Video Transcript
In this video, we will learn how to
describe the dangers to the health of living organisms from nuclear radiation. Before we get into these effects,
let’s recall a bit about nuclear radiation.
All matter is made of atoms, and at
the center of every atom is something called the nucleus. We’ve drawn it here as a ball, but
we know the nucleus really is made up of particles called protons and neutrons. These smaller particles in the
nucleus experience forces that pull them together and also that push them apart. When the pushing and pulling forces
balance out, the nucleus is said to be stable. However, when there’s an imbalance
of forces, that unstable nucleus becomes likely to emit nuclear radiation.
Nuclear radiation can consist
either of particles or electromagnetic waves. In either case, this radiation
transmits energy; that is, it carries energy from the decaying nucleus to wherever
the radiation goes. That radiation might zoom off into
space or be absorbed by the ground. But then it might also interact
with a living organism. This means that atoms in that
organism, either on its surface or in its interior, absorb the radiation. When atoms absorb radiation, they
may well change. These changes can be passed on to
what are called cells. All living organisms are made of
cells.
We can picture cells as very small
objects, usually too small to see by eye, with an irregular shape and a central
region in the cell. This region contains what is called
the cell’s DNA. A cell’s DNA is like an ordered
list of instructions for reproducing the cell. When the atoms in a cell absorb
nuclear radiation, there are several possible effects.
Since nuclear radiation transfers
energy, it’s possible for the cell to be heated up. This may or may not be damaging to
the cell. If the cell is heated only a small
amount, it may be able to continue functioning normally. However, if there is enough
heating, the cell may indeed be damaged. Damage to a cell means it’s no
longer able to perform its normal job. When a cell’s DNA is damaged, this
means the instructions for reproducing the cell are no longer correct. At this point, a couple different
things can happen.
If the cell cannot reproduce
itself, it will die out. On the other hand, if damaged DNA
is still able to be reproduced, but perhaps incorrectly, this can lead to what is
called a mutation. That’s when a cell or even an
organism changes its form in some unintended way. Again, depending on just how the
DNA in a cell may be damaged, a mutation may be passed on from one generation to
another to another of cells. In extreme cases, mutations can
lead to a change in form of an organism. Mutations are also the cause of all
known cancers.
The energy transmitted to a cell
that may lead to these effects comes in two categories. Radiation can directly transfer
thermal energy to a cell, and indirectly, it can transfer chemical energy. So cell heating, cell damage, and
cell death may be due to a combination of thermal and chemical energy transfer due
to nuclear radiation. Now let’s say that this cell is
part of a larger organism. Say that it’s one cell in a
person’s body.
Nuclear radiation can affect an
organism in ways different than the ways it affects a single cell. If enough cells in an organism are
sufficiently heated, the organism overall may experience radiation burns. The effect of these burns is like a
sunburn, but it can occur both on the outside and inner parts of an organism. Due to the transfer of chemical
energy, an organism may also experience radiation poisoning. This can lead to symptoms including
organ failure, internal bleeding, and blindness.
So the possible effects of
radiation on an organism can be quite serious. Despite this, radiation has been
found to be quite useful in some areas of medicine. For example, X-rays are one type of
radiation, though not nuclear in origin, that help us understand the health of the
body. Since radiation can be damaging but
can also be useful for human health, the dose of this radiation in medical
applications is carefully controlled. The dose amount tells how much
radiation a person’s body absorbs. Radiation doses for people can be
measured in a unit called the rem. An X-ray on a person’s wrist, for
example, involves a dose of about 0.006 rem.
In general, the larger the dose,
the greater the chance of that radiation negatively affecting a person’s body. But besides increasing the dose,
there’s another way that nuclear radiation can be dangerous to human health. Even though the radiation dose of a
single wrist X-ray, for example, is quite small and not generally dangerous, think
of how this dose would change if the X-ray, instead of just lasting an instant of
time, was left on continuously. That is, for minutes or even hours
or days a person’s wrist was being X-rayed. Even though the amount of radiation
absorbed by the person at any one moment is quite small, by extending their exposure
time to the radiation, even that small dose can add up to have a damaging
effect.
In general, there are two ways that
radiation can be harmful or even fatal to a person. First, the person could absorb a
large dose of radiation for a short amount of time. And second, if a small dose is
applied but for a long time, that is, a long exposure time, because of the possible
danger nuclear radiation poses to humans, the amount of radiation a person is
exposed to on purpose, say, for medical reasons is carefully quantified and
limited. Knowing all this, let’s look now at
a few examples.
Which of the following correctly
describes the most severe effect on living cells that can result from them absorbing
nuclear radiation? (A) Cells dissipate energy. (B) Cells are damaged. (C) Cells are killed.
