Neutron-transmission measurements through samples of magnesium fluoride (MgF2) and pure magnesium were performed to obtain neutron resonance parameters from all involved isotopes, 19F and 24-26Mg, in the range from 10 to 360 keV. Lithium-glass detectors were used in conjunction with the neutron Time of Flight technique. The measurement campaign was performed at the MONNET fast-neutron source of the European Commission Joint Research Centre (JRC-Geel, Belgium). Highly precise corrections for multiple scattering were calculated using a sophisticated iterative method based on Monte Carlo simulations with MCNP6.3 code, accounting for the effects of the experimental setup. With the SAMMY code, an R-Matrix analysis of the experimental data was performed. The extracted resonance widths, spins, and parities, as well as the limitations of the method, are carefully discussed.

Neutron-transmission measurements through samples of magnesium fluoride (MgF_2) and pure magnesium were performed to obtain the (n, tot) cross section for all isotopes involved, ^19F and ^24-26Mg. Lithium-glass detectors were used in conjunction with the neutron time-of-flight technique. The measurement campaign was performed at the MONNET fast-neutron source of the European Commission Joint Research Centre (JRC-Geel, Belgium). Highly precise corrections for multiple scattering were calculated using a sophisticated iterative method based on Monte Carlo simulations with the MCNP6.3 code, accounting for the effects of the experimental setup. With the SAMMY code, an R-Matrix analysis of the experimental data was performed. The extracted cross-sections, resonance spin and parity as well as the limitations of the method are carefully discussed.

The dual-mode elpasolite scintillation material CLLBC (Cs2LiLaBr4.8Cl1.2:Ce) is capable of measuring both y-rays and neutrons. The neutron detection capability spans from thermal energies up to about 10 MeV, making these detectors attractive options for studying prompt fission neutron spectra (PFNS). In this work, a comprehensive characterization of CLLBC detectors is performed. Three CLLBC detectors were characterized, in addition to three LaBr3:Ce and two LaBr3:Ce,Sr for comparison. For the best-performing CLLBC detector, the results indicate an energy resolution of 3.7% at Ey = 662 keV and an intrinsic timing resolution of 1.2 ns (FWHM) above Ey = 1 MeV using 60Co. A y-neutron separation figure-of-merit of 2.7 is obtained by means of pulse-shape discrimination. Tagged neutron time-of-flight measurements were conducted using a 241Am9Be neutron source, by coincident detection of the 4.44 MeV y-ray and the neutron, to determine the intrinsic neutron detection efficiency between 2-6 MeV. Neutron detection efficiencies of about 0.2% for the 6Li(n,t)4He reaction and 1% for three types of (n,n ') reactions were obtained. Two of three investigated CLLBC detectors exhibit an energy peak asymmetry, resulting in worse performance, indicating scintillator quality issues and motivating further investigation. Future studies are anticipated using the 252Cf(sf) prompt fission neutron spectrum to determine neutron efficiencies for a wider range of neutron energies. Although observed in a previous study, neutron detection via 35Cl(n,p)35S was not identified in this work but is planned to be determined using quasi-monoenergetic neutrons generated at the JRC MONNET facility.

Isomers produced by spontaneous fission of ^252 Cf were measured with the VESPA setup, composed of LaBr_3 (Ce) detectors for fast γ -ray spectroscopy and an ionization chamber for detecting fission fragments. Identification of the isomers was derived from fission fragment- γ - γ coincidences. This paper presents the half-lives of 41 isomeric states measured with this setup, from less than a nanosecond up to tens of microseconds. Short-lived isomers in ^94 Rb, ^108 Tc, and ^147 Ce are reported for the first time. In addition to this half-life analysis, the isomers are used to develop and test a nuclear charge calibration of the ionization chamber.

