Photofission Cross Sections ofU235,U238,

J.A. Jungerman

¹

,

H. Steiner²

Abstract

The angle 6 is the polar angle of the nucleon relative momentum with respect to the incident-proton direction in the total center-of-mass system. The angles 6± and 02 are the polar angles of the two mesons with respect to this direction, also in the total center-of-mass system, if one neglects the transformation from the rest system of each isobar. By integration over the meson angles in Eqs. (3) and (4), we can get an idea of the angular distribution of the final-state nucleons that could arise from inclusion of the P-wave motion of the intermediate-state isobars. For the transition from the 3 Po state, we have S EVERAL experiments have been performed to investigate photofission cross sections in the energy region 100 to 300 Mev. 1-5 In the experiment here presented we have investigated the photofission cross sections of U 238 , U 235 , Th 232 , Bi 209 , and Au 197 for photons produced in bremsstrahlung spectra whose maximum energies ranged from 150 to 500 Mev. The energy region 150 to 335 Mev was investigated for the most part at the University of California synchrotron, whereas the higher energy data were obtained at the synchrotron of the California Institute of Technology. In a previous paper 6 (hereafter referred to as A) we have reported the high-energy proton-induced fission cross sections of the above elements. The same apparatus and essentially the same methods were used in the measurement of the photofission cross sections.

Product yields for the photo-fission of 209Bi with 2.5 GeV bremsstrahlung

“…2. The FWHM of the mass-yield distribution increases from 19 mass units at [28][29][30][31][32][33][34][35][36][37][38][39][40] MeV to 51 mass units at 2.5 GeV bremsstrahlung-induced fission of 209 Bi. On the other hand the average mass of the mass-yield distribution decreases from 103 ± 0.5 at 28-40 MeV to 95 ± 0.5 at 2.5 GeV.…”

“…It is well known that the mass-yield distribution in the charged particle-induced fission of pre-actinides [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] such as Ra is asymmetric with three humps [19], whereas that for Bi, Pb, and Au, becomes symmetric. Even the mass-yield distribution of Au, Pb, and Bi in the bremsstrahlung-induced fission is symmetric [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50]. This indicates that the mass-yield distributions for both charged particle-and bremsstrahlung-induced fission of Au, Pb, and Bi are symmetric.…”

“…This indicates that the mass-yield distributions for both charged particle-and bremsstrahlung-induced fission of Au, Pb, and Bi are symmetric. It has been also observed that the full width at half maximum (FWHM) of the mass-yield distribution in the charged particle-induced fission of 209 Bi [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] increases from 17 mass units for [15][16][17][18][19][20][21][22] MeV deuteron-induced fission [25] to 24 mass units for the [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] MeV helium-induced fission [19][20][21]. The FWHM of the mass-yield...…”

“…The mass-yield distribution for charged particle-induced fission in the incident energy between 450 MeV and 2.2 GeV flattens through the fission fragment region and the spallation becomes the dominant reaction [29]. The FWHM of the mass-yield distribution in the bremsstrahlunginduced fission of 209 Bi also increases from 19 mass units at [28][29][30][31][32][33][34][35][36][37][38][39][40] to 23 mass units at 85 MeV [31,32]. However, the FWHM of the mass-yield distribution in the bremsstrahlung-induced fission of 209 Bi [31,32] does not increase so sharply with energy compared to the case of the charge particle-induced fission [19][20][21][22][23][24][25][26][27][28][29][30].…”

Photofission of209Bi at intermediate energies

“…The total photofission yields and/or cross sections on 209 Bi have been extensively measured with ionization chambers and solid-state track detectors so far [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. However, a few works measuring charge distribution and/or mass yield distribution, which are further essential for understanding of fission mechanisms, were performed in the past [34][35][36][37].…”