Fe56(n,α)Cr<

Abstract

The energy and angular distribution of the a particles from the Fe(n, a) and Ni(n, o;} reactions for 14.1 MeV incident neutron energy were measured by means of a multitelescope system. The results concerning the total He-production cross sections and the angle-integrated u-emission cross sections der/dE are in fair agreement with previous measurements; for the angular distribution no detailed measurements have as yet been reported. The results are analyzed in the framework of the statistical model of nuclear reactions. Comparison of such calculations with the measured aemission cross sections allows one to extract nuclear level densities for ' Cr and Fe, the residual nuclei reached in the studied reactions in the energy region up to the neutron binding energy, and for Fe and Ni, the residual nuclei reached by neutron emission for energies around 11 MeV. Within experimental error a purely exponential increase of the level density with excitation energy was found for both ' Cr and Fe. The spin cutoff parameters for ' Cr and Fe derived from the data indicate that there is no reduction of the effective moment of inertia below the rigid body value.

Fast-neutron induced pre-equilibrium reactions on 55Mn and 63,65Cu at energies up to 40 MeV

“…The same effect is seen in the case of the target nucleus 55 Mn, for which the experimental α-particle spectra [63,64] are given as function of channel energy and no further conversion is necessary for comparison with the model calculation. This underestimation was noted as well for other target nuclei in this mass region [65,66], indicating that there may be considerable direct excitation of residual nuclei low lying levels beyond the validity of the PE models.…”

“…[48] are given in the laboratory system, their conversion to the center-of-mass system is equivalent to a shift of the spectrum to higher energies, of up to one MeV for the most energetic α-particles (see, e.g., Refs. [65,66]). Thus a good agreement is seen between the measured and calculated α-particle emission spectra for 63,65 Cu nuclei, apart from considerably higher measured data for the high energy parts of the spectra corresponding to excitations below ∼2 MeV in the residual nuclei 60,62 Co.…”

“…Concerning the additional underestimation of the α-particle spectrum on 55 Mn at lowest energies, one should note that the measurements are complicated in this energy range by a rather large background [66].…”

An update on (n,charged particle) research at WNR

“…helium production cross sections near 10 and 15 MeV,14,15 and with charged-particleemission measurements. [16][17][18][19] As found in the 58Ni case, the ENDF/B-VI evaluation for 6%i overestimates the cross section from threshold to about 14 MeV where it was constrained by measured values. The disagreement with our data can be as large as 75%.…”

Nuclear level densities below 40 MeV excitation energy in the mass regionA ≃ 50

“…The analysis of the proton and c~-particle emission spectra (Figs. 4, 5) reveals also a good description of the statistical as well as pre-equilibrium processes (there are contributions from direct reactions at the highest czparticle energies [43,44], not taken into account). This conclusion is quite important for the goals of the present work, the single-particle level density given by (2) and (4) significantly determining the preequilibrium emission cross section.…”