Properties of the initial participant matter interaction zone in near-Fermi-energy heavy-ion collisions

The sizes, temperatures, and free neutron-to-proton ratios of the initial interaction zones produced in the collisions of 40 MeV/nucleon ${}^{40}\mathrm{Ar}$+${}^{112}\mathrm{Sn}$ and 55 MeV/nucleon ${}^{27}\mathrm{Al}$+${}^{124}\mathrm{Sn}$ are derived using total detected neutron plus charged particle multiplicity as a measure of the impact parameter range and number of participant nucleons. The size of the initial interaction zone, determined from a coalescence model analysis, increases significantly with decreasing impact parameter. The temperatures and free neutron-to-proton ratios in the interaction zones are relatively similar for different impact parameter ranges and evolve in a similar fashion.

Figure 1

Total detected multiplicity of charged particles and neutrons observed with the NIMROD detector. Dashed lines indicate the multiplicity bins selected for the analysis. (a) 40 MeV/nucleon ${}^{40}\mathrm{Ar}$ + ${}^{112}\mathrm{Sn}$ (b) 55 MeV/nucleon ${}^{27}\mathrm{Al}$ +${}^{124}\mathrm{Sn}$.

Figure 2

Mass emitted from the IV source as nucleons and light clusters plotted as a function of $A_{\mathrm{part}}$ determined from Glauber model calculations. Results are presented for 40 MeV/nucleon ${}^{40}\mathrm{Ar}$ + ${}^{112}\mathrm{Sn}$ (solid squares) and 55 MeV/nucleon ${}^{27}\mathrm{Al}$+${}^{124}\mathrm{Sn}$ (solid diamonds).

Figure 3

${}^3\mathrm{H}$/${}^3\mathrm{He}$ ratios as a function of surface velocity. Symbols of open circles, solid squares, open triangles, and solid circles correspond, respectively, to progressively increasing total neutron plus charged particle multiplicity. (a) 40 MeV/nucleon ${}^{40}\mathrm{Ar}$+${}^{112}\mathrm{Sn}$; (b) 55 MeV/nucleon ${}^{27}\mathrm{Al}$+${}^{124}\mathrm{Sn}$. See text and Fig. 1 for details.

Figure 4

$P_0$ as a function of $V_{\mathrm{surf}}$ for 55 MeV/nucleon ${}^{27}\mathrm{Ar}$+${}^{124}\mathrm{Sn}$. Results are presented for ${}^2\mathrm{H}$ (upper left), ${}^3\mathrm{H}$ (upper right), ${}^3\mathrm{He}$ (lower left), and ${}^4\mathrm{He}$ (lower right). In each case data are presented for four selected windows. Symbols of open circles, solid squares, open triangles, and solid circles correspond, respectively, to progressively increasing total neutron plus charged particle multiplicity See text.

Figure 5

$P_0$ as a function of $V_{\mathrm{surf}}$ for 40 MeV/nucleon ${}^{40}\mathrm{Ar}$+${}^{112}\mathrm{Sn}$. Results are presented for ${}^2\mathrm{H}$ (upper left), ${}^3\mathrm{H}$ (upper right),${}^3\mathrm{He}$ (lower left), and ${}^4\mathrm{He}$ (lower right). In each case data are presented for four selected windows. Symbols of open circles, solid squares, open triangles, and solid circles correspond, respectively, to progressively increasing total ejectile multiplicity. See text.

Figure 6

Evolution with surface velocity of the double isotope ratio temperature, T${}_{\mathrm{HHe}}$ for the two different reactions, 40 MeV/nucleon ${}^{40}\mathrm{Ar}$+${}^{112}\mathrm{Sn}$- and 55 MeV/nucleon ${}^{27}\mathrm{Al}$+${}^{124}\mathrm{Sn}$. Symbols of open circles, solid squares, open triangles, and solid circles correspond, respectively, to progressively increasing total neutron plus charged particle multiplicity. See text.

Figure 7

Interaction zone radii as a function of $V_{\mathrm{surf}}$. Values are presented for the four different ejectiles from the system 55 MeV/nucleon ${}^{27}\mathrm{Al}$+${}^{124}\mathrm{Sn}$. Symbols of open circles, solid squares, open triangles, and solid circles correspond, respectively, to data for ${}^2\mathrm{H}$, ${}^3\mathrm{H}$, ${}^3\mathrm{He}$, and ${}^4\mathrm{He}$, respectively. A similar trend is seen for 40 MeV/nucleon ${}^{40}\mathrm{Ar}$+${}^{112}\mathrm{Sn}$.

Figure 8

Interaction zone radii as a function of $V_{\mathrm{surf}}$. Values averaged over bins of 1 cm/ns in $V_{\mathrm{surf}}$ are presented for four different windows of total neutron plus charged particle multiplicity for the systems (a) 40 MeV/nucleon ${}^{40}\mathrm{Ar}$+${}^{112}\mathrm{Sn}$ and (b) 55 MeV/nucleon ${}^{27}\mathrm{Al}$+${}^{124}\mathrm{Sn}$. Symbols of open circles, solid squares, open triangles, and solid circles correspond, respectively, to progressively increasing total neutron plus charged particle multiplicity.

Figure 9

Emission zone radii vs. $A_{\mathrm{part}}^{\text{'}}$ (see text) for three different windows on $V_{\mathrm{surf}}$. Results for both reactions are presented as average values of $R_0$ for three bins of 1 cm/ns in $V_{\mathrm{surf}}$ in the range of 3 to 6 cm/ns. Average values of $V_{\mathrm{surf}}$ are (a) 5.5 cm/ns, (b) 4.5 cm/ns, and (c) 3.5 cm/ns. Symbols are as follows: solid triangles, 55 MeV/nucleon ${}^{27}\mathrm{Al}$+${}^{124}\mathrm{Sn}$, and solid squares, 40 MeV/nucleon ${}^{40}\mathrm{Ar}$+${}^{112}\mathrm{Sn}$. For comparison, the equivalent sharp cut-off radius for a normal density nucleus with $A=151$ is indicated by the open circles in each part of the figure.