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### Course: Modern Physics (Essentials) - Class 12th>Unit 4

Lesson 1: Why are some nuclei stable and others not?

# Nuclear stability and nuclear equations

Using the ratio of neutrons to protons to figure out of a nucleus will be stable or radioactive.  Created by Jay.

## Want to join the conversation?

• Where did the extra proton come from during the decay of 14C to 14N?
• A neutron decays into a proton, emitting an electron.
• At , how does adding more neutrons cause the nucleus of the atom to be more stable? And what exactly is the 'strong force'?
• I think what Jay means is that as you add more neutrons to the nucleus the strong force is going to act, since the strong force only acts over short distances and by adding neutrons you get a denser nucleus with nucleons closer together.
• How is Cl 37 17 stable if its ratio is not 1?
• It seems that this ratio doesn't need to be precisely exact to work out. In this isotope of Cl we have a ratio of 1.17, which is pretty close to 1.
I have noticed that, even in the beginning of the periodic table, while some elements have their most stable isotopes with a ratio of 1, many of them show some slight changes, for example: Li-7 (1.3 ratio) is much more abundant than Li-6 (1 ratio);
Na-23 (1.09 ratio) counts for almost 100% of all Na... interestingly, not only is the Na-22 (ratio 1) extremely rare, but it’s unstable: it suffers a beta+ decay.
Hint: very nice to check for isotopes, their abundance and types of decay in the website: http://www.ptable.com
• Does fission count as a form of radioactive decay? It does release energy and change the nucleus
• Radioactive decay is spontaneous or natural transmutation while nuclear fission & fusion are induced transmutation/artificial with elements with an atomic number higher than 92. (Not 100% sure however).
• When you added the neutron to the carbon, shouldn't it have made it more stable as there was more strong nuclear force compared to the electrostatic force? Also why can't there be a nucleus that is composed of only neutrons?
• neutrons by themselves are not stable. They will decay into protons, with a half life of about 10 minutes
When you add a neutron to C-13 to get C-14, yes there is more strong nuclear force but you have to consider the nucleus as a whole. You have all these particles trying to find a stable arrangement. When you add one more to the pile, even if it will "stick" because of strong nuclear force, it changes the overall arrangement of all the protons and neutrons, and some arrangements are just more stable than others. Consider how C-14 decays: one of the neutrons turns into a proton. You can sort of imagine there is a neutron on the outside of the nucleus, and if it could get in and be surrounded by more particles, maybe it would be stable. But remember that free neutrons decay into protons? Well this guy on the outside is not quite free but he's not in a position to be stable. Something has to give to enable the overall state of the nucleus to become more stable. The overall arrangement becomes more stable once one of those unstable almost-free neutrons becomes a nice, stable proton, even though the proton is repelled by other protons in the nucleus. Better to be a repelled proton than an unstable neutron, basically. This is a simplification but it gives you the idea that you cannot think of each particle in isolation.
• At , how did carbon suddenly get another proton and become Nitrogen. Without an electron, it should Stay a Carbon isotope and become an ion (+1), right?
• In beta decay, one of the down quarks that composes a neutron (two down and one up quarks) in C-14 decays via the weak interaction into an up quark, leaving a proton (two up and one down quarks). The W⁻ boson from the weak interaction quickly decays into an electron and an anti-neutrino.
• It is said that the strong force comes into play when the nucleus if formed. But it did not exist before the closely packed nucleus was formed since it is a short range force. So from where does this strong force suddenly come? I mean what is its origin?
• The strong force is what holds protons and neutrons together but it is not directly responsible for holding the atomic nucleus together. The strong force is carried by particles called gluons that carry the strong charge between them but they can't exist as free particles over distances further than the size of a proton, way to short a distance to hold together an atomic nucleus. The strong charge exchange between the protons and neutrons is actually carried by virtual particles called pions that because they are virtual can only exist for a very short amount of time which limits the distance they can operate at.
• Do you have a video where you demonstrate the conversion of amu to MeVs? I'm having an issue in my homeschool physics course because I am supposed to solve, for example, E=mc^2 and write the answer in MeVs. I know that 1 amu = 931 MeV but when I tried to convert an answer from amu to MeV before, I did not get the right answer. I was wondering if you could give me an example, perhaps showing an equation and a step-by-step conversion from amu or joules to MeV.
• 1 eV = 1.6*10^-19 J.
amu is a measure of mass, not energy.
Although it is common to see something like "1 amu = 931 MeV" what they really mean is "1 amu = 931 MeV/c^2" . eV/c^2 is a measure of mass.