Radioactive Decay or Capture

Radioactive reactions deal with the chemical instability of the nucleus in an atom. 

Nuclear Reactions

Heavy (large atomic mass) elements undergo radioactive reactions in order to increase the stability of their nuclei. 

Concept: Understanding Nuclear Reactions. 

3m
Video Transcript

Hey guys! In this new video, we’re going to take a look at nuclear reactions. We’re going to say here that nuclear reactions deal with chemical processes that take place in unstable nuclei atoms. Remember your basic picture of the atom. We have spinning around the nucleus are electrons. Within our nucleus, we have our protons and our neutrons. Our protons are positively charged. Our neutrons are neutral.
Nuclear reactions deal with us somehow affecting the number of protons within our given atom. We’re going to say this normally happens with very large bulky radioactive types of elements. We're going to say here unlike normal chemical reactions where the identities of the elements stay the same, we're going to say nuclear reactions often result in elements changing into completely different elements. We're all used to stoichiometry and balanced chemical equations.
For example, we're used to seeing we have H2 gas here plus N2 gas here combine to give us NH3 gas over here. Balancing it here, we’d put a 2 here and a 3 here. But for a nuclear reaction, we’re actually affecting the number of protons within our element. Remember, your protons or your atomic number represents the identity of that element. Every element has its own unique atomic number that no other element has. But in nuclear reactions, we’re actually messing around with the number of protons which results in us creating completely new and different elements. You could start out with calcium 20 and somehow go through some process in which calcium 20, calcium 40 I mean, becomes Argon. That's the whole basis of nuclear reactions. We go from one element to a completely new element by affecting the number of protons. Affecting the number of protons has a direct impact on the identity of the element. 

In a typical stoichiometric reaction we begin with elements as reactants and end with the same elements in different forms as products. 

In a nuclear reaction the number of protons in an element are affected and so the identity of the element changes. 

The three most common types of radioactive reactions are alpha decay or capture, beta decay or capture and gamma emission. 

Concept: Types of Nuclear Reactions. 

4m
Video Transcript

We’re going to say here when it comes to nuclear reactions, we could think the British physicist Ernest Rutherford who really did a lot of experience with nuclear reactions. His contribution to nuclear chemistry was so great that they actually named element 104 after him. Element 104 is called Rutherfordium. It's kind of umbrage to all the work that he’s done in terms of this field.
Rutherford basically broke down nuclear reactions into three major types of categories. We have our alpha decay, instead of alpha decay you may hear alpha emission. We also have beta decay, which you may also hear as beta emission. Then finally, we have gamma emission. You tend to just hear it as gamma emission. You really don’t hear the term gamma decay.
What does the word decay or emit mean? That means that the radioactive particle will be a product. Remember, if you hear the word decay or emission, that means that the radioactive particle involved in all of these reactions will be a product. The opposite of decay or emitting would be the word capture. Capture would be the complete opposite. Capture would mean that the radioactive particle involved in each of these types of nuclear reactions would be a reactant.
In alpha decay, we emit an alpha particle. In beta decay, we emit a beta particle. In gamma emission, we emit a gamma particle. These particles are what cause our elements to go from one type to another type. What you have to remember is when they say decay or emission, they're saying that this alpha particle, beta particle, or gamma particle will be a product. But if you hear the term capture or even absorption, then that means that the alpha particle, the beta particle, and the gamma particle will be reactants. This has a profound difference on what exactly your products will be because you'll be emitting or decaying these particles along with a whole new element with it.
The farther into this chapter we go, we’ll learn that beyond these three, we also have positron emissions as well as electron capture. Those will come after we learned these first three major types. Just remember, in a regular chemical reaction, we start out with let’s say carbon, we end with carbon. But in the nuclear reaction, we’re emitting or capturing radioactive particles. As a result, that's going to change the identity of my element. You can start out with calcium and end up with something completely different like Argon. 

In a radioactive decay or emission reaction the radioactive particle is ejected from the nucleus and forms a product.  

In a radioactive capture or absorption reaction the radioactive particle is taken into the element and so is seen as a reactant. 

Alpha Decay

An alpha particle is comprised of 2 protons and 2 neutrons. 

Concept: Understanding Alpha Decay or Emission.

5m
Video Transcript

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.
24 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.
84210Po
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.
84210Po  24He
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.

An alpha decay or alpha emission occurs when an unstable nucleus ejects an alpha particle to create a new element. 

Concept: The Alpha Particle. 

