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Register a new userUnstable states in dissociation of relativistic nuclei. Recent findings and prospects of researches
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The invariant mass method is used to identify the $^8$Be and $^9$B nuclei and Hoyle state formed in dissociation of relativistic nuclei in a nuclear track emulsion. It is shown that to identify these extremely short-lived states in the case of the isotopes $^9$Be, $^{10}$B, $^{10}$C, $^{11}$C, $^{12}$C, and $^{16}$O, it is sufficient to determine the invariant mass as a function of the angles in pairs and triples of He and H fragments in the approximation of the conservation of momentum per nucleon of the parent nucleus. According to the criteria established in this way, the contribution of these three unstable states was evaluated in the relativistic fragmentation of the $^{28}$Si and $^{197}$Au nuclei.
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Status and prospects of nuclear clustering studies by dissociation of relativistic nuclei in nuclear track emulsion are presented. The unstable $^{8}$Be and $^{9}$B nuclei are identified in dissociation of the isotopes $^{9}$Be, $^{10}$B, $^{10}$C and $^{11}$C, and the Hoyle state in the cases $^{12}$C and $^{16}$O. On this ground searching for the Hoyle state and more complex $alpha$-particle states in the dissociation of the heavier nuclei is suggested. A detailed study of a low-density baryonic matter arising in dissociation of the heaviest nuclei is forthcoming long-term problem. An analysis of nuclear fragmentation induced by relativistic muons is proposed to examine the mechanism dissociation.
A role of the unstable nuclei ${}^{6}$Be, ${}^{8}$Be and ${}^{9}$B in the dissociation of relativistic nuclei ${}^{7,9}$Be, ${}^{10}$B and ${}^{10,11}$C is under study on the basis of nuclear track emulsion exposed to secondary beams of the JINR Nuclotron. Contribution of the configuration ${}^{6}$Be + $mit{n}$ to the ${}^{7}$Be nucleus structure is 8 $pm$ 1% which is near the value for the configuration ${}^{6}$Li + $mit{p}$. Distributions over the opening angle of $alpha$-particle pairs indicate to a simultaneous presence of virtual ${}^{8}$Be$_{g.s.}$ and ${}^{8}$Be$_{2^+}$ states in the ground states of the ${}^{9}$Be and ${}^{10}$C nuclei. The core ${}^{9}$B is manifested in the {${}^{10}$C} nucleus with a probability of 30 $pm$ 4%. Selection of the ${}^{10}$C white stars accompanied by ${}^{8}$Be$_{g.s.}$ (${}^{9}$B) leads to appearance in the excitation energy distribution of 2$alpha$2$mit{p}$ quartets of the distinct peak with a maximum at 4.1 $pm$ 0.3 MeV. ${}^{8}$Be$_{g.s.}$ decays are presented in 24 $pm$ 7% of 2He + 2H events of the ${}^{11}$C coherent dissociation and 27 $pm$ 11% of the 3He ones. The channel ${}^{9}$B + H amounts 14 $pm$ 3%. The ${}^{8}$Be$_{g.s.}$ nucleus is manifested in the coherent dissociation ${}^{10}$B $to$ 2He + H with a probability of 25 $pm$ 5% including 14 $pm$ 3% of ${}^{9}$B decays. A probability ratio of the mirror channels ${}^{9}$B + $mit{n}$ and ${}^{9}$Be + $mit{p}$ is estimated to be 6 $pm$ 1.
The dissociation of relativistic $^{12}$N nuclei having a momentum of 2 GeV/c per nucleon and undergoing the most peripheral interactions in a track emulsion is studied. The picture of charged topology of product ensembles of relativistic fragments and special features of their angular distributions are presented.
In the context of the search for triples of relativistic $alpha$-particles in the Hoyle state, the analysis of available data on the dissociation of the nuclei ${}^{12}$C, ${}^{16}$O and ${}^{22}$Ne in the nuclear emulsion was carried out. The Hoyle state is identified by the invariant mass calculated from pair angles of expansion in $alpha$-triples in the approximation of the conservation of the momentum per nucleon of the parent nucleus. The contribution of the Hoyle state to the dissociation of ${}^{12}$C $to$ 3$alpha$ is 11%. In the case of the coherent dissociation of ${}^{16}$O $to$ 4$alpha$ it reaches 22% when the portion of the channel ${}^{16}$O $to$ 2${}^{8}$Be is equal to 5%.
Possibilities of the nuclear emulsion technique for the study of the systems of several relativistic fragments produced in the peripheral interactions of relativistic nuclei are discussed. The interactions of the $^{10}$B and $^{9}$Be nuclei in emulsion are taken as an example to show the manifestation of the cluster degrees of freedom in relativistic fragmentation. For the case of the relativistic $^{9}$Be nucleus dissociation it is shown that exact angular measurements play a crucial role in the restoration of the excitation spectrum of the alpha particle fragments. The energy calibration of the angular measurements by the $^{9}$Be nucleus enables one to conclude reliably about the features of internal velocity distributions in more complicated systems of relativistic $alpha$ particles.
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