Deep subbarrier anomalies in the photofission of heavy nuclei

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

“…We show in Fig. 2 Bremsstrahlung photon beams [12] and photons produced by positron annihilation in flight [16]. Good overall agreement is verified in the whole energy interval.…”

“…(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.…”

“…(ii) A wide structure ( W ≈ 0.4 MeV) around 5.7-5.8 MeV has been systematically observed in the photofission cross section [10,12].…”

“…(iii) such "unexpected" experimental finding for 237 Np has been tentatively attributed either to the fission process itself [12,13] or to the photonuclear process [10].…”

“…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).…”