This paper describes cross-section measurements of fast-neutron-induced reactions using the neutron activation method. The study employed two accelerator-driven fast neutron sources, each possessing distinct characteristics during irradiation of analogous sets of samples. Specifically, the neutron source at the NPI & Rcaron;e & zcaron; relied on the p+Li(C) reaction, while MONNET at JRC Geel utilized the d+TiT(Ag) reaction for neutron production. Building upon prior experiments conducted at NPI, we present new cross-sections for reactions, some of which suffer from a dearth of experimental data. The results presented in this paper originate from samples of Al, Au, Bi, Co, NaF, and Y that were irradiated with neutrons at energies of 17.6(3) MeV, and 18.5(4) MeV at MONNET, and an energy of 22.5(8) MeV at the NPI. Following neutron irradiation, the samples were analysed using gamma-ray spectrometry. Cross-sections of several fast-neutron-induced reactions were determined on the basis of the measurement of neutron spectra and corresponding reaction yields. By comparing the results of analogous experiments conducted indifferent experimental setups, it becomes possible to assess systematic uncertainties. The obtained cross-sections may contribute to the further development of both advanced nuclear reactors and to a more precise fast-neutron dosimetry.

The VERDI fission spectrometer is designed to measure fragment velocities and kinetic energies to achieve high-precision yield measurements. It consists of two time-of-flight (TOF) sections, each hosting a micro-channel plate (MCP) and up to 32 passivated implanted planar silicon (PIPS) detectors. The main challenge to achieve accurate fragment velocities is the so-called plasma delay time (PDT) phenomena in the PIPS detectors. In this work, we present a dedicated experimental campaign at the LOHENGRIN fission-fragment recoil separator, to solve the pending PDT challenges. The PDT effect was systematically investigated, as a function of mass and energy, using a dedicated time-of-flight setup. In addition, the pulse height defect (PHD) was determined simultaneously. The studies were conducted for five PIPS detectors, in energies and mass numbers ranging from 20 to 110 MeV and A = 85 to 149, respectively. Using digital signal processing, an excellent timing resolution was achieved, reaching as low as 60 ps (one σ ) for the heavy ions. The PDT revealed a strong positive correlation with the ion energy and a weak negative correlation with the mass. The experimental PDT values determined from five detectors confirm a consistent systematic behavior with respect to mass and energy. Some systematic discrepancies were exhibited by two detectors, possibly due to the use of different pre-amplification chains. The PDT measurements ranged between 1 and 3.5 ns, for heavy ions relative to α -particles. The PHD values showed also a strong correlation with the ion energy, and moreover with the ion mass. The PHD for heavy ions was found to range between 2 and 8 MeV, relative to α -particles. Finally, a two-dimensional parameterisation was developed to model the experimental PDT data, as a function of mass and energy. This new model, which is valid in the fission fragment mass and energy regime, will be of benefit for heavy-ion velocity measurements, using silicon detectors, as done in VERDI.

A programme to study photon- and neutron-induced reactions of medical interest, as well as accelerator-based methods of medical radionuclide production, has been instituted at JRC-Geel, making use of both existing and new infrastructure. A new electron beamline that can deliver quasi-monoenergetic beams has been commissioned at the GELINA electron linac and will be primarily dedicated to the study of photonuclear reactions and for medical radioisotope production studies via photon irradiation. The recently renewed MONNET 3.5 MV Tandem accelerator provides light ion beams for reactionbased quasi-mono-energetic neutron production and has been used for the study of 99Mo production via neutron irradiation of molybdenum nanoparticles. In this work we present an overview of the medical radionuclide activities at JRCGeel, with particular attention to aspects of the design, development and operational challenges of the new GELINA electron beamline. Some future perspectives of the programme are also discussed.

