them for some distance at
least. We also know that groundwater exists underground and this water can travel to the
surface. Knowing these facts, we can see that it is possible for the small green ball to
travel to the surface with groundwater. It is not possible for the small green ball to be transported by air through tunnels
made by the radiation, as no such tunnels are formed by the radiation.
And so, we can say that the correct answer is option (B). Water flows through the ground and can flow from deep underground back to the
surface. The water can carry fragments of radioactive materials.