2m
Video Transcript

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: Write balanced nuclear equations for each of the following alpha emissions.

a) Curium (Cm) – 248

b) Bismuth (Bi) – 207 

3m

Beta Decay

A beta particle has no atomic mass and is represented by an electron. 

Concept: Understanding Alpha Decay or Emission. 

2m
Video Transcript

Hey guys in this new video, we’re going to take a look at Beta Decay, now we’re going to say that Beta decay occurs when an unstable nucleus somehow emits a(n) electron. Now we’re going to say beta particle can be represented by e for the electron. Electron here we going to say is much smaller than the other 2 sub atomic particles, so the atomic mass can just be understood as 0e and here we going to say atomic number is -1 0e because the atomic number is basically the number of protons since this is an electron, we’re going to say that it’s the opposite of a proton which is 1 so an electron is -1.
Now we’re going to say here Beta decay can be represented when we emit a beta particle so for example if we had Mercury 201 and remember that 201 means its atomic mass, so let’s say we had Mercury 201 if we look on our periodic table, Mercury has an atomic number of 80. We’re going to emit a beta particle 1 0e, now remember you’re going to say your atomic masses have to be equal to each other on both sides of the arrow and your atomic numbers as well. Here the electron has no mass so the new element is going to have a mass of 201 and then here we have to be very careful here this is -1 so - 1 + what gives me 80? Well the answer would have to be 81 because 81 - 1 gives me the 80 that I had originally. So just remember that. So here would be Tl so this would be example of beta decay or a beta emission.

A beta decay or beta emission occurs when an unstable nucleus ejects a beta particle to create a new element. 

Concept: The Beta Particle. 

1m
Video Transcript

Now we’re going to say in terms of size, we know that the alpha particles are the largest radioactive particle, so we’re going to say beta particles therefore are smaller than alpha particles. Now because they’re smaller in size they’re going to be less damaging if we ingest them. So here, they’re going to have a lower ionizing power but the problem here is because they’re smaller they’re able to better penetrate into our skin. So here they’re going to have more penetrating power and so the stopping sheet of metal or large block of wood to make sure beta particle does not enter inside our bodies. 

Beta particles are smaller in size, and therefore have more penetrating power. Luckily, they are less radioactively damaging because of their lower ionizing power. 

Example: Write balanced nuclear equations for each of the following beta emissions.

a) Magnesium (Mg) – 25

b) Ruthenium (Ru) – 102 

2m
Video Transcript

So, here we have to write the balanced nuclear equations for each of the following beta emissions, again, beta decay, beta emissions means that the beta particle will be a product, if they had said beta capture or beta absorption then it would be a reacted.
Example 1: So here were starting out with Magnesium 25, 25Mg so that’s the atomic mass.
On our periodic table Magnesium has an atomic number of 12.
1225Mg  -1 0e +1325Al
It’s going to emit a beta particle, -1 0e , so our new element that’s being created would still have the same atomic mass, and then here -1 + what number gives me 12? It’d have to be 13, because 13 - 1 gives me the 12 I started out with initially. So this element would be Aluminum (Al).
Now Ruthenium (Ru) 102, were going to say if we look on our periodic table Ruthenium has an atomic number of 44.
44102Ru  -1 0e +45105Rh
Again were going to emit a beta particle so this number stays 102 and this number it would have to be 45. So goes up to Rh.
Ok, so those are the examples of beta decays or beta emissions. 

Example: Pb – 208 is formed from Th -232. How many alpha and beta decays have occurred?

  1. 6, 2
  2. 6, 6
  3. 6, 4
  4. 4, 6
  5. 8, 2
7m

Gamma Emission

A gamma particle has no atomic mass and no atomic number and is represented by the sign gamma. 

Concept: Understanding Gamma Radiation. 

3m
Video Transcript

Hey guys, in this new video, we're going to take a look at gamma emissions. Here we’re going to say gamma radiation is related to the electromagnetic spectrum. We're going to say here gamma rays have the highest energy and therefore they have the lowest or shortest wavelength and then they have the highest frequency. Remember, you have to remember from electromagnetic spectrum theory that when it comes to energy, energy and frequency are directly proportional. All that means is if one is high, the other one would be high. But when it comes to wavelength, wavelength is inversely proportional to the both of them. All that means is that wavelength is the opposite of the other two. If they're high, it’s low. If it’s high, they’re low. It’s the complete opposite of frequency and energy. Remember, wavelength is just the distance from one wave to another wave.
Where a frequency is how many waves do you get within one second. If your distance between waves across the top to them is very large, then you don't get many waves in a second. But if the wavelength is very small, if the distance between them is very small, you can cram a bunch of them in within one second. So then you would say the frequency is extremely high and the energy is high.
Gamma rays have the highest, behind cosmic rays. Cosmic rays would actually be a little bit higher than gamma rays. We usually don't hear about this in the lecture but in lecture, so strictly lecture we’re going to say gamma rays have the highest energy and therefore they have the highest frequency and therefore the lowest or shortest wavelength. If you went beyond just general chem, you would go into physics and other higher-level sciences, they’d start talking about cosmic rays which are then even higher than gamma rays. But for right now, just focus on the simple electromagnetic spectrum. Gamma rays are going to have the highest energy.