The design of new generation fast nuclear reactors requires highly accurate cross-section measurements in the MeV energy region. The 242Pu fission cross section is of particular interest for Pu incineration and nuclear waste production. There are discrepancies around 1 MeV incident neutron energy between libraries and among experimental data. Some data suggest the presence of a strong structure between 1 and 1.2 MeV whereas it is barely visible on some other data and its shape is very different among evaluations. The large majority of the 242Pu(n,f) measurements have been carried out with respect to the 235U(n,f) secondary-standard cross section. This introduces a strong correlation between measurements from different research teams. Moreover, this reference cross section exhibits structures, in particular a steep increase of +10% at 1 MeV. Therefore, we aim to re-measure the 242Pu(n,f) cross section relative to the primary-standard 1H(n,n)p cross section, by using a proton recoil detector. This standard has a very high accuracy (0.4%), is not used for other 242Pu measurements, and is structureless. An experiment has been carried out in October 2022 at the MONNET facility in JRC Geel, with incident neutron energies from 0.9 MeV to 2.0 MeV. The experimental setup will be presented, and the analysis procedure will be detailed.

The FIFRELIN Monte Carlo code has been upgraded recently by adding new capabilities, additional models and updated databases. Several examples are presented in this work as well as three different applications related to the prompt component in fission, gamma cascades from thermal neutron capture and the delayed component in fission associated to the time evolution of decay heat.

We report on high-resolution laser spectroscopy studies on 249-253Cf with spectral linewidths in the order of 100 MHz carried out at the RISIKO mass separator at Mainz University. In total three atomic ground-state transitions were investigated and the hyperfine parameters for the odd-A isotopes and isotope shift for all examined isotopes have been determined from the measured spectra. The isotope shift measurements allowed tracking of changes in mean-squared charge radii across the deformed nuclear shell closure at N = 152, whereby shape discontinuities were not observed. Experimental hyperfine coupling constants of the atomic ground state were combined with relativistic many-body atomic calculations to extract the nuclear magnetic-dipole moment of 249Cf with improved precision to mu I(249Cf) = -0.395(17 )mu N, whereas mu I(251Cf) = -0.571(24 )mu N and mu I(253Cf) = -0.731(35 )mu N were derived for the first time. Additionally, the spectroscopic quadrupole moments QS(249Cf) = 6.27(33) eb and QS(253Cf) = 5.53(51) eb were extracted.

Nuclear fission is a process that very soon after its discovery was understood as tunneling through a barrier. This barrier refers to a structure in the potential-energy landscape, whose description has considerably changed with time due to a fruitful interaction between experimental results and theoretical modeling. Since barrier parameters in general are not directly accessible by experiments, we give an overview of important observations related to fission, theoretical descriptions of the barrier, and how information on the barrier may be deduced experimentally. Hence, in this chapter, we try to summarize this development from more than 80 years ago to present day's knowledge and give an outlook on promising new approaches.

Medium spin states of light N = 50 isotones have been populated using fast neutron-induced fission of ^232 Th. Online prompt γ spectroscopy has been performed using the hybrid γ spectrometer ν- Ball coupled to the LICORNE directional neutron source at the ALTO facility of IJCLab. Medium spin states of the neutron-rich nucleus ^82 Ge have been investigated using γ - γ and γ - γ - γ coincidence data to exploit the resolving power of ν- Ball. Two new transitions were assigned to this nucleus and a new level was placed in the level scheme. We tentatively assigned to this new state a ( 7^+ ) spin-parity, which is interpreted as a new N=50 core breaking state. This provides further insight into the energy evolution of the N=50 shell gap toward ^78 Ni.

