X-ray fluorescence from the element with atomic number Z = 120

Accepted for publication in Physical Review LettersAn atomic clock based on X-ray fluorescence yields has been used to estimate the mean characteristic time for fusion followed by fission in reactions 238U + 64Ni at 6.6 MeV/A. Inner shell vacancies are created during the collisions in the electronic structure of the possibly formed Z=120 compound nuclei. The filling of these vacancies accompanied by X-ray emission with energies characteristic of Z=120 can take place only if the atomic transitions occur before nuclear fission. Therefore, the X-ray yield characteristic of the united atom with 120 protons is strongly related to the fission time and to the vacancy lifetimes. K X-rays from the element with Z = 120 have been unambiguously identified from a coupled analysis of the involved nuclear reaction mechanisms and of the measured photon spectra. A minimum mean fission time $\tau$_f$ = 2.5×10−18s has been deduced for Z=120 from the measured X-ray multiplicity

Fluorescence X appliquée à l'étude du temps de fission de l'élément Z=120

Characteristic X-rays of the element Z=120 have been identified in the reaction 238U+64Ni at 6,6 MeV. They have been detected in coincidence with fission fragments arising from composite systems with 120 protons formed during the reaction. Pieces of information about the formation probability by fusion of Z=120 nuclei and on the fission time of this nucleus have been inferred from the X-ray multiplicity.L'étude de la réaction 238U + 64Ni 'a 6,6 MeV par nucléon nous a permis d'identifier des rayons X caractéristiques de l'élément Z = 120. Ces X caractéristiques ont été trouvés en coïncidence avec des fragments de fission des noyaux composés de 120 protons formés au cours de la réaction. La multiplicité de ces rayonnements rend possible l'extraction des informations sur la probabilité de formation par fusion dans la réaction étudiée du noyau de Z = 120 ainsi que sur le temps de fission de ce noyau

NFS Neutron beam characterization and monitoring

International audienc

Light response and efficiency calibration of EJ309 liquid scintillator between 3 and 45 MeV

International audienceThe Neutrons For Science (NFS) facility will provide intense neutron beams in the energy range between 1 MeV and 40 MeV. The neutron monitoring will be ensured by a detector consisting of a glass cell containing EJ309 liquid scintillator coupled to a photomultiplier. The goal of this study was the characterization of this monitor. Two experiments were performed to measure the light response of the scintillator from 3.6 MeV to 45 MeV as well as the detection efficiency between 3.6 MeV and 15.9 MeV. The obtained light response was used to adapt the simulation program SCINFUL to EJ309 scintillator. SCINFUL was then used to reproduce within 5 percent uncertainty the detector efficiency determined experimentally

The new double energy-velocity spectrometer VERDI

The conference in EPJ Web of Conferences entitled "ND 2016 International Conference on Nuclear Data for Science and Technology", ISBN: 978-2-7598-9020-0International audienceVERDI (VElocity foR Direct particle Identification) is a fission-fragment spectrometer recentlyput into operation at JRC-Geel. It allows measuring the kinetic energy and velocity of both fission fragmentssimultaneously. The velocity provides information about the pre-neutron mass of each fission fragment whenisotropic prompt-neutron emission from the fragments is assumed. The kinetic energy, in combination withthe velocity, provides the post-neutron mass. From the difference between pre- and post-neutron masses, thenumber of neutrons emitted by each fragment can be determined. Multiplicity as a function of fragment massand total kinetic energy is one important ingredient, essential for understanding the sharing of excitationenergy between fission fragments at scission, and may be used to benchmark nuclear de-excitation models.The VERDI spectrometer design is a compromise between geometrical efficiency and mass resolution. Thespectrometer consists of an electron detector located close to the target and two arrays of silicon detectors,each located 50 cm away from the target. In the present configuration pre-neutron and post-neutron massdistributions are in good agreement with reference data were obtained. Our latest measurements performedwith spontaneously fissioning 252Cf is presented along with the developed calibration procedure to obtainpulse height defect and plasma delay time corrections

Measuring correlated fission observables in Cf-252 with the VERDI spectrometer

International audienceVERDI (VElocity foR Direct particle Identification) is a double energy -double velocity (2E-2v) spectrometer under development at JRC-Geel. Both thephysical setup and the analysis have been improved upon since it first becameoperational in 2015. Currently, the spectrometer is being steadily improved using aCf-252(sf) source.Measuring the velocities allows computation of the pre-neutron masses and togetherwith the kinetic energy measurements, also the post-neutron masses can beobtained. Knowing both pre- and post-neutron masses allow calculating the averageneutron multiplicity as a function of fragment mass. Contrary to the 2E method, the2E-2v method does not need prior information regarding prompt neutron emission.Therefore, VERDI presents an independent means to assess neutron multiplicitydata correlated with other fission observables, helping to understand how theexcitation energy is shared between nascent fragments as well as benchmarkingnuclear de-excitation models.To date our results indicate a superior pre-neutron mass resolution compared to 2Edata obtained, e.g., using ionisation chambers. By implementing a new energycalibration method, based on the commonly used parametrisation proposed bySchmitt et al., we have improved the overall agreement with previous Cf-252 data. Inconsequence new and lower values for the set of Schmitt parameters were obtained.As the overall agreement is convincingly good, still VERDI show some discrepancies,e.g., the pre-neutron mass yields are higher for several high yield nuclei. Thepronounced structures are possibly due to the higher pre-neutron mass resolutionreached with VERDI. However, at present stage the post-mass resolution remains acritical feature to improve upon, which will be one focus in our future work.We will present the successful proof-of-principle that does not only show thefeasibility of the VERDI setup but also the benefits to obtain correlated fission-yielddata independent from previous measurements

Performance validation of the first arm of FALSTAFF: 252^{252}Cf and 235^{235}U fission fragment characterisation

International audienceThe renewed interest for the study of nuclear fission is mainly motivated by the development of GEN-IV reactor concepts, mostly foreseen to operate in the fast neutron energy domain. To support this development, new high-quality nuclear data are needed. In this context, a new experimental setup, the FALSTAFF spectrometer, dedicated to the study of nuclear fission is under development. Employing the double-velocity (2V) and energy-velocity (EV) methods, the fission fragment mass before and after neutron evaporation will be deduced and the correlation between prompt neutron multiplicity and fragment mass will be determined. The first arm of the spectrometer is achieved. It is composed of two SED-MWPC detectors (a combination of a foil to produce secondary electrons and a Multi-Wire Proportional Chamber to detect them) and an axial ionization chamber. The SED-MWPC give access to the velocity (V) via time-of-flight and position measurements. The ionization chamber measures the fragment kinetic energy (E) and the energy loss profile. Preliminary results for spontaneous fission of 252Cf and from the thermal-neutron induced fission experiment on 235U, performed at the Orphée reactor (CEA-Saclay, France), are presented