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An alpha decay or alpha emission occurs when an unstable nucleus ejects an alpha particle to create a new element.
An alpha particle is comprised of 2 protons and 2 neutrons.
Concept #1: Understanding Alpha Decay or Emission.
Hey guys in this new video, we’re going to take look at Alpha Decay.
So, remember Rutherford talked about the 3 major types of decays. There’s alpha decay, beta decay and gamma emission.
Here, we have alpha decay. We’re going to say alpha decay occurs when unstable nucleus emits a particle composed of 2 protons and 2 neutrons. Now, just think about it, we say that our atomic mass equals the number of protons plus the number of neutrons. So here our atomic mass is, we lose 2 protons and 2 neutrons. So, 2 plus 2 gives me 4. Atomic Mass = number of protons + number of neutrons = 2 + 2 = 4
Your atomic mass is protons and neutrons added and your atomic number is just the number of protons. So, the number of protons loss is 2.
Atomic number = number of protons = 2
So, we’re going to say the alpha particle is represented by 4 for your atomic mass over 2 your atomic number and here we have our alpha symbol α.
Now we can also say that on our periodic table, we have an element that also has as atomic mass of 4 and an atomic number of 2. That element is Helium, 24He. So, we can say that the alpha particle can also be represented by the element Helium because Helium has the same atomic mass as an alpha particle and has the same atomic number as an alpha particle.
And remember, we’re using the term decay. So, decay means that this alpha particle will be our product.
So if you want to take a look at an example of this, we can think of for examples on your periodic table. You could have Polonium which in your periodic table is Po. Polonium, we’re going to say let’s talk about isotope 210.
Polonium (Po) – 210
Now, remember what these nuclear reactions. They can happen with different isotopes of an element. So, on your periodic table we’ll be doing different types of decays with different types of isotopes. So, don’t worry if your atomic mass on your periodic table doesn’t match my atomic mass. That’s because I am dealing with a certain isotope of that element. Remember, isotopes have the same atomic number, so they’re the same element, but they have different number of neutrons, so we have different atomic masses.
So, here Polonium 210 means the atomic mass is 210Po. If you look on your periodic table, Polonium has an atomic number, number of protons, of 84.
Now, we’re going to undergo alpha decay. Alpha decay means we’re going to spit out or emit an alpha particle. You can represent it like this 24 α or like this 24He.
Here I’ll just choose to show it as Helium. So, we’re going to emit 4 over 2 Helium.
Now, nuclear reactions are different from regular reactions, but there are some similarities. Just like you have to have a regular chemical reaction balanced, you have to have a nuclear reaction also balanced.
So, here our total atomic mass is 210. Here we have already an atomic mass of 4. So, we need to create an element that when I added to the 4 gives me back this mass of 210. So, the new element has to be 206 because 206 + 4 gives me 210. Also, your atomic numbers need to match on both sides. This atomic numbers 2, we need it to add up to 84. So, it say that the new element would have to have 82 because 82 + 2 gives me 84. And what element would that be? Well that would be lead.
So, what we’d say here is that we’d say the alpha decay of 210Polonium creates a brand new element 206Lead.
84210Po 24He + 82206Pb
The Helium were the alpha particles that just something that we emit, that’s just waste. The new element that we’re concerned with is the Lead 206. So, this represents an alpha decay, and it’s as simple as that. Make sure that your atomic masses add up on both sides. Make sure your atomic numbers add up on your both sides.
Concept #2: The Alpha Particle
Now, if you want to talk a little bit more about this alpha particle. We’re going to say: In terms of the size of radioactive particles, alpha particle is the largest.
So, it’s bigger than your beta particle, it’s bigger than your gamma particle. So, your alpha particle is the largest of them. It is the most damaging on biological cells because it has the highest ionizing power.
Which means that somehow, if you got it into your body, that it will just shred your insides. It will irradiate all of your biological cells in your body. A person who is exposed to an alpha particle internally has very low chance of survival. The good thing is, because it has the highest ionizing power, and because it’s so large, it’s extremely difficult for it to penetrate us. Penetrate our skins and get into ourselves.
So we’re going to say: They have the lowest penetrating power and can be stopped by clothing and by the air of our environment.
We’re going to say that our clothes, even the air around us provides protection against alpha particles getting into our bodies.
Now, how could you get an alpha particle inside of you? Maybe you work in a nuclear facility, where you have contaminated water or contaminated food or there was some chemical leak and it got exposed in our environment in some way and then you ingested it. But, it is extremely hard for things like this to occur. So, alpha particles are extremely damaging to our insides, but the good thing is they’re extremely hard to get into our bodies.
The alpha particle is one of the largest radioactive particles with the highest ionizing power, but lowest penetrating power.
Example #1: Write balanced nuclear equations for each of the following alpha emissions.
a) Curium (Cm) – 248
b) Bismuth (Bi) – 207
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