Level widths and level densities inSi28,Ti46

Abstract

Ericson fluctuations in the differential cross sections were investigated for the compound reactions 27 Al͑p , n 0 ͒ 27 Si, 45 Sc͑p , n 4 ͒ 45 Ti, 45 Sc͑p , n 5 ͒ 45 Ti, 51 V͑p , n 0 ͒ 51 Cr, and 59 Co͑p , n 0 ͒ 59 Ni. Level widths in the compound nuclei 28 Si, 46 Ti, 52 Cr, and 60 Ni were extracted from the analysis of the differential cross sections by the Fourier method and a nonlinear fit to the ln͗A k 2 + B k 2 ͘ distribution. The neutron spectra for each reaction were measured at least at three backward angles but the coherence width ͗⌫͘ did not show a strong angular dependence. Nuclear level densities for the above nuclei were extracted by relating the average level spacing D J to the average level width ⌫ J using the fluctuation theory. Reasonable agreements were found with other level densities and level density compilations based in the Fermi gas formalism of Al-Quraishi and Huang for 28 Si, 46 Ti, and 52 Cr but the comparison diverges for 60 Ni for which additional measurements are required in order to clarify the observed discrepancies. The level density parameters that best describe the data are a = 3.5 and ␦ = 4.0, U Ͻ 25 MeV, for 28 Si, a = 4.8 and ␦ = −0.3, U Ͻ 20 MeV, for 46 Ti, and a = 4.8 and ␦ = 0.3, U Ͻ 20 MeV, for 52 Cr.

Test of nuclear level density inputs for Hauser-Feshbach model calculations

“…The mass resolution was sufficient to resolve protons, deuterons, 3 H/ 3 He, and α-particles. Additionally, the neutron spectra from both the 58 Fe( 3 He, Xn) and the 59 Co(d, Xn) reactions have been measured by the time-of-flight method with the Swinger facility of Edwards Laboratory [17]. Here a flight path of 7 m has been used to obtain better energy resolution for outgoing neutrons, allowing us to measure the shape of neutron evaporation spectrum more accurately.…”

“…Alpha-particle potentials are more uncertain. Differences between corresponding α-transmission coefficients depends on the α-energy and varies from ∼ 40% for lower α-energies to < 1% for higher α-energies in our region of interest (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). In order to reduce these uncertainties the RIPL α-potentials have been tested against the experimental data on low energy α−elastic scattering on 58 Ni [20].…”

Level density ofFe56and low-energy enhancement of γ-strength function

“…To measure the neutron spectrum, the beam swinger facility [10] has been used. This allows the measurement of angular distributions by rotating the incoming beam and the target chamber with respect to the direction of outgoing neutrons.…”

Fermi’s golden rule applied to theγdecay in the quasicontinuum ofTi46

“…However, the values reported by the various experimental groups differ within a factor of ten. The measurement of the Ohio group [18] is shown in Fig. 5 for comparison (see triangle point at 15.5 MeV).…”

“…Level densities in the 14 − 19 MeV excitation region of 46 Ti have been measured from Ericson fluctuations, see Ref. [18] and references therein. However, the values reported by the various experimental groups differ within a factor of ten.…”