How many barns above could make nuclear reaction rate 100%?

In summary, cross section is important for the possibility of a reaction and can span a wide range of values. There is no direct relation between cross section and reaction rate. Cross section ratios and small cross sections, such as those for Higgs and dark matter, are not uncommon. The fraction of particles consumed in a reaction can approach 1, but there are always competing processes. Positron capture is a rare reaction and cross sections cannot be manually increased.
  • #1
kiwaho
72
1
All guys know the importance of cross section. In a sense, it stands for the possibility of a reaction.
I am wondering how many barns above could make nuclear reaction rate almost 100%?
Generally speaking, the cross section can span a couple of decades order of magnitude, e.g. 10^-10 to 10^6 barns.
I speculate the answer maybe 100Kb+.
 
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  • #2
There is no direct relation between a cross section and a reaction rate. Also, what does "100%" mean: 100% of what?
You might be interested in cross section ratios.

Cross sections like 10-15 barns are not unusual for things like Higgs in specific decay channels or double Higgs production, and dark matter cross sections are even smaller.
 
  • #3
mfb said:
There is no direct relation between a cross section and a reaction rate. Also, what does "100%" mean: 100% of what?
You might be interested in cross section ratios.

Cross sections like 10-15 barns are not unusual for things like Higgs in specific decay channels or double Higgs production, and dark matter cross sections are even smaller.
For example, 7Li(p,n)7Be, at 1910Kev of proton beam, the cross section 590mb, statistics shows every 100,000 protons, only 1 proton is used in the said reaction. So I guess if a reaction with 100,000b above cross section, then all bombarding protons will be consumed in reaction.
 
  • #4
Never all, but the fraction can get close to 1. You always have some other processes with their own cross sections competing.
 
  • #5
mfb said:
Never all, but the fraction can get close to 1. You always have some other processes with their own cross sections competing.
Is there a way to manually increase specific cross section? Looking up recognized data table, always feel disappointed with those so tiny sigma.
 
  • #6
An example of a reaction with fraction very close to 1 is positron annihilation. Positron is stable, so it has few options other than annihilation.
How common reaction is positron capture?
 
  • #7
You cannot change cross sections.
snorkack said:
How common reaction is positron capture?
Positrons have a positive charge, so at low energies the probability is "zero". At high energies, inelastic reactions have a higher probability.
 

1. How many barns above are required to achieve a 100% nuclear reaction rate?

The number of barns above required to achieve a 100% nuclear reaction rate depends on several factors, including the type of nuclear reaction, the type of particles involved, and the energy level of the particles. In general, a larger number of barns above are needed for a higher energy reaction.

2. Can a 100% nuclear reaction rate be achieved with a small number of barns above?

In most cases, it is not possible to achieve a 100% nuclear reaction rate with a small number of barns above. This is because the probability of a nuclear reaction occurring increases with the number of target particles present. Therefore, a larger number of barns above are needed to increase the chances of a nuclear reaction taking place.

3. What is the relationship between the number of barns above and the nuclear reaction rate?

The number of barns above is directly proportional to the nuclear reaction rate. This means that as the number of barns above increases, the nuclear reaction rate also increases. However, there may be other factors at play that can affect the overall nuclear reaction rate.

4. Are there any other factors besides the number of barns above that can affect the nuclear reaction rate?

Yes, there are several other factors that can affect the nuclear reaction rate, such as the temperature and pressure of the particles involved, the type of particles, and the presence of other substances that may interfere with the reaction. These factors must also be taken into consideration when trying to achieve a 100% nuclear reaction rate.

5. Can a 100% nuclear reaction rate be sustained indefinitely?

No, a 100% nuclear reaction rate cannot be sustained indefinitely. This is because as the reaction rate increases, the particles involved will eventually run out of energy and the reaction will slow down or stop completely. Additionally, there may be other factors, such as the decay of particles or the depletion of reactants, that can also affect the sustainability of a 100% nuclear reaction rate.

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