Preequilibrium neutron emission from O + Al at 7.5 MeV/nucleon and 8.8 MeV/nucleon

The thick target neutron yield from a ${}^{16}{\mathrm{O}}^{6+}$ beam on a thick ${}^{27}\mathrm{Al}$ target at 120- and 142-MeV (7.5- and 8.8-MeV/nucleon, respectively) incident energies is presented and compared with theoretical calculations. The theoretical estimates for the yield of a high-energy neutron was obtained using a preequilibrium (PEQ) heavy-ion reaction model (hion), whereas that for the low-energy part was obtained using the standard evaporation models pace4 and empire 3.2. In the present data a significant PEQ contribution, $\sim 2\%$ to 3% of the evaporation contribution, is observed even at projectile energies below 10 MeV/nucleon. The measured energy spectrum of neutrons for $E>20\mathrm{MeV}$ (the predominant PEQ region) is in good agreement with the PEQ model code hion.

Figure 1

The experimental setup for the ${}^{16}\mathrm{O}+{}^{27}\mathrm{Al}$ system. (a) Schematic arrangement and (b) simplified block diagram of the electronic setup for the signal acquisition.

Figure 2

A typical experimental output of the $n$-γ separation (a) pulse height and PSD spectra and (b) contour plot of PSD and TOF spectra for the ${}^{16}\mathrm{O}+{}^{27}\mathrm{Al}$ system.

Figure 3

A comparison between the experimental neutron yield at 120 and 142 MeV.

Figure 4

Comparison of the experimental neutron yield with evaporation estimates from the statistical model codes pace and empire at (a) 120 MeV and (b) 142 MeV, respectively. The spectra for $0^{\circ },{30}^{\circ },{60}^{\circ },{90}^{\circ }$, and ${120}^{\circ }$ are multiplied with ${10}^n$ with $n$ being 4, 3, 2, 1, and 0, respectively.

Figure 5

Nucleon density distribution for the compound nucleus ${}^{43}\mathrm{Sc}{(}^{16}\mathrm{O}{+}^{27}\mathrm{Al})$ system using (a) the semiphenomenological and (b) the RMF approaches.

Figure 6

Comparison of experimental neutron yield with hion estimated PEQ contribution at (a) 120 MeV and (b) 142 MeV.

Figure 7

Comparison of the evaporation subtracted experimental spectra with hion estimates at (a) 120 MeV and (b) 142 MeV.