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

[kiwaho]

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+.

 

[mfb]

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.

 

[kiwaho]

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.

 

[mfb]

Never all, but the fraction can get close to 1. You always have some other processes with their own cross sections competing.

 

[kiwaho]

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.

 

[snorkack]

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?

 

[mfb]

You cannot change cross sections.

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.