Gamma radiation is involved in the electromagnetic spectrum. Gamma rays possess the highest energy, while radio waves have lowest energy in terms of the spectrum.  

Concept: The Gamma Particle.

3m
Video Transcript

We're going to say a gamma particle can be represented by 0 over 0 and the gamma symbol is this. You're going to say because it's 0 over 0, you should realize that a gamma-ray actually does not cause any change in your atomic mass or atomic number. Because of that, we usually see it happening with alpha decay or beta decay. But what’s the whole purpose of gamma emission then?
We're going to say when it comes to gamma emission, it has to do with the absorption of energy. Here we're going to see this wavy line represents energy. This electron is in our first shell in our atom. Here in absorption, the electron is going to absorb that excess energy and become excited and use that extra energy it just absorbed to jump up to either a higher shell number or to a higher orbital number. Basically if you go from 1s to 2s. You’re going from the first shell to the second shell. That represents absorption. You could also go from the 3s to 3d. You can skip 3p altogether and just jump up straight to 3d. Both of these examples represent absorption. The first one that represents absorption when you jump from one shell to a higher shell. Then the 3s to the 3d represents you absorbing energy and jumping up from a lower orbital to a higher orbital within the same shell. Both of them begin with the number 3, so they're both within the third shell of your atom. But d-orbitals have more energy than s-orbitals.
If we saw this, we’d have 40 over 20 calcium. It undergoes a gamma emission. We’d say that that calcium has an electron that had just absorbed energy and it’s going to become excited. We put a little asterisk by it to show that it's in an excited state. That would represent a gamma emission. We're going to say that gamma particles, they have the lowest ionizing power but they have the highest penetrating power.
If you’re ever exposed to gamma emission like gamma radiation, it's basically a done deal. You're not going to survive. Gamma radiation is extremely toxic to living tissue and biological systems. Any exposure to even a smallest amount of gamma radiation would completely eviscerate all the living cells and tissues within your body. It has the lowest ionizing power but it’s still extremely dangerous.

The gamma particle does not create a new element like the other radioactive particles, but instead causes the excitation of electrons within an element. 

Gamma Particles have lowest ionizing power, but are the most dangerous because of their highest penetrating power. 

Example: Which of the following represents an element that has experienced a gamma emission?

  1. Cl: 1s22s22p63s23p5
  2. Be: 1s22s2
  3. Na: 1s22s22p63p1
  4. N: 1s22s22p3
2m

Electron Capture

Concept: Understanding Electron Capture. 

2m
Video Transcript

Hey guys, in this new video, we’re going to take a look at electron capture. The word capture, we've been talking about this. There's decay and emission versus capture. Decay and emission means that your particle will be our product. But capture means it will be a reactant. Here we're talking about an electron. Remember, an electron is really just a beta particle. When we say electron capture, we’re really saying beta capture. They're both dealing with an electron. Beta decay, the electron will be a product. But in beta capture or electron capture, it'll be a reactant.
Here we’re going to say electron capture involves the absorption of an electron which remember, we saw as this symbol, by an unstable nucleus and is represented by the following reaction. Let's think of an example. We could deal with it francium, which is the metal most to the left and the lowest down group 1A. That’s Fr. Here we’ll say we’re dealing with isotope 223. Here capturing at this electron is not going to be a product, but it's going to be a reactant. We're going to have francium-223 and francium has an atomic number of 87. We're going to absorb an electron. What effect does that going to do? That's going to be 223 plus 0 gives me 223. Then 87 minus 1 is going to give me 86. It’ would become radon, Rn. That represents the opposite of beta decay. Instead of doing beta decay or emission, we're doing beta capture AKA electron capture.

In an electron capture or electron absorption reaction our electron particle is a reactant and not a product. 

