Search for temperature and $N∕Z$ dependent effects in the decay of $A=98$ compound nuclei

Fusion-evaporation reactions induced by $110\text{MeV}$ ${}^{11}\mathrm{B}$ and radioactive ${}^{11}\mathrm{C}$ on ${}^{87}\mathrm{Rb}$ targets have been studied by measuring evaporation residue–light particle coincidences. The proton to $\alpha$ particle ratio in each reaction has been derived and compared with predictions from statistical model calculations. These calculations account rather well for the experimental data, when a small empirical adjustment of the emission barrier is performed, in agreement with earlier results. No evidence is found for predicted temperature and isospin modification of the binding energies. The possibility of a further study of isospin and temperature dependent effects in fusion-evaporation reactions with radioactive beams is discussed.

Figure 1

(Color online) Expanded view of the experimental setup. The SI-BARREL elements are single detectors ($300\mu \mathrm{m}$ thickness, $5\times 5{\text{cm}}^2$ area) indicated as B1–B6. The two telescopes S1-M1 and S2-M2 are made of a transmission ($300\mu \mathrm{m}$ thick) detector backed by a $1\text{mm}$ thick detector. The area of the telescope detectors is $6\times 4{\text{cm}}^2$. The two evaporation residue trigger detectors are indicated as SI1 and SI2 and are also $300\mu \mathrm{m}$ thick with a $25{\text{cm}}^2$ area.

Figure 2

(Color online) A typical time-of-flight vs energy scatter plot for the reaction products from the bombardment of the ${}^{11}\mathrm{C}$ beam on the RbCl(C) target. The expected regions for residues from the different target nuclei are also indicated. In the inset, the region of evaporation residues from the reaction on the Rb target is shown. Events at about $E=6\text{MeV}$, randomly distributed in time, are due to a weak ${}^{252}\mathrm{Cf}$ source that was used to monitor the silicon triggers during the data taking.

Figure 3

(Color online) Typical ER energy spectra obtained for the residue-charged particle coincidence for the ${}^{11}\mathrm{B}$ beam (upper part) and the ${}^{11}\mathrm{C}$ beam (lower part) detected in the backward part of the SI-BARREL for a TOF window corresponding to $30–60\text{ns}$ flight time.

Figure 4

(Color online) Spectra of the charged particles in coincidence with the ER for the $110\text{MeV}$ for the ${}^{11}\mathrm{B}$ beam (upper part) and the ${}^{11}\mathrm{C}$ beam (lower part) on a ${}^{87}\mathrm{Rb}$ target.

Figure 5

Typical time-of-flight neutron spectra in coincidence with the ER for the $110\text{MeV}$ ${}^{11}\mathrm{B}$ beam (upper part) and the ${}^{11}\mathrm{C}$ beam (lower part) on a ${}^{87}\mathrm{Rb}$ target, with (dashed area) and without the suppression of the $\gamma$ background operated by means of the pulse shape analysis.

Figure 6

(Color online) Comparison of experimental result for the proton to $\alpha$ particle ratio and predictions from statistical model calculations with different level density parameters. The relative deviation $\Delta$ is reported. For details see the text.

Figure 7

(Color online) Comparison of experimental result for the proton to $\alpha$ particle ratio and predictions from statistical model calculations with different transmission coefficients. The relative deviation $\Delta$ is reported. For details see the text.