Theory of $\beta -$ emission exclusively considers participation of one $W -$ boson, one electron and one electron-antineutrino, but no photons. However Maxwell's electrodynamics require that during any change of an electromagnetic field, EM-radiation (photons) must be emitted. Spontaneous separation of two oppositely charged particles generates a variable electric dipole field which should emit EM-radiation. Moreover, as the emitted electron is strongly decelerated in the Coulomb field this also should generate EM-radiation. However, spin angular momentum conservation would require pairwise emission of photons with mutually opposed spin (sum $+1 - 1 = 0$). To my knowledge such EM-radiation has never been reported or predicted.
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$\begingroup$ Does the resultant nuclei-electron orbital change count? $\endgroup$– honeste_vivereCommented Sep 8, 2017 at 17:02
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It has been reported, predicted, and even used to place an upper bound on the neutrino mass. My background is condensed matter so I may be very wrong about these sorts of particle-physics topics: but I believe the presence of a large nucleus nearby probably breaks your expectation of pairwise emission. (Pairwise emission is however a well-known and common feature of positron annihilation, where the opposite-directionality is used by PET scanners to filter out high-energy photons coming from non-positron sources.)
The reason that a first romp through the literature might not have revealed this to you is most likely that you do not have a particle physics background; this sort of electron-braking radiation is known to particle physicists by its German name bremsstrahlung even in English publications. More specifically the bremsstrahlung from the inside of the nucleus is known as "inner bremsstrahlung"; this search phrase leads to many discussions of the phenomenon, and even a mention on Wikipedia.
