The ${}^8$Be nucleus and the Hoyle state in dissociation of relativistic nuclei

Abstract

The possibility of recording fragmentation events of relativistic nuclei in a nuclear emulsion, discovered back in the pioneering era of cosmic ray physics, opens up the prospect of using this method to study extremely cold ensembles of H and He nuclei in the interests of developing the physics of nuclear clustering and, possibly, expanding the scenarios of nuclear astrophysics. The results of the BECQUEREL experiment at JINR, obtained on unstable states in the relativistic dissociation of nuclei in a nuclear emulsion providing complete detection of fragments with record resolution are presented. According to the invariant masses calculated from the emission angles in the fragmentation cone, the decays of ${}^8$Be(0${}^{+}$), ${}^8$Be(2${}^{+}$), ${}^9$Be(1.7), ${}^9$B, ${}^6$Be, ${}^{12}$C(0${}_2^{+}$) or the Hoyle state and ${}^{12}$C(3${}^{-}$) have been identified. The contribution of ${}^8$Be(0${}^{+}$), ${}^9$B and ${}^{12}$C(0${}_2^{+}$) increases rapidly with the $\alpha$-particle multiplicity. Their structure and the diversity of parent nuclei suggest the fusion of the latter. The usage of automated microscopy for an analysis of exposures at the JINR NICA accelerator complex becomes a modern basis to apply the nuclear emulsion method.

The review has been prepared on the occasion of the 70th anniversary of JINR in March 2026 (https://nsr.jinr.int/)

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