Video Transcript
In this video, we’re talking about
gamma radiation. As this image suggests, gamma
radiation is a form of nuclear decay. When an atomic nucleus is excited
and needs to decay to a stabler, lower-energy state, one way it can do this is by
giving off gamma radiation. Now, as a bit of background, we
know that when an atomic nucleus becomes unstable, it’s a strong candidate for
experiencing radioactive decay. When this decay takes place, the
nucleus emits something. It gives something off. This something could be an alpha
particle, two protons and two neutrons. Or, it could be a beta particle, an
electron. It could be a single neutron. And it could also be what’s called
a gamma ray or gamma radiation.
Each one of these different types
of atomic emission has the same goal: to stabilize an unstable nucleus. And yet, each radiation type has
its own unique characteristics. When it comes to gamma radiation,
what makes this different is that there’s no mass involved. Gamma radiation is purely
energy. In other words, in a gamma ray,
there are no protons, neutrons, or electrons. Instead, a gamma ray, which is
often symbolized using a squiggly line like this, is what’s called a photon, a
packet of electromagnetic radiation. This symbol that we’ve drawn here
that represents gamma radiation is simply the Greek letter 𝛾. Because gamma radiation has no mass
and is purely energy, that means it has no protons or electrons, which also means it
has no electric charge.
So, let’s say that we were looking
at a nuclear equation involving gamma decay. Imagine we had a barium-137
isotope, and that this nucleus experienced radioactive decay through gamma
radiation. As we saw, the symbol for gamma
radiation is the Greek letter 𝛾. And when we write this in a nuclear
equation, it has no atomic number or mass number. The reason for that, as we saw
earlier, is that gamma radiation has no mass and no electric charge. This means we could represent a
gamma ray with an atomic number and mass number of zero, if we wanted to. Now, we know that, in general, when
it comes to nuclear equations, we need to have the same total atomic number and same
total mass number on either side.
In this case, we have a mass number
of 137 and an atomic number of 56 on the left, which means we must have those same
numbers on the right. And that gives us a clue as to what
else needs to go on the right side of this equation. It’s another barium-137
nucleus. This equation may seem confusing
because we’re starting with a barium-137 nucleus, and then we’re ending with a
barium-137 nucleus plus a gamma ray. It seems like we’re getting
something for nothing. What’s really taking place, though,
is we’re taking an excited barium-137 nucleus, and then it’s decaying into
lower-energy, stabler barium-137 plus this high-energy gamma ray.
We could say that we’re stripping
energy away from this nucleus, and we’re sending it away, so to speak, as gamma
radiation. And then, what’s left over is a
stabler version of that same isotope. So, as we can see from this
equation, gamma radiation does not lead to a change in atomic number. And it also doesn’t lead to a
change in mass number. Those two values remain the
same. And we can see that the relative
charge of the nucleus giving off the gamma ray also remains the same. This just emphasizes the point that
gamma radiation is nothing but energy. Indeed, it’s the most energetic
type of electromagnetic radiation.
Let’s consider a second example of
a nuclear equation involving gamma radiation. This time, we’ll start with
cobalt-60. When this isotope goes through
gamma decay, it gives off a gamma ray, a photon. And what’s left over is a stabler,
lower-energy version of the same isotope. Once again, we see that gamma
radiation does not change atomic number or mass number. And we also see, in this example,
that those two values, atomic number and mass number, are still balanced on the
left- and right-hand sides of this equation. Now that we know a bit about gamma
radiation and how to include it in nuclear equations, let’s get some practice with
these ideas through an example exercise.
When an atomic nucleus emits a
gamma ray, by how much does the atomic number of the nucleus change?
Okay, so in this example, we have
an atomic nucleus. Let’s say that this is it. And we’re told this nucleus emits a
gamma ray. And we can symbolize that this
way. When a nucleus emits a gamma ray,
we say that it’s giving off gamma radiation. Now, an important thing to realize
about gamma radiation is that it’s purely energy. There’s no mass involved. Another way to describe a gamma ray
is as a packet of electromagnetic radiation called a photon. Now, if a gamma ray has no mass,
that also means it has no protons or electrons in it because those objects have a
mass. So, our massless gamma ray also has
no electric charge. And this fact helps us answer our
question of how much the atomic number of this nucleus that gives off the gamma ray
changes.
