Level density and spin cutoff parameters from continuum (p,n) and (α,n) spectra

Neutron spectra produced by ($p,n$) reactions on ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ti}$, ${}_{}{}^{49}{}_{}{}^{}\mathrm{Ti}$, ${}_{}{}^{55}{}_{}{}^{}\mathrm{Mn}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Fe}$, and ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ and ($\alpha ,n$) reactions on ${}_{}{}^{45}{}_{}{}^{}\mathrm{Sc}$, ${}_{}{}^{49}{}_{}{}^{}\mathrm{Ti}$, ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$, ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$, and ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$ have been measured at four bombarding energies. The component of the spectra corresponding to equilibrium (evaporation) processes was identified from the angular and bombarding energy dependence of the continuum cross sections. Level density parameters $a$ were deduced from the shape of the equilibrium emission spectra and spin cutoff parameters $\sigma$ were obtained from the anistropy of the ($\alpha ,n$) angular distributions. Theoretical values for $a$ and $\sigma$ were obtained from a thermodynamic calculation with realistic single particle levels; these agreed well with the measured values. In particular, the mass number $A$ dependence of $\sigma$ was reproduced by the calculation and results from the variation with $A$ of angular momentum values of single particle levels near the Fermi level.