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- [Voiceover] Let's look at three types

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of radioactive decay,

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and we'll start with alpha decay.

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In alpha decay, an alpha particle

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is ejected from an unstable nucleus,

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so here's our unstable
nucleus, uranium-238.

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An alpha particle has the same

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composition as a helium nucleus.

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We saw the helium nucleus
in the previous video.

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There are two protons

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in the helium nucleus and two neutrons.

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So I go ahead and draw
in my two neutrons here.

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Since there are two protons,

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the charge of an alpha
particle is two plus.

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So for representing an
alpha particle in our

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nuclear equation, since an alpha particle

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has the same composition
as a helium nucleus,

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we put an He in here,

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and it has two positive charges,

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so we put a two down here,

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and then a total of four nucleons,

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so we put a four here.

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Trying to figure out the other product

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from our nuclear equation,

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I know nucleons are conserved,

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so if I have 238 nucleons on the left,

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I need 238 nucleons on the right.

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Well, I have four from my alpha particle,

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so I need 234 more.

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So 234 plus four gives me a
total of 238 on the right,

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and so therefore nucleons
are conserved here.

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In terms of charge, I know
charge is also conserved.

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On the left, I know I have 92 protons,

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so 92 positive charges on the left.

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I need 92 positive charges on the right.

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We already have two positive charges

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from our alpha particle,

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and so we need 90 more.

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So we need 90 positive charges.

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We need an atomic number here of 90.

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The identity of the other product,

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just look it up here at our table,

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find atomic number of 90,

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and you'll see that's thorium here.

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So thorium-234 is our other product.

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So we think about what's
happening visually,

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we're starting off with a uranium nucleus

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which is unstable, it's going
to eject an alpha particle,

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so an alpha particle is
ejected from this nucleus,

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so we're losing this alpha particle,

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and what's left behind
is this thorium nucleus.

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So this is just a visual representation

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of what's going on here,
in our nuclear equation.

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Let's do beta decay.

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So in beta decay, an electron
is ejected from the nucleus.

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We saw in the previous video that

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you represent an electron,

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since it has a negative one charge,

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you put a negative one down here,

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it's not a proton, nor is it a neutron,

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so we put a zero here.

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So here's our electron and an electron

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ejected from the nucleus
is called a beta particle.

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We could put a beta here,
and it's an electron,

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so a negative one charge,
and then a zero here.

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If a beta particle is
ejected from the nucleus

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of a thorium-234, so we're
starting with thorium-234,

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this nucleus ejects a beta particle,

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so we go ahead and put
a beta particle in here,

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so zero and negative one,
what else is produced here?

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What else do we make?

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Well, once again, the number of nucleons

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is conserved, so I have
234 nucleons on the left,

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I need 234 on the right.

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I have a zero here, so
I need 234 nucleons.

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Charge is also conserved,
so I have 90 positive

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charges on the left, I have 90 protons.

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On the right, I have a
negative charge here,

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so I have a negative one charge,

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and so I must need 91 positive charges,

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because 91 positive charges

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and one negative charge gives me

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90 positive charges on the right.

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So I need an atomic number of 91.

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If you look at the periodic table,

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and you find the atomic number of 91,

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you'll see that this is protactinium.

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So we're going to make
protactinium here, so Pa.

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What is happening in beta decay?

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Let's look at it in a
little bit more detail.

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We already talked about
the number of protons,

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so we have 90 protons on the left,

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how many neutrons do we have?

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Well, 234 minus 90, 234 minus 90

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gives us the number of neutrons.

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That's 144 neutrons.

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On the right, we have 91 protons,

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how many neutrons do we have?

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Well, that'd be 234 minus 91.

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So 234 minus 91 gives us 143 neutrons.

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So we went from 144 neutrons on the left

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to 143 neutrons on the right,

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and we went from 90 protons on the left,

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to 91 protons on the right.

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So we lost a neutron,
and we gained a proton.

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You could think about the
neutron turning into a proton,

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and this is an oversimplified
way of thinking about it.

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Let's go ahead and write that down here.

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So a neutron turning into a proton.

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So a neutron has no charge,
so we put a zero here.

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And a neutron is a nucleon,
so we put a one right here.

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So a neutron is turning into a proton,

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so let's go ahead and
write our proton here.

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A proton has a plus one charge,

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and it's a nucleon so we put a one here.

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When we think about what else is made,

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we know that nucleons are conserved,

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so we have one nucleon on the left,

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one nucleon on the right.

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Therefore, we would have a zero here.

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In terms of charge, if we
have zero charge on the left,

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plus one on the right, we
need negative one right here.

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This of course represents the electron,

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so this is the electron that's
ejected from the nucleus.

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This is our beta particle.

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And also actually,
something else is produced.

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You're also going to
make an anti-neutrino,

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and that's just really
not part of this video,

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so we'll just ignore it for now.

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So a neutron has turned into a proton,

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and we're also getting a beta particle

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ejected from the nucleus.

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When this conversion, this process

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is actually governed by the weak force,

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the weak interaction, so there's a lot

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of stuff going on in the nucleus

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which we just won't
get into in this video.

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The important thing is to be able to look

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at a nuclear equation, recognize it

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as beta decay, and be able to write

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everything in your nuclear equation.

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Let's do one more type of decay.

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This is gamma decay.

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Gamma rays are given off,

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and a gamma ray has no charge and no mass;

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it's pretty much just energy,
if you think about it.

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These are pretty easy decay problems.

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Let's start with technetium-99m,

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and the m right here
stands for metastable,

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which means a nucleus
in its excited state,

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so a nucleus in its excited state,

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so it has more energy.

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It's going to give off a gamma ray,

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so let's go ahead and draw in our

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gamma ray here, so zero and zero.

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Since we're dealing with zeroes,

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so these zeroes aren't
going to affect our numbers,

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so if we start with nucleons,

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we have 99 nucleons on the left,

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we're going to have 99
nucleons on the right.

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And in terms of charges,

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we have 43 positive charges on the left,

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we need 43 positive charges on the right.

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And since the atomic
number isn't changing,

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it's 43 on the left, it's 43 on the right,

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we're dealing with technetium here.

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It's still technetium; it's
just in the ground stage.

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It's no longer in the excited state.

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It's in the ground state.

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It's given off energy in the form

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of gamma rays in this example here.

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So technetium-99m is actually used

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in several medical imaging
and diagnostic procedures,

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because we have ways of
measuring the gamma radiation,

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and so this is very useful in medicine.