When radiation is emitted by a
nucleus, it may be absorbed by the atoms in a cell that help make up a living
organism. A cell has various parts; we
haven’t drawn them here. But the point is that practically
nuclear radiation can transfer energy to a cell. The radiation may directly transfer
thermal energy and indirectly transfer chemical energy. If a cell is heated through thermal
energy, the cell may simply dissipate that energy through cooling with no negative
effects.
So we see then that option (A)
cells dissipating energy is one result of them absorbing nuclear radiation. But it’s a very minor one. Recall we’re looking to identify
the most severe effect on a living cell. A cell may also be damaged by
absorbing nuclear radiation; for example, it may heat up enough so that the cell no
longer functions properly. It’s still possible, though, for a
damaged cell to reproduce itself. Depending on the type of cell
damage sustained, this reproduction may not be accurate, but still in this case, the
cell remains alive.
Option (C), however, describes an
outcome where a cell has absorbed enough nuclear radiation that the energy
transferred to it results in cell death. A dead cell, of course, can’t
reproduce itself. So a cell being killed is the most
severe effect on that cell that can result from an absorbing nuclear radiation.
Let’s look now at another
exercise.
Which of the following is measured
by the unit rem? (A) The radioactivity of an object,
(B) the nuclear radiation absorbed by a person, (C) the intensity of nuclear
radiation at a point.
Let’s think about these three
answer options in the context of a person being exposed to nuclear radiation. For a person to be exposed to
radiation, first, there needs to be some object, say, this one here, that emits
radiation. So let’s say this object is indeed
giving off nuclear radiation and that a person is exposed to it. While some of this radiation may
pass right through the person, some may also be absorbed. When this happens, there is a
transfer of energy to the atoms in the person’s body that absorbed the
radiation.
The unit rem is designed to
indicate just how large of a dose of radiation is absorbed. If the unit rem described the radio
activity of an object, then in our sketch we wouldn’t need to involve a person. We would just consider this part of
the diagram. But this unit does have to do with
how a person experiences, that is, absorbs, radiation. We won’t choose answer option
(A).
Considering option (C), this claims
that the unit rem has to do with the intensity of nuclear radiation at a point. Once again, this definition has
nothing to do with how much radiation a person absorbs. If option (C) was correct, we could
pick a point in space, say, this point here, and use the unit rem to indicate the
intensity of nuclear radiation at that point. However, the unit rem is used for
medical purposes. It’s designed to help safeguard
people from being overexposed to nuclear radiation.
The unit rem gives a quantitative
measure of the amount of nuclear radiation absorbed by a person. Notice that this does not include
any nuclear radiation that the person will be exposed to but that they don’t
absorb. This points to the fact that the
unit rem is designed to support human health and safety.
Let’s look now at one last
example.
A technician in a nuclear waste
storage facility receives a very small radiation dose every day that they work. Which of the following statements
correctly describes the effect this has on their health? (A) The more days the technician
works, the more harm they suffer from nuclear radiation. (B) The dose that the technician
receives is never large enough to harm them, and so their health is unaffected.
We have here a scenario where a
nuclear technician receives a very small dose of radiation every day that this
person goes to work. Because this daily dose is so
small, receiving it on any given day is unlikely to lead to a negative health
effect. But the thing is, the technician is
exposed to this very small dose day after day after day. Damage caused to the body by
nuclear radiation is cumulative. This means that every time a person
is exposed to nuclear radiation, it adds to the likelihood that they will be
harmed.
By way of analogy, consider a
person who gets a sunburn. Getting burned by the sun once is
painful but likely won’t have any negative long-term health effects. However, if a person gets a sunburn
day after day, after week, after month, after year, those small bits of daily damage
to the skin will add up. In the long term, the likelihood of
this person developing skin cancer increases.
A similar principle applies for our
nuclear technician. The more days the technician works,
the more cumulative harm they suffer from nuclear radiation. A solution, of course, is for the
technician to stop going to work. But that’s something they can work
out with their supervisor.
Let’s finish our lesson now by
summarizing a few key points. In this video, we saw that nuclear
radiation may affect cells by heating them, damaging them, or even destroying
them. We learned further that when the
DNA of a cell is damaged, this may result in a mutation. A mutation in a cell or a gene or
an organism can be passed on to later generations. This may lead to a cancer or
another abnormality in an organism. On the other hand, nuclear
radiation may affect organisms by radiation burns or radiation poisoning.
Because radiation can be harmful to
organisms while also having applications in medicine, a unit called the rem was
developed to measure the radiation dose absorbed by a person. And as a final point, nuclear
radiation can be harmful or even fatal to a person if a large dose is received over
a short time or a small dose is received continuously over a long time. This is a summary of the effects of
radiation on living organisms.
