Friday 5 June 2020

electromagnetic radiation - Will a free neutron radiate if it is decelerated?



In this answer it is said (and I fully agree):



Yes, a ... photon can accelerate a lone neutron. The kinetic energy imparted to the neutron reduces the photon's wavelength (redshifts it) by the same amount, so the total energy of the system remains the same.



In turn, the opposite process has to be possible too. Neutrons are able to radiate. This usually is said only for charged particles.




Electromagnetic waves are emitted by electrically charged particles undergoing acceleration, and these waves can subsequently interact with other charged particles Electromagnetic radiation





Will a free neutron radiate if it is decelerated?



Answer



The neutron is magnetic. It is a tiny little magnet. In more formal language, it carries a magnetic dipole moment of size $$ \mu_n = −9.6623647(23) \times 10^{−27} {\rm J\,T}^{−1}. $$ This is what allows it to interact with electromagnetic waves---or, to say the same thing another way, with photons. This also means that when accelerated then yes, it will generate electromagnetic radiation. This effect is much smaller that the radiation of a charged particle with the same acceleration.


You can associate this radiation with the presence of accelerating charge, indirectly, by noting that the neutron has charged quarks inside it, but strictly speaking those components have to be treated by quantum theory so they shouldn't be thought of as little separate charges. The calculation in terms of magnetic dipole moment is more appropriate.


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