Calculate velocity of a 1MeV Neutron

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    Neutron Velocity
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Discussion Overview

The discussion revolves around calculating the velocity of a neutron with a kinetic energy of 1 MeV. Participants explore the implications of this energy in relation to the neutron's rest mass and the appropriate equations to use for the calculation, considering both relativistic and non-relativistic approaches.

Discussion Character

  • Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant questions how to calculate the velocity of a 1 MeV neutron, noting that using the formula for velocity results in a square root of a negative number.
  • Another participant clarifies that the 1 MeV refers to kinetic energy, not total energy, suggesting that the rest mass energy should be considered separately.
  • A participant expresses uncertainty about whether the 'E' in the equation refers to the total energy (rest plus kinetic) or just the kinetic energy.
  • It is proposed that since the neutron's rest mass exceeds 1 MeV, it is reasonable to assume that the kinetic energy is indeed what is meant in this context.
  • One participant suggests using the non-relativistic kinetic energy formula E=(mv^2)/2 to estimate the velocity, proposing a value of v as a fraction of the speed of light.
  • Another participant agrees with the non-relativistic approach, indicating it is a good approximation given the energy involved.

Areas of Agreement / Disagreement

Participants generally agree that the 1 MeV refers to kinetic energy and that the rest mass energy should be considered. However, there is no consensus on the best approach to calculate the velocity, with differing opinions on the appropriateness of non-relativistic versus relativistic methods.

Contextual Notes

There are unresolved assumptions regarding the definitions of energy in the context of the equations being used, and the applicability of non-relativistic formulas given the neutron's rest mass energy.

rem45
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How would one calculate the velocity of a 1MeV neutron??

I tried the following the attached formula for V/C but E is less than the rest mass which yields the square root of a negative number. Not sure what to do for this
 

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1 MeV here is surely the kinetic energy, not the total (rest plus kinetic) energy.
 
It doesn't say. I guess that I will assume such. Is the 'E' in the equation I am using for the rest mass energy plus the kinetic energy?
 
Since a neutron has a higher rest mass than 1MeV, then one should safely assume that kinetic energy is what is meant here.

The E in that equation is indeed the rest+kinetic energy.
 
Since the neutron rest mass is approximately 940 Mev, you probably could use E=(mv^2)/2 to get v. (v=c/22?).
 
Last edited:
mathman said:
Since the neutron rest mass is approximately 940 Mev, you probably could use E=(mv^2)/2 to get v. (v=c/22?).
I agree that a nonrelativistic approach should be fine - it is a very good approximation.
 

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