Beta Decay - Video Tutorials & Practice Problems

Beta Decay

Now beta decay occurs when an unstable nucleus emits a beta particle. Now what is a beta particle? Well, a beta particle is a high energy and high speed electron. Now, if we're talking about an electron, we can symbolize in two different ways. So here electrons remember are very small compared to neutrons or protons. Their weight is so small that it's almost insignificant. So we have a mass number of zero for them electrons are negatively charged. So we have minus one here in the atomic number slot here, we could symbolize it by E for electron or we can say it's a beta particle. So we use the beta symbol. Now here this usually occurs in nuclei with an excess number of neutrons when we do beta decay. What we, what are we trying to do? Well, when we do beta decay, we're trying to actually bring down our number of neutrons and we're trying to increase our number of protons and we're trying to balance them out with each other. Since we have an excess of neutrons, we need to get rid of some of those neutrons. And we do this by converting them into protons now, neutrons split into a proton and an electron the electron is ejected from the nucleus. So here we're basically bringing down a number of neutrons to help us increase our number of protons in the process. We also eject an electron from the nucleus, the uh the electron from the nucleus. But the proton that's created stays within the nucleus. Here we have what we have selenium 81 it's gonna undergo beta decay. So we're ejecting our electron. And remember when it comes to our mass number, it has to be the same on both sides. And our total number of protons has to be the same on both sides. Here, we have 81 as our mass number. So on the product side, we need to have a total mass number of 81 as well. Well, the electron doesn't contribute anything to that. So our new isotope would still have a mass number of 81. On the reactant side, we have 34 protons. So on the product side, we need to have 34 protons. But here we have a minus symbol, subtracting minus one. So to get 34 on the product side, I actually have to add 35 here because 35 minus one gives me 3434 protons just like the reactant side. And if we look at the periodic table, what's the only element that has an atomic number of 35 be bro me. So we converted selenium 81 into bromine 81 by way of beta decay. And so this will represent our beta decay reaction.

Beta Decay Example

Here, it says to write a balanced nuclear reaction for beta decay of iodine 129 right. So iodine 129 if we look on the periodic table, iodine has an atomic number of 53 beta decay means that our energetic particle in this case, the electron will be a product. Remember, the mass numbers on both sides have to be the same, the total number of protons on both sides have to be the same here. This would still be 129 because 129 plus zero gives me 129. On the reactant side, we have 53 protons. So on the product side, we also need 53 protons. The number you would have to be 54 because 54 minus one gives me 53. Now, if we look on the periodic table, what element has an atomic number of 54? That's right. It will be zenon. So here we'd say that iodine 129 turns into xenon 129 by way of beta decay. So this represent our beta decay reaction of iodine 129

Characteristics of Beta Particles

Now, when it comes to the characteristics of beta particles, we can compare them to alpha particles. Here, we can say the beta particles are much smaller than alpha particles. That's because an alpha particle is uh basically a helium four isotope pretty large. We have two protons and two neutrons, whereas a beta particle is only an electron incredibly small. Now, here we'd say that they, they're going to have lower ionizing power. If an alpha particle were to get inside of biological tissue, since it's so large, it'll move much more slowly giving it time to ionize all surrounding tissue. Beta particles being electrons move very rapidly. So they go through the material much quicker, not giving themselves ample time to ionize all biological tissue. And as a result of this, because they're so much smaller because they can move faster. We can say that beta particles have a higher penetrating power. If we continue looking at this chart down below, we're gonna say we have our alpha decay of platinum, 171 that gave us 167 for osmium for beta decay, we have selenium 81 becoming bromine 81 in terms of size. Alpha particles are the largest because they're represented by the helium four isotope or beta particles. They're going to be smaller. In comparison, ionizing power. A of particles have the highest we're gonna say here that in comparison, beta particles are lower penetrating power since alpha particles are the largest, they have very slow penetrating power. We're gonna say here that beta particles in comparison are higher. Now what can shield us if the penetrating power is higher for a beta particle? Well, here we need much more dense material. So like a sheet of metal or a thick chunk of wood. OK. So we need more dense material to stop the progression of a beta particle. So just remember we can compare these 2 to 1 another. Remember size of them can contribute a lot to our ideas of ionizing power and penetrating power.

Beta Decay Example

Which are not the characteristics of beta decay. Beta particles are smaller in size but have higher ionizing power due to their speed. This is not true. Yes, they're smaller in size. But because they're smaller in size, they move much more quickly, giving them less time to ionize tissue that they enter. So they would have lower ionizing power. So this is our answer. Let's look at the other options. A high energy high speed electron is ejected from a nucleus of an unstable app. That's true due to higher penetrating power, beta particles can be blocked by yours cannot be blocked by your skin. That is also true. You need thicker material. Beta particles carry a mass number of zero. Yes, a beta particle is an electron. So it's zero over negative one and then your electron. So here, the only statement that's not true. Not a characteristic of beta decay is option A.