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JLab APS Centennial Presentations | ||||
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Photofission of Heavy Nuclei at Intermediate Energies Session OB12 - Photoproduction and Electroproduction of Mesons. ORAL session, Wednesday morning, March 24 Room 219E, GWCC C. Cetina, B.L. Berman, W.J. Briscoe, G. Feldman, L.Y. Murphy, J.C. Sanabria (George Washington Univ.), H.L. Crannell, A. Longhi, D.I. Sober (Catholic Univ.), S.P. Barrow (Florida State Univ.), G.YA. Kezerashvili (Budker Inst.), V. Nederezov (Inst. for Nucl. Research, Russian Academy of Sciences), Jefferson Lab Photon Tagger Collaboration
The photofission probability of the uranium and transuranic
isotopes has been assumed for many years to be approximately equal to
unity for E_\gamma > 50 MeV.
Recent experiments, including our previous measurements at SAL,
contradict this assumption, indicating that the fission probability for
neptunium is higher than that for the uranium isotopes.
We now have performed a simultaneous measurement of the photofission cross
sections for ^238U, ^235U, ^233U,
^237Np, ^232Th, and ^NATPb using tagged photons of energy
E_\gamma=0.17-3.84 GeV.
This was the first experiment to use the Photon Tagging Facility
of Hall B at Jefferson Lab.
The parallel-plate avalanche fission-fragment detectors
were designed and built at GW.
Preliminary results confirm that the cross section for ^238U relative
to that for ^237Np is about 80%,
implying the presence of important competing processes other than fission.
Also, the fission probability as a function of incident photon energy
is almost constant, with the saturation value depending on the fissility
parameter Z^2/A.
Final results will include absolute photofission cross
sections for all six nuclei.
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