Elsevier

Nuclear Physics A

Volume 292, Issues 1–2, 21–28 November 1977, Pages 225-236
Nuclear Physics A

Fission fragment energy correlation measurements for the thermal neutron sub-barrier fission of 237Np and above-the-barrier fission of 235U

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Abstract

Fission fragment mass and kinetic energy distributions and mass-versus-energy correlations have been measured at the Grenoble high-flux reactor for the thermal neutron induced sub-barrier fission and above-the-barrier fission of 237Np and 235U, respectively. Unwanted events were eliminated by careful timing. In the case of 237Np(nth, f), the two odd particles (one proton and one neutron) are, on the average, shared out equally between the two complementary fragments leading to 〈μH〉, being 1 amu higher than the value for the neighbouring even-even fissioning nuclei. The peak mass yield for 237Np is 5.7 % compared to 6.5 % for 235U. The peak valley ratios of mass distribution are 124 and 544 for 237Np and 235U, respectively. The mass distribution for 237Np is wider than for 235U and broadens more towards more asymmetric fission than towards symmetric fission. The global mass distributions for 237Np and 235U show fine structures. For events with high total kinetic energy, the yield of mass around 136 seems to dominate for 237Np compared to mass 134 for 237U. The periods of the fine structures seem to be ≈ 2.5 amu and 5 amu for 237Np and 235U, respectively. The 〈EK〉 for 237Np is about 4 MeV less than the expected value. It is, respectively, ≈ 0, 5 and 1.5 MeV less for the mass regions μH≈ 119–124, 124–135, and 135 and beyond. It is shown that these results are qualitatively consistent with Nörenberg's model. However, it is shown that this model does not explain these results quantitatively.

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Nuclear Physics Laboratory, INW, B-9000 Gent, Belgium.

††

Department de Reserche Fondamentale, CEN-Grenoble, France.

†††

NFWO, INW B-9000 Gent and SCK/CEN B-2400 Mol, Belgium.

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