55Mn(

Abstract

The energy and angular distributions of the \ensuremath{\alpha} particles from the $^{55}\mathrm{Mn}$(n,x\ensuremath{\alpha}) and $^{59}\mathrm{Co}$(n,x\ensuremath{\alpha}) reactions for 14.1 MeV incident neutrons were measured by means of a multitelescope system. The results concerning total helium production are in good agreement with existing helium accumulation measurements, whereas the angular distributions reported in the literature for the $^{59}\mathrm{Co}$(n,\ensuremath{\alpha}) reaction could not be confirmed. The results are analyzed in the framework of the statistical model of nuclear reactions. Comparison of such calculations with the measured \ensuremath{\alpha}-emission cross sections allows the extraction of nuclear level densities for $^{52}\mathrm{V}$ and $^{56}\mathrm{Mn}$, the residual nuclei reached in the reactions studied, in the energy region up to the neutron binding energy, and for $^{55}\mathrm{Mn}$ and $^{59}\mathrm{Co}$, the residual nuclei reached by neutron emission, for energies around 11 MeV. The level densities derived in this way agree very well with the prediction of the back-shifted Fermi-gas model for the level density parameters of Strohmaier and Uhl. For $^{52}\mathrm{V}$ and $^{56}\mathrm{Mn}$ there is also excellent agreement with the level densities derived from average s-wave neutron resonances. The spin cutoff factors derived from the \ensuremath{\alpha}-particle angular distributions indicate that there is no reduction of the effective moment of inertia below the rigid body value.