The population of isomeric states in the prompt decay of fission fragments-so-called isomeric yield ratios (IYRs)-is known to be sensitive to the angular momentum J that the fragment emerged with, and may therefore contain valuable information on the mechanism behind the fission process. In this work, we investigate how changes in the fissioning system impact the measured IYRs of fission fragments to learn more about what parameters affect angular momentum generation. To enable this, a new technique for measuring IYRs is first demonstrated. It is based on the time of arrival of discrete gamma rays, and has the advantage that it enables the study of the IYR as a function of properties of the partner nucleus. This technique is used to extract the IYR of 134Te, strongly populated in actinide fission, from the three different fissioning systems: 232Th(n, f), 238U(n, f), at two different neutron energies, as well as 252Cf(sf). The impacts of changing the fissioning system, the compound nuclear excitation energy, the minimum J of the binary partner, and the number of neutrons emitted on the IYR of 134Te are determined. The decay code TALYS is used in combination with the fission simulation code FREYA to calculate the primary fragment angular momentum from the IYR. We find that the IYR of 134Te has a slope of 0.004 +/- 0.002 with increase in compound nucleus (CN) mass. When investigating the impact on the IYR of increased CN excitation energy, we find no change with an energy increase similar to the difference between thermal and fast fission. By varying the mass of the partner fragment emerging with 134Te, it is revealed that the IYR of 134Te is independent of the total amount of prompt neutrons emitted from the fragment pair. This indicates that neutrons carry minimal angular momentum away from the fission fragments. Comparisons with the FREYA+TALYS simulations reveal that the average angular momentum in 134Te following 238U(n, f) is 6.0 h over bar . This is not consistent with the value deduced from recent CGMF calculations. Finally, the IYR sensitivity to the angular momentum of the primary fragment is discussed. These results are not only important to help understanding the underlying mechanism in nuclear fission, but can also be used to constrain and benchmark fission models, and are relevant to the gamma -ray heating problem of reactors.

Actinide and lanthanide thin layers with specific requirements regarding thickness, homogeneity, chemical purity, mechanical stability, and backing properties are applied in a multitude of physics and chemistry experiments. A novel target preparation method, the so-called “Drop-on-Demand” (DoD) technique, based on a commercial nanoliter (nL) dispenser is applied since a few years in the Nuclear Chemistry unit at Johannes Gutenberg University Mainz. The wetting behaviour of the nL droplets on the substrate’s surface is a key parameter determining the spatial distribution of the deposited material after evaporation. By switching from aqueous to organic solvents as well as by substrate surface modifications, the wetting behaviour can be influenced. Recent investigations on this influence and applications of the DoD method are presented. The produced actinide deposits were characterized by optical and scanning electron microscopy, by α spectroscopy as well as by radiographic imaging.

MONNET is a fast-neutron source based on a 3.5 MV tandem accelerator, located at the Geel (BE) site of the Joint esearch Centre. It became operational in 2020. MONNET may deliver intense neutron beams in the energy range from 30 keV to 10.1 MeV and from 12.8 MeV to 24 MeV. Neutrons are generated by means of nuclear reactions in the target material (e.g. protons or deuterons on lithium-7, tritium or deuterium targets). MONNET delivers a neutron flux of up to 109 n/sr/s, depending on the producing reaction and the neutron energy. Neutron beams are essentially mono-energetic (∆En/En < 6% with En > 300 keV). The accelerator may also be used with proton and deuteron beams. Alpha beams will be offered soon. Photon beams are possible and presently under investigation. The research program ranges from cross section measurements, e.g. (n, f), (n, p), (n, α) as well as (p, p′), (p, n) and (p, γ), nuclear fission research, material studies (e.g. radiation-induced damage), to the investigation of advanced methods in nuclear technologies, safety and security. The MONNET neutron source offers beamtime to external user within the JRC EUFRAT Open Access program. Proposal evaluation by an independent panel is taking place up to two times per year.

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.

Monte-Carlo simulations to calculate the number of prompt particles emitted during fission were performed using the Fifrelin code and compared to recent experimental data. We show that we are able to reproduce both the neutron and γ-ray multiplicity distributions as a function of the pre-neutron mass of the fission fragments using a single consistent set of parameters. This result was made possible by using an energy-dependent spin cut-off model, driving the initial total angular momentum of the fission fragments, together with microscopic level densities from the HFB plus combinatorial method. We also discuss, how the initial excitation-energy sharing shapes the TKE-dependent γ-ray multiplicity.