Photofission Cross Sections for²³⁷Np in the Energy Interval from 5.27 to 10.83 MeV

Role of transitional levels inNp237(γ,f): Perspectives for studying highly deformed systems

“…(i) In the first place, there are several works presenting calculations of fission barrier heights, using semimicroscopic models based on the Strutinsky [26][27][28] and Hartree-Fock [29,30] methods. However, absolute values for barrier heights from these theoretical approaches, are systematically lower than those obtained from the fitting of cross sections by means of statistical model calculations [11][12][13][14][15][16]23,24]. (ii) In the second place, and considering that the uncertainties associated with our measurements [15] are modest, we note that small differences between the selected barrier heights entering our model calculations could eventually destroy the agreement between level groups (and level voids) and the corresponding structures in the measured cross sections.…”

“…However, absolute values for barrier heights from these theoretical approaches, are systematically lower than those obtained from the fitting of cross sections by means of statistical model calculations [11][12][13][14][15][16]23,24]. (ii) In the second place, and considering that the uncertainties associated with our measurements [15] are modest, we note that small differences between the selected barrier heights entering our model calculations could eventually destroy the agreement between level groups (and level voids) and the corresponding structures in the measured cross sections. In fact, this drawback explains why theoretically obtained fission barriers are not generally used in statistical calculations of cross sections.…”

“…(vi) More recently, finally, a very high resolution crosssection measurement of 237 Np (γ,f ) revealed two structures at ∼5.7 and ∼6 MeV [15].…”

“…In fact, we measured the 237 Np photofission cross section in the energy interval 5.27-10.83 MeV, using γ -ray spectra produced by thermal neutron capture [15]. As shown in Fig.…”

“…Thus, our approach strongly depends on accurate calculations of single-particle states for very deformed shapes. In this regard, it is necessary to achieve σ γ, 237 Np measured by three different techniques: neutroncapture γ rays [15], Bremsstrahlung [12], positron annihilation in flight [16], and theoretically calculated photofission cross section (this work).…”