Positron Emission - Online Tutor, Practice Problems & Exam Prep

Positron emission occurs when an unstable nucleus emits a positron, which is the antiparticle of the electron, possessing a positive charge. This process is a type of nuclear decay, resulting in a new element. For example, when the isotope 253 of einsteinium (atomic number 99) emits a positron, it transforms into californium (atomic number 98) while maintaining the same atomic mass of 253. Understanding positron emission is crucial in nuclear chemistry and radioactivity, highlighting the unique behaviors of subatomic particles.

Positron Emission Concept 1

Hey guys, in this new video, we're going to take a look at positron emission. So, here we're going to say positron emission occurs when an unstable nucleus emits a positron. Now, what's a positron? A positron is an anti-particle of the electron. Remember, the electron is represented by this. A positron is the opposite of that. So, it looks like an electron, but instead of it having a negative sign, it will have the opposite sign. So, it will be a positive electron. So, a positron is considered just a positive electron. I know this is weird, but again remember, we're dealing with nuclear reactions. So, a lot of unaccustomed things that we are not used to seeing do occur. And one of them is this positron emission. So, we're going to say here, here's our positron. Now, because we're talking about the word emission again, emission would mean decay, which means that this positron would be a product. So, let's think of an example. Here, Einstein has its own element named after him, Einsteinium. So, Einsteinium will deal with isotope 253 of einsteinium. So einsteinium is Es on our periodic table. It has an atomic number of 99. Here is the equation for the positron emission we discussed:

Es 253 99 → Es 253 98 + e +

This would be an example of a positron decay or positron emission.

Positron Emission Example 1

Now, based on that, let's answer these two questions. It says, write balanced nuclear equations for each of the following positron emissions. So again, your positron will be a product. So 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:

U 235 92 → Pa 231 91 + e +

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 +1 gives me the 86. So, that's Actinium. So, these would be two examples of our positron emission:

Rn 222 86 → Ac 222 85 + e +

Positron Emission Example 2

Now, following what we've learned so far about all the different types of decays and emissions out there, let's try our best to answer this one. So here we're going to say a nuclei of thorium, oh not thallium, Thorium-225 undergoes 3 alpha decays, 4 beta decays, and a gamma emission. What is the product? So, remember Thorium has an atomic number of 90. It's going to undergo 3 alpha decays, and alpha decays basically produce the helium or alpha particle, plus 4 beta decays, so that's 4 electrons being emitted, plus gamma, which is 0 over 0. So, basically when you have 3 helium particles being emitted, that's 3×4 which is 12, 3×2 which is 6, 4×0 which is 0, 4× -1 which is -4. Again, this is not the proper way to write it. I'm just combining all the math just to make it easier for us to see what the answer is. So, we're going to say 12 here. So the new element would have to be 213 because 12 + 213 will give me the 225 I started with. And then here, 6 plus this negative 4 gives me 2. So it would have to be 88 here because 88 + 2 will give me back the 90 I started with. So then, we're going to say we have 88, so that is Ra, which is radium. And because we underwent a gamma emission, technically, this would be in an excited state. So, we put a little asterisk there to show that it's in an excited state. So that's all we have to do. And this top equation will be the correct way to write the equation. Remember, oops, I just combined everything. I just combined everything here to make the math easier for us to see what's going on. But it's this top equation that's the correct format that your professor would be looking for. So just remember, fundamentally, decay and emission mean the particle will be a product. Capture or absorption means it'll be a reactant. That's the key to this. And then, just remembering what's an alpha particle, a beta particle, a positron, a gamma, all those different concepts.

Here’s what students ask on this topic:

What is positron emission and how does it occur?

Positron emission is a type of nuclear decay where an unstable nucleus emits a positron, which is the antiparticle of the electron. A positron has the same mass as an electron but carries a positive charge. This process occurs when a proton in the nucleus is converted into a neutron, releasing a positron and a neutrino. The emitted positron is then ejected from the nucleus. This transformation results in the formation of a new element with an atomic number decreased by one, while the atomic mass remains unchanged.

What is the difference between positron emission and electron capture?

Positron emission and electron capture are both processes that occur in unstable nuclei to achieve stability, but they differ in their mechanisms. In positron emission, a proton in the nucleus is converted into a neutron, releasing a positron and a neutrino. In electron capture, an inner orbital electron is captured by the nucleus, where it combines with a proton to form a neutron and a neutrino. While positron emission decreases the atomic number by one, electron capture also decreases the atomic number by one but does not emit a positron.

How does positron emission affect the atomic number and mass number of an element?

During positron emission, a proton in the nucleus is converted into a neutron, resulting in the emission of a positron. This process decreases the atomic number of the element by one, as there is one less proton in the nucleus. However, the mass number remains unchanged because the total number of nucleons (protons and neutrons) stays the same. For example, if einsteinium-253 (atomic number 99) undergoes positron emission, it transforms into californium-253 (atomic number 98) while maintaining the same mass number of 253.

What are some real-world applications of positron emission?

Positron emission has several real-world applications, particularly in the field of medical imaging. One of the most notable applications is Positron Emission Tomography (PET) scans, which are used to observe metabolic processes in the body. PET scans help in diagnosing and monitoring diseases such as cancer, heart disease, and neurological disorders. In addition, positron emission is used in research to study the properties of materials and in particle physics experiments to understand fundamental particles and forces.

What is the role of a positron in nuclear reactions?

In nuclear reactions, a positron plays a crucial role in the process of positron emission, a type of beta decay. When an unstable nucleus undergoes positron emission, a proton is converted into a neutron, and a positron is emitted. The positron is the antiparticle of the electron, carrying a positive charge. Its emission results in the transformation of the original element into a new element with an atomic number decreased by one. This process helps unstable nuclei achieve greater stability by altering their proton-to-neutron ratio.