Transfer- and fusion-induced fission in inverse kinematics has proved to be a powerful tool to investigate nuclear fission, widening information on the fission fragments and access to unstable ...fissioning systems with respect to other experimental approaches. An experimental campaign is being carried out at GANIL with this technique since 2008. In these experiments, a beam of U-238, accelerated to 6.1 MeV/u, impinges on a C-12 target. Fissioning systems from U to Cf are populated through inelastic scattering, transfer, and fusion reactions, with excitation energies that range from a few MeV up to 46 MeV. The use of inverse kinematics, the SPIDER telescope, and the VAMOS spectrometer allow the characterization of the fissioning system in terms of mass, nuclear charge, and excitation energy, and the isotopic identification of the full fragment distribution. This work reports on new data from the second experiment of the campaign on fission-fragment yields of the heavy actinides U-238, Np-239, Pu-240, Cm-244, and Cf-250, which are of interest from both fundamental and application points of view.
The energy loss of heavy ions in thin Mylar and nickel foils was measured accurately using fission fragments from 239Pu(nth,f), mass and energy separated by the Lohengrin separator at ILL. The ...detection setup, placed at the focal plane of the Lohengrin separator enabled to measure precisely the kinetic energy difference of selected fragments after passing through the sample. From these data, the stopping powers in Mylar and nickel layers were extracted and compared to calculations. Whereas large deviations are observed with SRIM-2013 for Mylar, fairly good agreements are obtained with the semi-empirical approach of Knyazheva et al. (2006) and the calculations contained within the DPASS database. In nickel, SRIM-2013 and Knyazheva model are in agreement with our data within about 10%, while large deviations are observed with DPASS. We used our data to provide updated parameters for the Knyazheva model and rescale DPASS database for nickel and Mylar.
The use of the inverse kinematics technique and a magnetic spectrometer permits the simultaneous measurement of proton and neutron content of full fission fragment distributions. This paper reports ...new measurements of five fissioning systems—U238,Np239,Pu240,Cm244, and Cf250—produced in inelastic scattering, transfer, and fusion reactions at different excitation energies. As a result, isotopic, elemental, and isotonic fission yields are presented. The contribution of the different fission modes and the proton even-odd effect are studied. Structure effects are investigated by means of the neutron excess and the total neutron multiplicity as a function of the fragment atomic number.
Nuclear fission is still one of the most complex physical processes we can observe in nature due to the interplay of macroscopic and microscopic nuclear properties that decide the result. An example ...of this coupling is the presence of nuclear dissipation as an important ingredient that contributes to drive the dynamics and has a clear impact on the time of the process. However, different theoretical interpretations, and scarce experimental data make it poorly understood. In this Letter, we present the first experimental determination of the dissipation energy in fission as a function of the fragment split, for three different fissioning systems. The amount of dissipation was obtained through the measurement of the relative production of fragments with even and odd atomic numbers with respect to different initial fission energies. The results reveal a clear effect of particular nuclear shells on the dissipation and fission dynamics. In addition, the relative production of fragments with even and odd atomic numbers appears as a potential contributor to the long-standing problem of the time scale in fission.
The neutrons for science (NFS) facility is a component of SPIRAL-2, the new superconducting linear accelerator built at GANIL in Caen (France). The proton and deuteron beams delivered by the ...accelerator will allow producing intense neutron fields in the 100 keV-40 MeV energy range. Continuous and quasi-mono-kinetic energy spectra, respectively, will be available at NFS, produced by the interaction of a deuteron beam on a thick Be converter and by the 7Li(p,n) reaction on thin converter. The pulsed neutron beam, with a flux up to two orders of magnitude higher than those of other existing time-of-flight facilities, will open new opportunities of experiments in fundamental research as well as in nuclear data measurements. In addition to the neutron beam, irradiation stations for neutron-, proton- and deuteron-induced reactions will be available for cross-sections measurements and for the irradiation of electronic devices or biological cells. NFS, whose first experiment is foreseen in 2018, will be a very powerful tool for physics, fundamental research as well as applications like the transmutation of nuclear waste, design of future fission and fusion reactors, nuclear medicine or test and development of new detectors.
The study of nuclear fission is encountering renewed interest with the development of GEN-IV reactor concepts, mostly working in the neutron fast energy domain. To support the fast reactor ...technologies, new high quality nuclear data are needed. New facilities are being constructed to produce high intensity neutron beams from hundreds of keV to few tens of MeV (Licorne, NFS, nELBE, ...). They will open new opportunities to provide nuclear data. In this framework the development of an experimental setup called FALSTAFF for a characterisation of actinide fission fragments has been undertaken. Fission fragment yields and associated neutron multiplicities will be measured as a function of the neutron energy. Based on time-of-flight and residual energy technique, the setup will allow the simultaneous measurement of the complementary fragment velocity and energy. The FALSTAFF setup and the upgrade of the first arm prototype with the new ionisation chamber CALIBER will be presented. The performances of the experimental apparatus is discussed.
Experimental access to full isotopic fragment distributions is very important to determine the features of the fission process. However, the isotopic identification of fission fragments has been, in ...the past, partial and scarce. A solution based on the use of inverse kinematics to study transfer-induced fission of exotic actinides was carried out at GANIL, resulting in the first experiment accessing the full identification of a collection of fissioning systems and their corresponding fission fragment distribution. In these experiments, a 238U beam at 6.14 AMeV impinged on a carbon target to produce fissioning systems from U to Am by transfer reactions, and Cf by fusion reactions. Isotopic fission yields of 250Cf, 244Cm, 240Pu, 239Np and 238U are presented in this work. With this information, the average number of neutrons as a function of the atomic number of the fragments is calculated, which reflects the impact of nuclear structure around Z=50, N=80 on the production of fission fragments. The characteristics of the Super Long, Standard I, Standard II, and Standard III fission channels were extracted from fits of the fragment yields for different ranges of excitation energy. The position and contribution of the fission channels as function of excitation energy are presented.
In the past years, the fission studies have been mainly focused on thermal fission because most of the current nuclear reactors work in this energy domain. With the development of GEN-IV reactor ...concepts, mainly working in the fast energy domain, new nuclear data are needed. The FALSTAFF spectrometer under development at CEA-Saclay, France, is a two-arm spectrometer which will provide mass yields before (2V method) and after (EV method) neutron evaporation and consequently will have access to the neutron multiplicity as a function of mass. The axial ionization chamber, in addition to the kinetic energy value, will measure the energy loss profile of the fragment along its track. This energy loss profile will give information about the fragment nuclear charge. This paper will focus on recent developments on the FALSTAFF design. A special attention will be paid to the impact of the detector material thickness on the uncertainty of different observables.
Transfer- and fusion-induced fission in inverse kinematics was proven to be a powerful tool to investigate nuclear fission, widening the information of the fission fragments and the access to ...unstable fissioning systems with respect to other experimental approaches. An experimental campaign for fission investigation has being carried out at GANIL with this technique since 2008. In these experiments, a beam of 238U, accelerated to 6.1 MeV/u, impinges on a 12C target. Fissioning systems from U to Cf are populated through transfer and fusion reactions, with excitation energies that range from few MeV up to 46 MeV. The use of inverse kinematics, the SPIDER telescope, and the VAMOS spectrometer permitted the characterization of the fissioning system in terms of mass, nuclear charge, and excitation energy, and the isotopic identification of the full fragment distribution. The neutron excess, the total neutron multiplicity, and the even-odd staggering in the nuclear charge of fission fragments are presented as a function of the excitation energy of the fissioning system. Structure effects are observed at Z∼50 and Z∼55, where their impact evolves with the excitation energy.
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