Because nuclear reactions involve the breaking of very powerful intra nuclear bonds, massive amounts of energy can be released. The sum of mass and energy are conserved in nuclear decay. Therefore, a nuclear reaction will occur spontaneously when:. When the mass of the products of a nuclear reaction weigh less than the reactants, the difference in mass has been converted to energy.
There are three types of nuclear reactions that are classified as beta decay processes. The first type here referred to as beta decay is also called Negatron Emission because a negatively charged beta particle is emitted, whereas the second type positron emission emits a positively charged beta particle.
In electron capture , an orbital electron is captured by the nucleus and absorbed in the reaction. All these modes of decay represent changes of one in the atomic number Z of the parent nucleus but no change in the mass number A. Alpha decay is different because both the atomic and mass number of the parent nucleus decrease. In this article, the term beta decay will refer to the first process described in which a true beta particle is the product of the nuclear reaction.
Nuclides can be radioactive and undergo nuclear decay for many reasons. Beta decay can occur in nuclei that are rich in neutrons - that is - the nuclide contains more neutrons than stable isotopes of the same element.
These "proton deficient" nuclides can sometimes be identified simply by noticing that their mass number A the sum of neutrons and protons in the nucleus is significantly more than twice that of the atomic number Z number of protons in nucleus. The mass of the antineutrino is almost zero and can therefore be neglected. The equation above can be reached easily from any beta decay reaction, however, it is not useful because mass spectrometers measure the mass of atoms rather than just their nuclei.
The extra electron on the left cancels the mass of the beta particle on the right, leaving the inequality. The energy released in this reaction is carried away as kinetic energy by the beta particle and antineutrino, with an insignificant of energy causing recoil in the daughter nucleus.
Nuclides that are imbalanced in their ratio of protons to neutrons undergo decay to correct the imbalance. Positrons are the antiparticles of electrons, therefore a positron has the same mass as an electron but with the opposite positive charge.
I think I would fit in better, and our community of particles within the nucleus would be happier if I too were a neutron. We'd all be in a more stable condition. So what they do is, that little uncomfortable proton has some probability of emitting-- and now this is a new idea to you-- a positron, not a proton.
It emits a positron. And what's a positron? It's something that has the exact same mass as an electron. But we just write a zero there because in atomic mass units it's pretty close to zero. But it has a positive charge. And it's a little confusing, because they'll still write e there. Whenever I see an e, I think an electron. But no, they say e because it's kind of like the same type of particle, but instead of having a negative charge, it has a positive charge.
This is a positron. And now we're starting to get kind of exotic with the types of particles and stuff we're dealing with. But this does happen. And if you have a proton that emits this particle, that pretty much had all of its positive charge going with it, this proton turns into a neutron.
And that is called positron emission. Positron emission is usually pretty easy to figure out what it is, because they call it positron emission. So if we start with the same E, it has a certain number of protons, and a certain number of neutrons. What's the new element going to be? Well it's going to lose a proton. And that's going to be turned into a neutron. So p is going to go down by one. N is going to go up by one. So that the mass of the whole atom isn't going to change.
So it's going to be p plus N. But we're still going to have a different element, right? When we had beta decay, we increased the number of protons.
So we went, kind of, to the right in the periodic table or we increased our, well, you get the idea. When we do positron emission, we decreased our number of protons. And actually I should write that here in both of these reactions. So this is the positron emission, and I'm left over with one positron. And in our beta decay, I'm left over with one electron. They're written the exact same way. You know this is an electron because it's a minus 1 charge.
You know this is a positron because it has a plus 1 charge. Now there's one last type of decay that you should know about. But it doesn't change the number of protons or neutrons in a nucleus. But it just releases a ton of energy, or sometimes, you know, a high-energy proton.
And that's called gamma decay. And gamma decay means that these guys just reconfigure themselves. Maybe they get a little bit closer. And by doing that they release energy in the form of a very high wavelength electromagnetic wave. Which is essentially a gamma, you could either call it a gamma particle or gamma ray. And it's very high energy. Gamma rays are something you don't want to be around. They're very likely to maybe kill you. Everything we did, I've said is a little theoretical.
Let's do some actual problems, and figure out what type of decay we're dealing with. So here I have 7-beryllium where seven is its atomic mass. And I have it being converted to 7-lithium So what's going on here? My beryllium, my nuclear mass is staying the same, but I'm going from four protons to three protons. So I'm reducing my number of protons. My overall mass hasn't changed. So it's definitely not alpha decay. Alpha decay was, you know, you're releasing a whole helium from the nucleus. So what am I releasing?
I'm kind of releasing one positive charge, or I'm releasing a positron. And actually I have this here in this equation. So this type of decay of 7-beryllium to 7-lithium is positron emission.
Fair enough. Now let's look at the next one. We have uranium decaying to thorium And we see that the atomic mass is decreasing by 4, minus 4, and you see that your atomic numbers decrease, or your protons are decreasing, by 2. So you must be releasing, essentially, something that has an atomic mass of four, and a atomic number of two, or a helium. So this is alpha decay. So this right here is an alpha particle. And this is an example of alpha decay. Now you're probably saying, hey Sal, wait, something weird is happening here.
Because if I just go from 92 protons to 90 protons, I still have my 92 electrons out here. So wouldn't I now have a minus 2 charge? And even better, this helium I'm releasing, it doesn't have any electrons with it. It's just a helium nucleus. So doesn't that have a plus 2 charge? And if you said that, you would be absolutely correct. But the reality is that right when this decay happens, this thorium, it has no reason to hold on to those two electrons, so those two electrons disappear and thorium becomes neutral again.
And this helium, likewise, it is very quick. It really wants two electrons to get stable, so it's very quick to grab two electrons out of wherever it's bumping into, and so that becomes stable. So you could write it either way. Now let's do another one. So here I have iodine. Let's see what's happening. A positron is the antimatter version of an electron. Beta plus decay - positron emission - causes the atomic number of the nucleus to decrease by one and the mass number remains the same.
A re-arrangement of the particles in a nucleus can move the nucleus to a lower energy state. The difference in energy is emitted as a very high frequency electromagnetic wave called a gamma ray.
After emitting an alpha or beta particle, the nucleus will often still have excess energy and will again lose energy. A nuclear re-arrangement will emit the excess energy as a gamma ray.
Gamma ray emission causes no change in the number of particles in the nucleus meaning both the atomic number and mass number remain the same. Occasionally it is possible for a neutron to be emitted by radioactive decay.
This can occur naturally, ie absorption of cosmic rays high up in the atmosphere can result in neutron emission, although this is rare at the Earth's surface. Or it can occur artificially, eg the work done by James Chadwick firing alpha particles at beryllium resulted in neutrons being emitted from that.
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