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A recent experimental campaign performed at the LOHENGRIN spectrometer at ILL aimed at measuring the independent fission yield of 136Cs in the 239Pu(nth,f) reaction. This nuclide can have an important contribution to the total dose rate coming from spent light water reactor UOX and MOX fuels. Moreover, its impact is of first order on the uncertainty of the total dose rate calculated in specific areas of Nuclear Power Plants within accidental conditions. One of the most important sources of uncertainty is its independent fission yield. Therefore, a new measurement of its independent yield along with a rigorous uncertainty analysis was performed. Due to its low independent yield, a new measurement technique has been applied. Ions recoiling from neutron-irradiated 239Pu target were collected by implantation into an Al foil placed inside a vacuum chamber. This foil was then transferred to a low γ-ray background setup located at nearby laboratory (LPSC). The procedure was then repeated for different LOHENGRIN settings. Compared to the JEFF-3.1.1 library, a decrease of the fission yield of 136Cs with a reduced uncertainty is obtained. [ABSTRACT FROM AUTHOR]

Despite the numerous theoretical and experimental works published very recently, the way in which fission fragments acquire their angular momentum is still an open question. This angular momentum generation mechanism is important not only for improving our understanding of the fission process, but also for nuclear energy applications, since the angular momentum of fission fragments strongly impact the prompt gamma spectra and consequently the decay heat in a reactor. In this context, within the framework of a collaboration between the 'Laboratoire de Physique Subatomique et Corpusculaire' (LPSC, France), the 'Institut Laue Langevin' (ILL, France) and the CEA-Cadarache (France), an experimental program was developed on the LO-HENGRIN mass-spectrometer with the aim of measuring isomeric ratio of some fission products for different thermal-neutron-induced fission reactions. This paper will be focused on the results obtained for the spherical nucleus 132Sn following thermal-neutron-induced fission of both 235U and 241Pu targets. To further challenge the angular momentum generation models, 132Sn isomeric ratio (IR) was measured as a function of 132Sn fission product kinetic energy (KE). The angular momentum was determined by combining our experimental data with the calculations performed with the FIFRELIN Monte Carlo code. A clear angular momentum decrease with KE was observed for both reactions. Lastly, we investigate the dependence of the 132Sn angular momentum with the incident neutron energy, from thermal region up to 5 MeV (below the second-chance fission). For that, the four free available parameters in FIFRELIN are selected in order to reproduce the average prompt neutron multiplicity. In this way, the angular momentum is deduced for each neutron energy. These results are discussed in terms of the impact of the available intrinsic excitation energy at scission on the spin generation mechanism. [ABSTRACT FROM AUTHOR]

The VElocity foR Direct particle Identification spectrometer (VERDI) is a 2E-2v fission spectrometer that allows the measurement of the total mass distribution of secondary fission fragments with a resolving power of 1-2 u. It consists of two time-of-flight (ToF) arms, with one Micro Channel Plate (MCP) detector and up to 32 Silicon PIPS (Passive Implanted Planar Silicon) detectors per arm. The MCPs provide the start timing signals and the PIPS detectors provide both the energy and the stopping ToF signals. In real conditions, the PIPS signals are affected by the formation of plasma from the interaction between the heavy ions and the detector material. The plasma contributes to a reduction in signal amplitude, resulting in a Pulse Height Defect (PHD), and introduces a signal delay, known as Plasma Delay Time (PDT). An experiment to characterize the PDT and PHD was performed at the LOHENGRIN recoil separator of the Institut Laue Langevin (ILL). Characteristic fission fragments from the 239Pu(n,f) reaction were separated based on their A/Q and E/Q ratios, allowing the measurement of a wide range of energies from 21 to 110 MeV and masses between 80 and 149 u. Six PIPS detectors were characterized to study their individual responses to the PDT and PHD effects. The signals were recorded in a digital acquisition system to completely exploit the offline analysis capabilities. Achieved combined timing and energy resolutions for fission fragments varied between 72(2) ps and 100(4) ps and 1.4% - 2% (FWHM), respectively. Preliminary PHD and PDT data are presented from the masses A=85, 95, 130 and 143. The PHD trends are strongly correlated with both the ion energy and mass. The PDT, on the other hand, shows a strong variation as a function of the ion kinetic energy but a smaller dependence on the ion mass. [ABSTRACT FROM AUTHOR]

During an experimental campaign performed at the LOHENGRIN recoil spectrometer of the Institut Laue-Langevin (ILL), a kinetic energy dependence of 132Sn fission product isomeric ratio (IR) has been measured by inducing thermal fission of 241Pu. The IRs are deduced using gamma ray spectrometry in coincidence with the ionisation chamber. To interpret these data, we use the FIFRELIN Monte-Carlo code to simulate the de-excitation of the fission fragments. Combining the IRs with the FIFRELIN calculations, the angular momentum distribution with kinetic energy of the doubly magic nucleus of 132Sn was deduced. This will be compared with the angular momentum distribution obtained for the reaction 235U(nth,f) for 132Sn. [ABSTRACT FROM AUTHOR]

To study the nuclear structure of neutron-rich titanium isotopes, a lifetime measurement was performed at the Grand Accélérateur National d'Ions Lourds (GANIL) facility in Caen, France. The nucleiwere produced in a multinucleon-transfer reaction by using a 6.76 MeV/u 238U beam. The Advanced Gamma Tracking Array (AGATA) was employed for the γ-ray detection and target-like recoils were identified event-by-event by the large-acceptance variable mode spectrometer (VAMOS++). Preliminary level lifetimes of the (5/2−) to 13/2− states of the yrast band in the neutron-rich nucleus 53Ti were measured for the first time employing the recoil distance Doppler-shift (RDDS) method and the compact plunger for deep inelastic reactions. The differential decay curve method (DDCM) was used to obtain the lifetimes from the RDDS data. [ABSTRACT FROM AUTHOR]

The evolution of the deformation across the Y isotopic chain, in the vicinity of N = 60 boundary, has been studied using gamma spectroscopy methods. The nuclei of interest have been produced by neutron induced fission of 235U and 241Pu targets, during two experimental campaigns named EXILL and FIPPS at the Institute Laue-Langevin in Grenoble. The emitted gamma rays have been collected by HPGe and LaBr3 detectors providing the identification of the high-spin levels in the 94Y and 96Y isotopes up to 6 MeV excitation energy, as well as information about the half-lives of the in-band states in the 98Y nucleus. The obtained results shed new light on the onset of deformation in the neutron-rich Y isotopes and, in general, in the A ≈ 100 region. [ABSTRACT FROM AUTHOR]