Absolute photofission cross sections of 235,238U measured with tagged photons between 40 and 105 MeV

Photofission of235U and238U at intermediate energies: absolute cross sections and fragment mass distributions

“…8 with our previous data obtained at the tagging facility of the now dismantled 500 MeV synchroton of Bonn University [12]. In these experiments, due to the moderate photon flux, multiple parallel plate avalanche counters [5,33,32] with large total target surface densities of about 191 mg/cm 2 and 62 mg/cm 2 ( 238U and 235U, respectively) had to be used (compared with ~ 0.26 and 0.15 mg/cm 2 in the present experiments). In the figure only statistical errors are plotted.…”

“…The detector arrangement and associated CAMAC interface electronics were operated using the data acquisition system MECDAS [31]. The advantages of this system in comparison with the performances of the multiple PPAC detectors (~ 30 thick targets) [33,34] used in our previous photofission experiments [5,12,32] and which have subsequently been utilized in the recent Frascati measurements, [21,35] should be emphasized: angle covered by the detector arrangement for threefold and fourfold coincidences cannot be calculated analytically. Therefore, Monte Carlo simulations have been performed using the program GEANT [36].…”

“…The efficiency of the 47r detector device can be determined on line during the experiments in contrast to the multiple layer PPAC's [5,33,34] with thick targets, where special calibration runs using a thin target arrangement and increased bremsstrahlung intensities have to be performed (see [5,33,32]). This is not necessary for the present set up since only one thin target is used.…”

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

“…The first quantity is evaluated from Levinger's modified quasi-deuteron model [28], according to which (2) where a d (k) is the total photodisintegration cross section of the free deuteron, NZ is the number of neutron-proton pairs in the nucleus, and L and D are, respectively, the so-called "Levinger's" and "damping" parameters, both depending on mass number A. A systematic study by Terranova et al [29] of total nuclear photoabsorption cross section data taken in the range 35-140 MeV has shown that parameter D can be evaluated by D = 0.72 A ~ MeV, while from a very recent re-evaluation of Levinger's constant of nuclei throughout the Periodic Table by Tavares and Terranova [30] values of L have been calculated by L = 6.8-11.2 A -2/3 --5.7 A -4/3.…”

“…The use of monochromatic photon beams of energy greater than 20 MeV or so to study photonuclear reactions has produced in the last twelve years a number of reliable data on photoreactions, particularly those concerned with fission reactions (photofission) of actinide nuclei [1][2][3][4][5][6][7][8][9] and, to a lesser extent, of heavy-metal nuclei of mass number A < 210 [8,[10][11][12][13][14]. For incident photon energies in the range ,-~ 30-140 MeV, the photo fission data have been generally interpreted on the basis of a model which considers the primary nuclear photoabsorption as taking place between the incoming photon and a neutronproton pair (quasi-deuteron photoabsorption mechanism first proposed by Levinger [15]) followed by a process of competition between nucleon evaporation and fission experienced by the excited residual nucleus [5, 8, 9, 12-14, 16, 17].…”