Photonuclear cross sections of Pu-239 using neutron capture gamma rays, near threshold

Abstract

The photofission and photoneutron cross sections of Pu-239 have been measured by using monochromatic and discrete photons produced by thermal neutron capture gamma rays in several targets placed at the core of the IEA-R1 reactor in the energy interval from 5.43 MeV to 9.72 MeV. Analysing the photofission and photoneutron data we have observed similarities between the cross sections obtained for Pu-239 in comparison with the data obtained by other authors. From the photofission cross sections obtained and according to the liquid drop model, the height of the simple fission barrier was determined: F.E. = (5.7 f 0.2) MeV. The relative fissionability to U-238 was also determined and shown to be energy independent: F.R. = (3.32 & 0.41). For the competition between the photoneutron and the photofission emission (r/rf) a constant value was found: (0.44 & 0.05).By using this result the following nuclear temperature for Pu-239 was determined on basis of Nuclear Constant Temperature model of level density: T = (0.49 f 0.05) MeV. The total photoabsorption cross sections were calculated as well as the photofission branching ratio (Tf/TA), or fission probability Pf. A constant value was also found: Pf = (0.70 f 0.06).

Restricted spin-range correction in the Oslo method: The example of nuclear level density and γ -ray strength function from Pu239(d,pγ)Zeiser1, Tveten2, Potel3 et al. 2019Phys. Rev. C121801View full textAdd to dashboardCite

“…7, we compare the input γSF of the 3 rd iteration to the result of the initial analysis (see Sec. IV) and the measurements of Kopecky et al [55], De Moraes and Cesar [57] and Gurevich et al [58]. The absolute scale of the proposed γSF is lower than in the initial analysis, which is attributed to the increased NLD (see Fig.…”

“…There are no measurements for the Giant Dipole Resonance (GDR) of 240 Pu. However, as the GDR is expected to vary little between the plutonium isotopes, we also include 239 Pu(γ, abs) measurements (again included in Y sum ) by De Moraes and Cesar [57] and Gurevich et al [58]. A third dataset by Berman et al [59] is yield systematically lower crosssections than the first two measurements, which where consistent within the error-bars.…”

Breaking of axial symmetry in excited heavy nuclei as identified in giant dipole resonance data

“…19 favors our ansatz over the other models, especially when the strongly reduced number of fit parameters is regarded. [155] (black circles) and by discrete γ-rays from neutron capture [156](magenta stars on the low energy slope).…”

Monoenergetic photon-induced fission cross-section ratio measurements for U235 , U238 , and Krishichayan1, Finch2, Howell3 et al. 2018Phys. Rev. C

“…The energy spread in the measurement at each γ-ray beam energy was between 200 and 400 keV FWHM, which is not shown in the plots for consistency with the literature data to which we compare our data. Also shown in these figures are the ratios computed from the 235 U cross-section data of Bowman et al [17], Caldwell et al [15], Ries et al [18], and Soldatov et al [22]; the 238 U cross-section data of Katz et al [24], Bergere et al [26], Veyssière et al [14], Neto et al [28], Caldwell et al [15], Ries et al [18], and Soldatov et al [22]; and the 239 Pu cross-section data of Katz et al [24], Shapiro et al [21], Berman et al [16], Moraes et al [20], and Soldatov et al [22]. These previous data for 235 U, 238 U, and 239 Pu were interpolated/extrapolated to correspond to the incident photon energies used in the present work.…”

“…The photons were obtained by Compton scattering of γ rays produced by neutron capture on nickel. Similarly, Moraes et al [20] used thermal neutron capture γ rays in several targets placed at the core of a reactor to measure the photofission cross section of 239 Pu near the threshold region.…”