Correlations between the alpha particles and ejectiles in the reactionNb93+N14atElab=208MeV

Abstract

The correlations between alpha particles and various ejectiles were investigated in the reaction $^{93}\mathrm{Nb}$+ $^{14}\mathrm{N}$ at ${E}_{\mathrm{lab}}=208$ MeV. The ejectiles were measured at a fixed angle ${\ensuremath{\theta}}_{1}=+22\ifmmode^\circ\else\textdegree\fi{}$, which was slightly more backward than the grazing angle, and the alpha particles were measured at various angles ${\ensuremath{\theta}}_{2}$ in and out of the reaction plane. The experimental results were analyzed in terms of various aspects of the correlations such as the energy and angular correlations, the projected energy spectra, and differential multiplicities. An analysis based on the three body kinematics was also made to study the features associated with the sequential ejectile breakup process. It was found that two processes contribute to the coincident alpha particles. The first process was ascribed to the sequential breakup of the excited ejectiles and was found to be dominant in the angular region of ${\ensuremath{\theta}}_{2}$ close to the ejectile detector. The coincidence cross section of the sequential breakup component can be approximately factorized as a product of the singles cross section of excited ejectiles before breakup and the excitation spectrum of the ejectiles. The other process, ascribed to a nonsequential mechanism, was dominant for the alpha particles detected on the opposite side of the ejectile detector with respect to the beam direction. This process is characterized by the following properties: (i) The energy spectra of the coincident alpha particles have shapes which are almost identical to those of the singles spectra taken at the same angles. (ii) The same is true to a lesser extent for the ejectile spectra except for the higher-energy region. (iii) In this angular region of ${\ensuremath{\theta}}_{2}$ the differential coincidence cross section can be approximately expressed in the factorization form, $\frac{{d}^{4}\ensuremath{\sigma}}{d{\ensuremath{\Omega}}_{1}d{\ensuremath{\Omega}}_{2}d{E}_{1}d{E}_{2}}=K\ifmmode\cdot\else\textperiodcentered\fi{}(\frac{{d}^{2}\ensuremath{\sigma}}{d{\ensuremath{\Omega}}_{1}d{E}_{1}})(\frac{{d}^{2}\ensuremath{\sigma}}{d{\ensuremath{\Omega}}_{2}d{E}_{2}})$. The relative contribution of the two processes was found to be roughly comparable.NUCLEAR REACTIONS $^{93}\mathrm{Nb}$($^{14}\mathrm{N}$,$\mathrm{HI}\ensuremath{\alpha}$), $E=208$ MeV; measured two-dimensional HI-$\ensuremath{\alpha}$ coincident energy and angular correlations; deduced reaction mechanisms.