Q values for strong weak and EM interactions?

In summary, Q values refer to the energy released or absorbed during a nuclear or subatomic particle reaction. Strong interactions have the highest Q values, followed by weak interactions and then electromagnetic interactions. Q values are calculated using the mass difference between initial and final states, based on Einstein's famous equation E=mc^2. They play a crucial role in determining the stability and likelihood of nuclear reactions, with positive Q values indicating exothermic reactions and negative Q values indicating endothermic reactions. Q values differ between interactions, with strong interactions having the highest values due to the strong force being the strongest fundamental force. And finally, Q values can be negative, indicating endothermic reactions that require energy to occur.
  • #1
philip041
107
0
I have just read, in general, weak interactions, have the lowest Q values; meaning they have the smallest cross sections, which means they control processes in stars at some time in the early universe.

What would be the next relative strength?

Cheers
 
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  • #2
The Q-value just tells you how big phase space you'll have, the density of final states. Now there is more things that governs the cross section, the interaction matrix amplitude. And that is, the interaction itself, that turns the initial state into the final state.
 
  • #3
Cheers, I think I am probably going to fail my exam, thanks anyway!
 

1. What are Q values for strong, weak, and EM interactions?

Q values refer to the energy released or absorbed during a nuclear or subatomic particle reaction. For strong interactions, Q values are typically high, indicating the large amount of energy released when quarks interact. Weak interactions have lower Q values, while electromagnetic (EM) interactions have the lowest Q values.

2. How are Q values calculated?

Q values are calculated using the mass difference between the initial and final states of a nuclear or subatomic particle reaction. This is based on Einstein's famous equation, E=mc^2, which relates energy (E) to mass (m) and the speed of light (c). The difference in mass is then converted to energy, giving the Q value.

3. What is the significance of Q values in nuclear reactions?

Q values play a crucial role in nuclear reactions as they determine the stability and likelihood of a reaction occurring. If the Q value is positive, the reaction is exothermic and will release energy, making it more likely to occur. If the Q value is negative, the reaction is endothermic and will require energy to occur, making it less likely.

4. How do Q values differ between strong, weak, and EM interactions?

As mentioned earlier, Q values for strong interactions are typically higher than those for weak and EM interactions. This is due to the strong force being the strongest of the fundamental forces, thus requiring more energy to overcome. Weak interactions have lower Q values as they involve the exchange of intermediate particles, which have less mass and therefore less energy. EM interactions have the lowest Q values as they are mediated by photons, which have no mass.

5. Can Q values be negative?

Yes, Q values can be negative in certain nuclear reactions. This indicates that the reaction is endothermic and will require energy to occur. An example of this is in nuclear fission reactions, where a heavy nucleus splits into two smaller nuclei, releasing energy in the process. However, if the initial nucleus is not heavy enough to overcome the strong force, the Q value will be negative, and the reaction will not occur spontaneously.

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