Radiation can be a scary word for a lot of
people. But just what is radiation exactly? I mean, you probably know that it’s responsible
for such 1950s monster movies like Godzilla, but that doesn’t tell us much. Radiation in the sense that we normally mean
the word was discovered in 1896 by Henri Becquerel when he discovered that uranium could fog
a piece of film. But even that definition of radiation is incomplete. So what is radiation, exactly? Radiation is the emission of energy by a substance. There are lots of kinds of radiation. There is electromagnetic radiation and nuclear
radiation. Electromagnetic radiation encompasses such
things as radio waves, microwaves, infrared, visible light, ultraviolet light, x-rays and
gamma rays. These are all pretty familiar and aren’t
what we normally mean when we talk about radiation. I mean, microwaves can cook things and ultraviolet
light can give you a sunburn, so it’s not like electromagnetic radiation can’t be
dangerous, but it’s generally not what people mean when they talk about radiation. Actually, gamma radiation is an example of
that kind of radiation, but we’ll return to that in a bit. When people talk about radiation, they mostly
mean nuclear radiation, which is when subatomic particles are emitted from the nucleus of
atoms. I should also say that nuclear radiation is
sometimes called ionizing radiation, as it’s energetic enough to knock electrons off atoms. But I’ll call it nuclear radiation to remind
you of the radiation’s origin. And there isn’t just one kind of nuclear
radiation. There are at least four different kinds. There is alpha radiation, beta radiation,
gamma radiation and neutron radiation. Each of these types of radiation have different
characteristics. Alpha radiation is when an atomic nucleus
shoots out an alpha particle, which consists of two protons and two neutrons. If you dust off your chemical knowledge, you’ll
recall that the nucleus of a helium atom contains two protons and neutrons, so alpha radiation
is when a radioactive element shoots out a helium atom, minus the electrons. Beta radiation is caused when an atomic nucleus
shoots out an electron. We could call it electron radiation, but the
name was invented before we identified the emitted particle as an electron. It generally occurs when a neutron in an atomic
nucleus turns into a proton and electron. The proton is kept inside the nucleus and
the electron escapes. Gamma radiation is when an extremely high
energy photon escapes the nucleus. In a sense, this isn’t different much different
than a nucleus emitting ordinary light, but the much higher energy involved means that
the gamma ray can damage surrounding material. Gamma rays are often used in comic books to
give super powers to unsuspecting spectators. By the way, x-rays are similar to gamma radiation
in many ways, but less energetic. They are like gamma radiation’s younger
and less successful sibling. And then there is neutron radiation, which
is just the emission of a neutron. In a sense, this is the most dangerous type
of radiation but, as we will see, that’s a subjective statement. So, these are the different kinds of radiation
that one encounters in nuclear physics. But, as we will see, they have radically different
properties. This isn’t a radiation safety video, but
it’s important to know at least broadly what you need to do to be safe around radiation. Perhaps obviously, the easiest thing to do
is to just get far away from radiation. Just like a fire seems cooler, the further
you get from it, distance is the easiest way to reduce your exposure to radiation. However, that’s not always possible. We live in a radioactive world. Bananas are radioactive, as are Brazil nuts. Heck, you are radioactive. I made another video discussing levels of
radioactivity and, if you watched that, you’ll understand that low levels of radioactivity
are not inherently dangerous. But there are things you might encounter that
are more dangerous- things like dental x-rays for example. Now don’t worry about dental x-rays- they
give you a very low dose and are definitely worth having, but if you’re for example,
a dental hygienist, you might encounter lots of x-rays and want to protect yourself. So it’s important to know about the ways
in which you can shield yourself from various kinds of radiation. Alpha radiation consists of heavy and slowly
moving particles with a lot of electrical charge. These properties combine to make them easy
to stop. You can stop alpha particles using a single
sheet of paper. Here- I’ll show you. Here is a sample that emits alpha particles
and a Geiger counter. The paper stops the radiation. Beta radiation consists of light and fast
moving particles with electric charge. This means that they can be stopped by reasonably
thin plates of material. For instance, we see here that they can be
stopped by a thin metal plate. Gamma radiation consists of fast moving particles
with no electric charge. This means they emit no electric fields to
interact with matter. They are therefore much harder to stop. To stop gamma rays, you need a heftier chunk
of dense material like lead. This is also true for x-rays, which is why
they put a lead apron on you when you’re getting dental x-rays. Neutron radiation consists of pretty heavy
particles with no electric charge. Since they don’t interact with atomic electrons,
they can travel long distances- say hundreds or even thousands of meters in air. The way to slow them down is not so intuitive. You have to use something with a lot of hydrogen
in it, like water or plastic. The neutrons hit the protons in the hydrogen
nuclei and knock them out. This stops the neutrons and then the charged
protons are stopped quickly much like alpha particles are. By the way, given the clicking noises you
heard, you might be wondering if the technician doing the demos here was in any danger. The answer is no. The radioactive sources we used were real,
but they were weak. This diagram shows you roughly how to shield
the various kinds of radiation. It summarizes what I’ve just said. So I’ve told you about how to protect yourself
from radiation- distance and shielding. And, for shielding, I’ve told you what works
for what kinds of radiation. But what if you can’t move away or get shielding? What impact to these types of radiation have
on human tissues? This is kind of interesting. It turns out that the different types of radiation
have distinctly different consequences in terms of biological damage. In order to figure this out, scientists took
different kinds of radiation and aimed them at various kinds of tissue and saw how much
biological damage occurred. They then came up with a number that would
account for the differing amounts of damage observed. This number is called a quality factor, or
just Q. If Q is one, that means there is no adjustment. If Q is greater than one, that means that
this particular kind of radiation is biologically more dangerous than other types of radiation. So, we see here a chart that shows the Q factor
for different kinds of radiation. We see that gamma and beta radiation and x-rays
have a Q factor of 1, which means that they don’t have an enhanced damage capability. But slow neutrons have a Q of 5, which means
that for the same amount of absorbed radiation, more biological damage occurs. Fast neutrons have a Q of 10 and alpha particles
have a Q of 20, which means that they do more biological damage than other kinds of radiation. That last one is kind of weird. I mean, alpha particles are easy to stop,
but do more damage in living tissues. But, if you think about it, this makes sense. When an alpha particle stops, it stops hard,
and deposits all of its energy in one place. This means when it hits a cell, the local
damage is extensive. This is especially true if you are unlucky
enough to inhale alpha emitting radioactive dust. That’s extremely dangerous. So I hope that this video this kind of gives
you an idea of the diversity of possible kinds of radiation. I mean, there isn’t a single kind and that
means that if you want to understand radiation and how to react in a certain situation, you
really do need to become informed. However, that does take work because, in the
end, understanding radiation is like your Facebook status when you’re deciding if
you want to get back together with your ex. It’s complicated.
