Final Scientific EFNUDAT Workshop

Experimental Study of Energy Dependence of Proton Induced Fission Cross Sections for Heavy Nuclei in the Energy Range 200-1000 MeV.

Not scheduled

25m

Globe (CERN)

Speaker

Larisa Vayshnene (Petersburg Nuclear Physics Institute)

Description

The need for information concerning fission reactions induced in heavy nuclei by intermediate energy projectiles (a main channel of decay of heavy nuclei) has been obvious for a long time. The interest in this process emerges from both fundamental and applied problems of nuclear physics. In spite of extensive experimental efforts, the fission process of nuclei induced by intermediate energy projectiles remains insufficiently understood in many aspects. The measurements of the energy dependence of total fission cross sections of heavy nuclei induced by intermediate energy protons may add to our understanding of the fission process in terms of nuclear properties of highly excited nuclei, such as temperature dependence of level density and fission barriers of excited nuclei. For physics applications the nuclear data are required for new energy production concepts with the help of accelerator driven systems (ADS), for nuclear waste transmutation technologies, for accelerator and cosmic device radiation shields as well as for applications in medicine and solid state investigations. Moreover, total fission cross section values are needed for the creation of monitoring standards for moderate energy proton beams. All the above mentioned problems require fission cross section data with high accuracy and reliability. The results of the total fission cross sections measurements for natPb, 209Bi, 232Th, 233U, 235U, 238U, 237Np and 239Pu nuclei at the energy proton range 200-1000 MeV with step 100 MeV are presented. Experiments were carried out at 1 GeV synchrocyclotron of PNPI with the updated beam system that allows one to have proton beams with intensity up to 107 protons/s in all energy range. The measurement method is based on the registration in coincidence of both complementary fission fragments by two gas parallel plate avalanche counters, located at a short distance and opposite sides of investigated target. The insensitivity of parallel plate avalanche counters allowed us to place the counters together with target between immediately in the proton beam thereby providing a large solid angle acceptance for fission fragment registration and reliable identification of fission events. The proton flux on the target to be studied was determined by direct counting of protons by scintillation telescope and using secondary reaction of elastic proton scattering by CH2 target. Obtained results are compared with other experimental data and show that the fission cross sections do not depend strongly on the incident proton energy over this entire energy range.