Example: Write balanced nuclear equations for each of the following elements after undergoing electron capture.

 

a) Rutherfordium (Rf) – 263

b) Nobelium (No) – 260

c) Lead (Pb) – 207

4m

Positron Emission

A positron particle is referred to as the anti-electron particle because it looks like a positively charged electron. 

Concept: Understanding Positron Emission. 

2m
Video Transcript

Hey guys! In this new video, we’re going to take a look at positron emission. Here, we're going to say positron emission occurs when an unstable nucleus emits a positron.
What's a positron? A positron is an antiparticle of the electron. Remember, the electron is represented by this. A positron is the opposite of that. It looks like an electron but instead of it having a negative sign, it'll have the opposite sign. It will be a positive electron. A positron is considered just a positive electron. I know this is weird but again, remember we're dealing with nuclear reactions. A lot of unaccustomed things that we are not used to seeing do occur. One of them is this positron. We’re going to say here, here’s our positron. Because we're talking about the word emission again, emission would mean decay which means that this positron would be a product.
Let’s think of an example. Here, Einstein has his own element named after him, Einsteinium. We’ll deal with isotope 253 of Einsteinium. Einsteinium is Es on our periodic table. It has an atomic number of 99. We're going to emit a positron and because we're emitting a positron, let’s see. Because the atomic mass is 0, the new element is still going to be 253. But because the bottom is one, what number plus 1 gives me 99? It’d have to be a 98. Here, that would just be Cf. This would be an example of a positron decay or positron emission.

A positron decay or positron emission occurs when an unstable nucleus ejects an alpha particle to create a new element. 

Example: Write balanced nuclear equations for each of the following positron emissions.

a) Uranium (U) – 235

b) Radon (Rn) – 222 

1m
Video Transcript

Based on that, let's answer these two questions. It says: Write balanced nuclear equations for each of the following positron emissions. Again, your positron will be a product. Here we're dealing with uranium 235. Uranium is U. On your periodic table, it's going to have an atomic number of 92. We emit a positron so this is going to be 235 and 91 plus 1, it gives me 92. 91 would be in Pa.
Next one is radon which is Rn. Radon has an atomic number of 86. We emit a positron so now the element is still going to be 222 and 85 plus 1 gives me 86. That's actinium. These would be two examples of our positron emission.

Example: A nuclide of Th-225 undergoes 3 alpha decays, 4 beta decays, and a gamma emission. What is the product?

a.  Radium

b.  Radon

c.   Actinium

d.  Cadmium

e.   Antimony 

3m

Radioactive Decay or Capture Additional Practice Problems

U-236 spontaneously decays to Br-87, X and three neutrons. What is element "X"?
1. Th
2. Pb
3. La
4. Ba

Watch Solution

The thorium-232 decay series begins with the emission of an alpha particle. If the daughter decays by beta emission, what is the resulting nuclide?

Watch Solution

Balance the following nuclear reaction and identify the type of radioactive decay.

 

Watch Solution

Which one of the following forms of radiation can penetrate the deepest into body tissue?

a) alpha

(b) beta

(c) gamma

(d) positron

(e) proton

Watch Solution

A nuclide of which element can balance the following nuclear reaction?

 

Watch Solution

Uranium-238 decays spontaneously by consecutive emissions into what is believed to be a different uranium isotope. What series of emissions has most likely occurred?

(a) alpha, beta, alpha

(b) alpha, beta, beta

(c) beta, beta, beta

(d) alpha, beta, gamma

(e) it is not possible for one uranium isotope to decay into another

Watch Solution

Estimate the half-life of the isotope from the graph below.

A. 1920 days

B. 1280 days

C. 960 days

D. 640 days

E. 320 days

Watch Solution

Americium-241 is used in a number of smoke detectors; as this radioisotope decays it causes particles to ionize, conduct an electric current and thereby cause the alarm to buzz. The complete decay of Am 241 involves (successively) α, α, β, α, α, β, α, α, α, β, α and β production. 

 

1. The isotope that undergoes the first β particle emission is:

a) U-233  

b) Pa-233

c) Pa-239

d) Am-241

 

 

 

2. The isotope obtained when Am-241 has completed this decay sequence is:

a) Pb-208

b) Re-205

c) Bi-209

d) Au-209

 

Watch Solution

Technetium-97 can be produced by absorption of 2H and emission of two neutrons. What is the starting nuclide?

 

a) 97Mo

b) 98Ru

c) 97Ru

d) 96Nb

e) 96Mo 

Watch Solution