- #1

CAF123

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I then attempted a small question:

Deduce the de Broglie wavelength of thermal neutrons from a nuclear reactor which have k.E ~(3/2)kT.

I have the correct answer and know how to solve the problem (which is why I did not post in homework forum), however, I found the answer by finding k.E by the above formula and then equating this to (1/2)mV^2 and solving for v. After finding v, I found p = mv and therefore the de Broglie wavelength.

My question is: when I instead use the relativistic eqn at the top (which according to my notes works in all frames of references) I yield a negative under the square root. Why is this so? Why aren't things consistent?

For reference, I used E = 6.1 x10^-21 J in both attempted methods.

Many thanks