Spontaneous generation of the Dicke superradiation (SR) state has been found in the system of inversely polarised proton spins with “frozen” polarisation. SR is observed at the moment when the Larmor frequency crosses the resonance frequency of the passive oscillatory circuit. SR arises from incoherent maser generation of spins. The frequency of a SR generator can be retuned from several hundreds of kilohertz to hundreds of megahertz at very low temperatures. Dependence of incoherent and coherent radiation on the initial polarisation has been investigated. A radio frequency analogue of the optical SR laser is shown to be possible both for weak-amplifying and for strong-amplifying active media, depending on the factor of filling and polarisation of nuclei. SR-reverse of negative polarisation is observed in the latter case.
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