The spent fuel elements from a fission reactor are much more intensely radioactive than the original fuel elements. (b) Given that only two or three neutrons are released per fission event and knowing that the nucleus undergoing fission has a neutron-to-proton ratio characteristic of a heavy nucleus, what sorts of decay would you expect to be dominant among the fission products?

Video transcript

welcome back everyone. The radio activity from a vision reactor is substantially higher than that of the initial fuel. What types of decay would you anticipate to be predominant among the fission products given that only two or three neutrons are generated per fission event. And knowing that the nucleus undergoing fission has a neutron to proton ratio typical of a heavy nucleus. So by heavy nucleus, what this statement is referring to is our atom which should have an atomic number, which we recall is represented by the symbol Z. That is greater than we're going to say from the atomic number on our X axis, going from 83 up Those will be the heavier atoms or heavier nucleus is. And so with atomic numbers greater than 83, we have a higher proton to neutron ratio. So let's focus on what this diagram is telling us right now we know that our starting new glide or starting nucleus is uranium, specifically the isotope of uranium We'll say 2 35. So uranium 2 35 is our starting nucleus. And according to our Diagram, we get from uranium to 35 to thorium as our next product. And we'll say that this is thorium To thorium 2 31 as a product. New Clyde. And so what we should recognize is that we went down by four units. So we decreased by four atomic mass units. Recall that in our or on our Y axis. These values given in our isotope names that we've written are the mass numbers. And so it makes sense that we decrease by four atomic mass units. Now we want to think of what particle causes this. So we want to recall that this is caused by our particle which we should recall as the only one that causes a change in mass number which is our alpha emission. And so we have an alpha mission that occurred where we produced a helium particle or specifically a helium four particle, which is our particle for the alpha emission, which has an atomic number of two. So we can say that this uranium 2 35 underwent an alpha emission to form thorium 2 31. And now from thorium 2 31 we're told that our next product new glide is palladium to 31 because it's in the same row as story. Um So it has the same mass number. And so because we maintained the same mass number, but looking at our X axis, we have an increase by one unit in atomic number two. Now, palladium 231 with the Atomic # 91. This is an increase in atomic number by one unit. And we want to recall that to increase in an atomic number by one unit. The particle involved would be our beta particle. And so we would see that to go from thorium to To palladium to 31 Where palladium to 31 has the atomic number of 91 thorium has the atomic number of we would say and will actually draw an arrow here. We'll say that thorium 2 31 underwent a beta emission. And so we're going to form as a product. A beta particle which we recall has a atomic number of minus one and a mass number of zero. And this beta particle or beta emission causes our thorium 2 31 to form our palladium to with a higher Atomic number by one unit. So we said this is beta emission. So so far we can confirm that as we go higher in atomic number. So let's write this out higher atomic number with no change in atomic mass. We can confirm that this will give us or that this is caused rather by beta emission. Now we go back to a decrease in our atomic mass following. And let's use the right pen. So following the trend of our graph here we go back to a decrease in atomic mass, meaning that we have mostly alpha emissions occurring here. As we stated, because we know that alpha emissions decrease our product by four atomic mass units. So we see that trend of alpha emissions occurring here. And then once we get to this end product of our vision reactor here, we have our products here that form. So we'll say these are our products of the nuclear fission. We want to now make note of where our band of stability is. And recall that our band of stability is where we no longer have any reactions occurring to produce any more products. And that would be where we see lead specifically lead 203 Is where we see no more reactions occurring, no more products being produced. And it would be where this lead 203 is is where our band band of stability is located at. So let's thought that in this is going to be where our band of stability is at. So band of stability. And according to our prompt, the radio activity of our spent fuel is higher than the radio activity of our initial fuel. And that is why we see all of our products lying outside of our band of stability here. And sorry about that. So they're all lying outside of our band of stability here on the left. Now looking at these products here, we can see that as we stated, when we have a lack of change in mass number or atomic mass, but an increase in atomic number which is our Z value as we stated, And we are seeing an increase in atomic number between business and polonium where we have polonium 84 and business business 83. And we began with lead 82. We know that that means we have a beta emission occurring and so it would make sense that our products of this vision reaction undergo beta decay and they have to go this beta decay. They have to go through beta decay in order to decrease our ratio of protons to neutrons because we have associated with these products with a high consistent mass but low range of or sorry, rather increasing range of atomic number, our ratio of protons to neutrons becomes worse because we'll have still a large amount of neutrons compared to protons when you take the difference. Because again, recall that mass number is the difference between or it's calculated rather by taking our protons added to our neutrons. And so if we know that atomic number which we recall is, Z tells us our number of protons, we take the difference between the mass number and our number of protons for these products. You'll see that we'll have a large number of neutrons for these products here. So they must undergo this beta decay to decrease that ratio so that we can even that ratio out. We also should recognize that we might have some gamma decay occurring which comes from our decrease in atomic mass or mass number. Since we see we go from lead to 11 to around lead 203. This decrease in atomic number we recall is caused by alpha emissions releasing beta particles and or sorry, releasing helium particles here and with the release or ejection of these helium particles caused by these alpha emissions that would relate to the high energy of our products which will ultimately always release gamma radiation since they're such high energy recall that things with high energy will often give off gamma radiation. But for our main final answer to complete this example, we're going to confirm that the primary type of decay that we're going to anticipate seeing among our fission products is going to be our beta decay. So beta decay is our final answer. I hope everything I reviewed was clear. If you have any questions, please leave them down below and I will see everyone in the next practice video.