Formation of hypernuclei in evaporation and fission processes

There are excellent opportunities to produce excited heavy hyperresidues in relativistic hadron and peripheral heavy-ion collisions. We investigate the disintegration of such residues into hypernuclei via evaporation of baryons and light clusters and their fission. Previously these processes were well known for normal nuclei as the decay channels at low excitation energies. We have generalized these models for the case of hypermatter. In this way we make extension of nuclear reaction studies at low temperature into the strange sector. We demonstrate how the new decay channels can be integrated in the whole disintegration process. Their importance for mass and isotope distributions of produced hyperfragments is emphasized. New and exotic isotopes obtained within these processes may provide a unique opportunity for investigating hyperon interaction in nuclear matter.

Figure 1

Fragment mass distributions produced after disintegration of ${}^{209}\mathrm{Bi}$ excited normal nuclear systems. Excitation energies are given in panels (a), (b), and (c). The calculations include all decay processes for heavy nuclei: The contributions of fission (dashed blue lines) and evaporation (red dot-dashed lines) of the initial compound nuclei are shown separately. The rest to the total yields (solid lines with black circles) belong to the contribution of multifragmentation process.

Figure 2

The same as in Fig. 1 but for higher excitation energies.

Figure 3

Probability of the nuclear fission (circles, solid lines) and surviving the compound nucleus after evaporation of light particles (squares, dashed lines) versus excitation energy of nuclei. The nuclei are noted at the panels (a), (b), and (c).

Figure 4

Probability of the hypernuclear fission (solid circles, solid lines) and surviving the compound hypernucleus after evaporation of light particles (solid squares, dashed lines) versus excitation energy of hypernuclei. The solid triangles (dotted lines) give the probability for emission of single $\mathrm{\Lambda }\text{-hyperons}$. The initial compound hypernuclei are noted in panels (a), (b), and (c).

Figure 5

Probability of the evaporation of light hypernuclei from heavy compound hypernuclei (see panels) versus excitation energy. The notations for evaporated nuclei (symbols and lines) are given in panels (a), (b), and (c).

Figure 6

Average mass numbers [top panel (a)] and charges [bottom panel (b)] for the fissioning ${}_{\mathrm{\Lambda }}{}^{209}\mathrm{Bi}$ hypernuclei at the saddle point (noted as hot, red circles), and for final nuclear remnants after their deexcitation (noted as cold, black squares), versus the excitation energy. The statistical deviations are shown by error bars.

Figure 7

The average excitation energy [$E^{*}$ (a)] and the fission barrier [$B_f$ (b)] of the fissioning ${}_{\mathrm{\Lambda }}{}^{209}\mathrm{Bi}$ hypernuclei at the saddle point (noted as hot) versus initial excitation energy. The remaining excitation energy of fission remnants is given in panel (a) too. Other notations are as in Fig. 6.

Figure 8

Mass distributions of fission and evaporation hyperfragments after disintegration of ${}_{\mathrm{\Lambda }}{}^{238}\mathrm{U}$ hypernuclei at different excitation energies $E_x$ [in MeV per nucleon; see panels (a), (b), and (c)]. The calculations include the competition of evaporation and fission decay modes.

Figure 9

The same as in Fig. 8, however, for ${}_{\mathrm{\Lambda }}{}^{209}\mathrm{Bi}$ excited hypernuclei.

Figure 10

Probabilities of the yield (normalized per one event) of single hypernuclei produced after evaporation and fission of the excited initial ${}_{\mathrm{\Lambda }}{}^{238}\mathrm{U}$ hypernucleus. The squares present the nuclei in the plane of the charge number $\left(Z\right)$ neutron number $\left(N\right)$. The location of stable normal nuclei (from the nuclear chart) are represented by the dark circles to facilitate the comparison. Colors of the squares corresponding to the calculated ranges of the probability $p$ of these hypernuclei are given in the figure. Excitation energies are noted in panels (a) and (b).

Figure 11

The same as in Fig. 10, however, for the initial ${}_{\mathrm{\Lambda }}{}^{209}\mathrm{Bi}$ hypernucleus.

Figure 12

Probabilities of the yield (normalized per one event) of single hypernuclei produced after evaporation and fission of the excited initial ${}_{\mathrm{\Lambda }}{}^{112}\mathrm{Sn}$ (a) and ${}_{\mathrm{\Lambda }}{}^{124}\mathrm{Sn}$ (b) hypernucleus at the excitation energy 0.5 MeV per nucleon. The circles present the nuclei in the plane of the charge number $\left(Z\right)$ neutron number $\left(N\right)$. The locations of stable normal nuclei (from the nuclear chart) are represented by the empty squares. Colors of the circles corresponding to the calculated ranges of the probability $p$ of these hypernuclei are given in the figure.

Figure 13

The same as in Fig. 12, however, for the excitation energy 2 MeV per nucleon.