Absolute photofission cross sections for 232Th and 235,238U measured with monochromatic tagged photons (20 Mev < Eγ < 110 Mev)

Analysis of209Bi and238U photofission cross section in the quasi-deuteron region of photonuclear absorption

“…Most of the experimental cross section data is dispersed within the interval 10-20 mb, showing that the cross section is not well defined in the energy range 30-140 MeV. The measurements by Lepr~tre et al [5] (open circles) constitute the unique comprehensive set of data covering the region 40-105 MeV, these data being compatible with a constant Fig. 8 c); the full line is the result of the Monte Carlo calculation by Lepr~tre et al [5].…”

“…The significant de-excitation channels are neutron emission and fission, although a small contribution from proton and alpha-particle emission channels has been also considered at energies E*>80 MeV for 2~ target nucleus (in the case of 238U this contribution turns out inessential). In the present calculation not all sucessive chance fission probabilities have been included, but only the firstchance and the significant contribution due to the secondchance fission probability, in such a way that, starting from a certain residual nucleus Z* ( ; ,Aft,E*), i=1, 2, 3 as before, the total fission probability expected for such a nucleus is obtained by (5) (superscripts denote here the order of the chance fission.) Since for excitation energies up to 140 MeV neutron emission predominates strongly over proton and alpha-particle emissions, it was sufficient to consider for the second-chance fission a residual nucleus formed from its precedent by loosing of one neutron.…”

Fissility of actinide nuclei by 60-130 MeV photons

“…Hence, from Eqs. (2,3), and by making use of the experimental data of σ f for 237 Np (Table 1, 10 th column), the Pauli block function in the incident photon energy range 60-130 MeV, can be expressed as This result is shown in Fig.1-b (straight line) together with the semiempirical values of f B (circles). For a comparison, the results of a Monte Carlo calculation (full squares in Fig.1-b) obtained by de Pina et al [19] is also shown.…”

“…In particular, the development of highperformance parallel-plate avalanche detectors ( PPAD ) for fission fragments [2,5,9,10] has allowed researchers to obtain photofission cross section data for actinide target nuclei (Th, U, Np) within ∼ 5% of uncertainty, and for pre-actinide (Pb, Bi) within ∼ 12%, covering a large incident photon energy-range from about ∼30 MeV on.…”

“…The experimental data from such photonuclear reactions (cross section measurements and fission probability) have been generally interpreted on the basis of a current nuclear photoreaction model for intermediate-(30 E γ 140 MeV) and high-(E 140 MeV) energy photons [2,[11][12][13][14]. In brief, during the first reaction step, the incoming photon interacts with a neutron-proton pair (E γ 500 MeV) and/or individual nucleons (E γ 140 MeV), where pions and baryon resonances, and recoiling nucleons initiate a rapid (∼ 10 −23 s) intranuclear cascade process which produces a residual, excited nucleus.…”