Band of Stability: Electron Capture & Positron Emission - Online Tutor, Practice Problems & Exam Prep

Isotopes located to the right of the valley of stability on the neutron-to-proton plot may undergo electron capture or positron emission to achieve greater stability. These processes, although different, share the common goal of transforming an isotope with an excess of protons into a more stable form by increasing the number of neutrons relative to protons. For example, cesium-131 can either absorb an electron (electron capture) or emit a positron (positron emission) to become xenon-131, illustrating that both processes effectively convert protons into neutrons, moving the isotope towards the valley of stability. The choice between electron capture and positron emission is complex and depends on the specific isotope, but the end result is a shift towards a more stable nuclear configuration.

Band of Stability: Electron Capture

In this video, we can say that either electron capture or positron emission happens for isotopes in the right corner of the neutron to proton plot. Here we're going to say, since either process is possible, predicting which one predominates is beyond the scope of this course. Within this region, either one could happen. We're not going to delve deeply into determining which one's going to happen more so than another because there's so many isotopes and the possibilities are endless.

So here, if we take a look, we have our neutron of proton plot. We have our bed or valley of stability. This green curve here to the right of it is what we're talking about, where electron capture or positron emission can occur. Here, if we take a look, we have Cesium 131. It undergoes electron capture so it absorbs an electron. Doing this creates our daughter product of Xenon 131.

Now if we take a look here, we start out with Sesame 131 again, but doing positron emission, we let go of a positron as a product and look, we still create Xenon 131. This just highlights the fact that although they're different processes, they both have to come to the same end result. We're transforming Cesium 131 to Xenon 131.

So the basic idea here is that these isotopes, when it comes to this region, they have an excess of protons, right? So they have too many protons. The end result is the same for both processes. We're trying to convert protons into neutrons to help us shift closer to the Banner Valley of stability. So if we took a look here, what are we doing? We're trying to increase our amount of neutrons, decrease our number of protons, and in that way we move from the orange region into the green stable valley of stability.

All right? So just remember when it comes to these two processes, they're basically trying to do the same thing, but in different ways.

Band of Stability: Electron Capture & Positron Emission Example

Here it says provide the identity of the daughter nuclide created from the electron capture of strontium 80. All right, so strontium 80 is its mass number. And if we look at the periodic table, strontium has an atomic number of 38.

Electron capture means it's absorbing an electron. And remember at the end we need to have the same total mass number on both sides and the same total number of protons on both sides. Here we have 80 + 0 = 80, 38 - 1 = 37.

If we look on the periodic table, the element with an atomic number of 37 is rubidium, so we're dealing with rubidium 80, which means that option C would be our correct answer.

Provide the identity of the daughter nuclide created from the positron emission of strontium-80. 

a) Yttrium-78                  

b) Radon-81                           

c) Zirconium-82                       

d) Rubidium-80

• A. Yttrium-78
• B. Radon-81
• C. Zirconium-82
• D. Rubidium-80