J. D. Pinheiro Filho

Nuclear fission of197Au,natPb and209Bi induced by polarized and monochromatic photons of 60 and 64 MeV

SummaryIn this paper we report experimental results on the fission cross-section and the fissionability of the197Au,natPb and209Bi nuclei at photons energies 60 and 64 MeV. The fissionability results agree satisfactorily with our estimate based on the statistical model and considerations on the mechanisms of nuclear disexcitation.RiassuntoSono riportati i risultati sperimentali sulla sezione d’urto di fissione e sulla fissionabilità dei nuclei di197Au,natPb e209Bi indotte dai fotoni monocromatici e polarizzati del fascio LADON dei Laboratori Nazionali di Frascati alle energie medie di 60 e 64 MeV. I risultati sulla fissionabilità sono in soddisfacente accordo con una stima che abbiamo ottenuto tenendo conto del modello statistico e di altre considerazioni sui meccanismi di diseccitazione nucleare.РезюмеВ этой статье мы приводим эспериментальные результаты по измерению поперечного сечения деления и расщепляемости ядер197Au,ectPb и209Bi фотонами с энергиями 60 и 64 МэВ. Результа.ы для расщепляемости удовлетворительно согласуются с оценками, основанными на статистической модели и на рассмотрении механизмов девозбуждения ядер.

Evaluation of Total Nuclear Photoabsorption Cross-Sections by the Modified Quasi-Deuteron Model

Levingers modified quasi-deuteron model has been used to analyse available experimental data on total nuclear photoabsorption cross-section in the mass range 7 ≤ A ≤ 238 and in the energy range (35 ÷ 140) MeV. It is shown that the measured cross-sections are successfully reproduced by the formula σT(Eγ) = LNZ/AσD(Eγ) exp [- D/E] with L = 6.1 ± 2.2 and D = 0.72A0.81.

Thermal annealing of proton tracks with energies of 4 and 6 MeV in Cr-39 polymer detectors

Abstract In this paper, we study the thermal annealing of proton tracks of 4 and 6 MeV at temperatures ranging from 150 to 240°C in CR-39 polymer detectors. A special experimental set-up for irradiating the detectors was arranged to obtain adequate proton beams from the Cyclotron CV-28 at IPEN/SP, Brazil. We report experimental data on track densities, track diameters, and activation energies based on current annealing models for the annealing of proton tracks in the energy range investigated. A value of (0.20±0.02)eV was determined as the mean activation energy of the annealing process in CR-39 detectors.

Cross sections of (γ, xn) reactions in complex nuclei at intermediate energies☆

Cross sections per equivalent quantum, in the energy range 0.3–1.0 GeV, have been measured for 209Bi(γ, 2n), 209Bi(γ, 3n), 209Bi(γ, 4n), 59Co(γ, 2n), 509Co(γ, 3n), 59Co(γ, 4n) and 51V(γ, 3n) reactions. From the calculated mean absolute cross sections and the data already available in literature for (γ, xn) reactions (x ≥ 1), a cross section formula has been deduced which reproduces, within a factor of two, most of the experimental cross sections for target nuclei ranging between 9Be and 238U.

Analysis of fission and fragmentation events produced in Ag and Br nuclei by interaction of bremsstrahlung beams in the energy range (1.0÷5.5) GeV

SummaryNuclear emulsion plates Ilford-K0 exposed to (1.0÷5.5) GeV bremsstrahlung beams in order to study photoinduced break-up of Ar, Br nuclei have been processed to produce visible fission tracks for track analysis with optical microscope. Track-length distributions, angular distributions and angular correlations of the produced fragments obtained at six end-point bremsstrahlung energies are presented and discussed. The analysis of the data shows that the recorded events are produced by two different reaction mechanisms, namely fission and fragmentation. The absolute mean cross-sections per photon for fragmentation, binary and ternay fission of Ag, Br targets in the energy range investigated have been measured. Absolute mean cross-sections per photon and corresponding fissilities have been evaluated for binary fission of Ag and Br and compared with literature data.