The atomic number — we can call it
𝑧 — of an element is equal to the number of protons in the nucleus. Since the relative charge of a
single proton is plus one, the number of protons in a nucleus and its overall
relative charge are the same. Just as a side note, when it comes
to other subatomic masses such as beta particles, which are electrons, this
similarity between proton number and relative charge means that, often, an emitted
electron is symbolized as having an atomic number of negative one. This doesn’t mean that a beta
particle has negative-one protons, but rather that its relative charge is negative
one.
All this to say that when we’re
talking about atomic nuclei, atomic number corresponds to the relative charge of the
nucleus. And as we saw earlier, the relative
charge of a gamma ray is zero because there’s no charge or mass involved in this
radiation. That means it has no effect on the
atomic number of the nucleus from which it was emitted. So, when we talk about how much the
atomic number of that nucleus changes, the answer is simply that it doesn’t change
at all. The change is zero. Another way to say this is that the
atomic number of a nucleus that emits a gamma ray stays the same.
Let’s look now at a second example
exercise.
The following nuclear equation
shows gamma radiation by radon. What is the name of element X? What element symbol should replace
X?
All right, taking a look at this
nuclear equation, we see that we’re starting out with this element, which we’re told
is radon. The atomic number of radon is
86. It has 86 protons in its nuclear
core. And its mass number, the sum of the
number of protons and the number of neutrons in its nucleus, is 222. So then, we can refer to this
isotope of radon as radon-222. This radon nucleus experiences
nuclear decay, and it emits a gamma ray. This is the Greek symbol for that
letter 𝛾 representing this radiation. Once the gamma ray is emitted from
the radon nucleus, there’s this leftover element, element X.
Starting off, we want to solve for
the name of this element. And then, we want to know what
element symbol should replace X. These two questions are closely
connected, and there are a couple of different ways to answer them. One way is to consider that what’s
being emitted here is gamma radiation. And we can recall that a gamma ray,
a photon, a packet of electromagnetic energy, has no mass to it. And it also has no electric
charge. This means that when we consider
gamma radiation as a part of an overall nuclear equation, whatever is left over
after the gamma ray is emitted — in our case, it’s this element X — will have the
same mass and the same electric charge as what emitted the gamma ray in the first
place. In other words, this element here
and this element here are the same.
Now, there’s a second way to see
this. And that is by looking at the
atomic number and the mass number of this unknown element. When we compare these values to the
equivalent values on the left-hand side of our nuclear equation, we see that they’re
the same. Both our radon nucleus and our
nucleus of element X have an atomic number of 86 and a mass number of 222. This is a second way of seeing that
these two elements must be the same. And therefore, the name of element
X is the name of this element. Element X is radon. The next question is related. It says, what element symbol should
replace X? Well, if X is radon and the
element’s symbol for radon is capital Rn, then that tells us that that same symbol
should go in place of capital X.
Let’s look now at one last
example.
What type of particle is a gamma
ray the same as?
Okay, so thinking about gamma rays,
we know that these are emitted in radioactive emission events. The symbol for a gamma ray is the
Greek letter 𝛾. And sometimes, we’ll see these rays
represented by a squiggly line that looks something like this. And this representation can remind
us that a gamma ray is electromagnetic radiation. That is, in some respects, it
behaves like a wave. But in this question, we’re asked
specifically what type of particle a gamma ray is the same as. We can start off by realizing what
type of particles a gamma ray is not. A gamma ray, as electromagnetic
radiation, has no mass, and it also has no electric charge. That means a gamma ray can’t be any
particle that has mass or charge. It can’t be a proton. It can’t be a neutron. It can’t be an electron and so
on.
But then, what particle is there
that’s both massless and chargeless? We can think back to the identity
of a gamma ray as electromagnetic radiation. The name for a packet or a single
section of electromagnetic radiation is photon. A photon is considered to be a
particle, and yet it satisfies the condition of having no mass and no charge. Therefore, it’s a match for a gamma
ray. And therefore, this is our
answer. A photon is the particle that a
gamma ray is the same as.
Let’s now summarize what we’ve
learned about gamma radiation. In this lesson, we saw that when
radioactive nuclei decay, that is, seek out a lower-energy, more stable state, then
they may emit gamma radiation. Gamma radiation is comprised of
gamma rays, which are massless, chargeless particles of electromagnetic energy
called photons. Finally, we saw that when a nucleus
emits a gamma ray, its atomic number, mass number, and relative charge do not
change. In other words, it’s the same
nucleus as before, just in a lower-energy state. This is a summary of gamma
radiation.
