What happens when two neutrons collide and what particles might be produced?

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    Collision Neutron
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Discussion Overview

The discussion explores the outcomes of collisions between neutrons, including the energy levels required for various interactions and the particles that may be produced. It touches on concepts from particle physics, such as the Pauli exclusion principle, neutron decay, and quark interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Gregor questions the implications of the Pauli exclusion principle on neutron collisions and the energy required for interactions.
  • Bill_K clarifies that the Pauli principle allows neutrons with opposite spins to occupy the same space and discusses the nature of particle collisions, including the exchange of virtual particles and the role of pions in neutron interactions.
  • Gregor expresses interest in the outcomes of neutron collisions, particularly when considering the quark composition of neutrons and asks for resources on understanding quark interactions.
  • Another participant notes that for an electron to be captured by a proton, it must have sufficient kinetic energy (at least 1.3 MeV) to allow for the conversion back into a neutron and an anti-neutrino, or it could result in elastic scattering or hydrogen atom formation.
  • It is suggested that at low energies, neutron collisions may result in scattering without producing new particles, while high-energy collisions could yield various hadrons, including pions, as long as charge and baryon number are conserved.
  • One participant mentions that with sufficiently energetic collisions, quarks and gluons behave more independently, leading to the formation of hadrons from the resulting interactions.

Areas of Agreement / Disagreement

Participants present multiple competing views regarding the outcomes of neutron collisions, the implications of the Pauli exclusion principle, and the conditions necessary for electron capture by protons. The discussion remains unresolved with differing interpretations and hypotheses.

Contextual Notes

There are limitations regarding the assumptions made about neutron interactions, the energy thresholds for various processes, and the specific conditions under which certain outcomes may occur. The discussion does not resolve these complexities.

GregorSch
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Hi,

1)
I have recently read a book about particle physics and was wondering
what could happen if two neutrons hit each other and what energy level would be required for what ever happens?
(Since the Pauli exclusion principle does not allow two neutrons to be at the same time and space).

2)
If a neutron splits into a proton, electron and an anti-neutrino
n→p+e−+νˉe
why is the electron not flying into the proton or building a two particle cloud with the proton until thy might fall apart?

please help the noob and thx,

Gregor.
 
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OK, several things. First of all the Pauli principle only says that the overall wavefunction of the two particles is antisymmetric. This includes the spin, so if the particles have opposite spin (spin up and spin down) they are allowed to be at the same point in space.

Secondly, most collisions between particles are indirect, that is they exchange a virtual particle. Inside nuclei, where neutrons constantly interact, they can be thought of as exchanging pions.

Third, neutrons aren't elementary. On a more fundamental level a neutron-neutron collision would actually be between a pair of quarks.

Regarding the second question, the neutron's mass is 939.5 MeV/c2 while the proton's mass is 938.2 MeV/c2. This leaves 1.3 MeV/c2 worth of kinetic energy to propel the decay products rapidly apart.
 
Hi Bill_K, that is so kind of you, thank you.

2) I also looked up some Feynman diagrams and my question is solved. I should have asked, what happens, when an electron gets captured by a proton.

1)
Lets say two neutrons with the same spin or a different spin that were created by stripping of the proton, even thought they are unstable, would collide. What could happen? The only Feynman diagram I could find was:
http://www2.warwick.ac.uk/study/csd...research/phdresearch/theory/betadecay/double/

Nah, I will just have to understand quark interaction. Is there a good book?

udd + udd -> ?thx,

Gregor.
 
Last edited:
when an electron gets captured by a proton.
It can't! Not unless it arrives with at least 1.3 MeV (see above) of kinetic energy, in which case they can turn back into n + νe. Lacking this much energy, they could elastic scatter, or conceivably form a hydrogen atom.

What would happen if two neutrons collide? Again at low energy they could just scatter: n + n → n + n. With plenty of energy available they could produce anything you can think of, just so's the total charge is conserved (zero) and the baryon number (two). Pions are popular. So for example,

n + n → p + p + π- + π- + π- + π+
 
Neutrons are strongly interacting, thus, colliding neutrons will most likely produce whatever hadrons are above threshold, whatever ones have masses lower than the available energy. That includes pions, as Bill_K had mentioned.

With energetic-enough collisions, the quarks and gluons in them start acting like more-or-less independent entities, colliding with each other more-or-less separately. However, the quarks and gluons that emerge then form hadrons.
 

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