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Background: Angular momenta of fission fragments considerably higher than that of the fissioning nucleus have been observed in many experiments, raising the question of how these high angular momenta are generated. Wilson et al. have proposed a model for the angular momentum as a function of the mass of fission products based on the assumption that the angular momentum is generated from the collective motion of nucleons in the ruptured neck of the fissioning system. This assumption has caused a lot of debate in the community. Purpose: To estimate the angular momenta of fission fragments based on the observed isomeric yield ratios in 25 -MeV proton -induced fission of 238 U. Method: A surrogate model of the fission code general description of fission observables (GEF) has been developed to generate properties of primary fission fragments. Based on the excitation energy and angular momentum of fission fragments from GEF, an energy -versus -angular -momentum matrix is reconstructed using a set of parameters. With such matrices as input, the reaction code TALYS is used to calculate the deexcitation of the fission fragments, including the population of the isomers, from which the isomeric yield ratios are obtained. By varying one of the parameters, the root -mean -square angular momentum ( J rms ), which determines the angular momentum distribution of the matrix, J rms -dependent isomeric yield ratios are obtained. Considering all primary fission fragments contributing to the isomeric yield ratio for a given fission product, the average angular momentum of those fragments is estimated. Results: Data of 31 isomeric yield ratios in 25 -MeV proton -induced fission of 238 U were analyzed. From the analysis, the average J rms , equivalent to average angular momentum J av , with uncertainties are obtained for 24 fission products, while in seven cases no conclusive result for the angular momentum could be obtained. Furthermore, considering the neutron emissions of the primary f

Background: Isomeric yield ratios are an important observable in nuclear fission as they can guide model development by providing insight into the angular momentum generation. Furthermore, isomeric yield ratios are important in applications for nuclear energy, as well as in the study of the r-process in stellar nucleosynthesis, and in the antineutrino mixing angle from reactor spectra. In nuclear data evaluations, the Madland-England model is commonly used to estimate isomeric yield ratios that have not been measured. Purpose: To measure isomeric yield ratios in 25-MeV proton-induced fission of 238U, and to compare the result with the values obtained from the Madland-England model and the fission model code GEF. Furthermore, to evaluate whether the predictions of GEF can be improved by coupling it to the nuclear reaction code TALYS. Methods: Isomeric yield ratios in 25-MeV proton-induced fission of 238U have been measured at the Ion GuideIsotope Separate On-Line facility. The excited state and the ground state were separated by mass using the Phase-Imaging Ion-Cyclotron-Resonance technique in the double Penning trap JYFLTRAP. The number of counts of each state was extracted from the phase-images using a Bayesian Gaussian Mixture model and, after corrections fordetector efficiency and decay, the isomeric yield ratios were derived. The experimental values have been compared with the calculated results from the Madland-England model and the GEF code. Furthermore, GEF has been combined with the nuclear reaction code TALYS, in order to take advantage of the latter codes’ implementation of the Hauser-Feshbach formalism, and the results have been compared with the experimental values. Results: From the measurements, 19 new isomeric yield ratios in 25-MeV proton-induced fission of 238U are reported and are, together with another 12 isomeric yield ratios (IYRs) from a previous campaign, compared with the model calculations. It is shown that, though the models manage to captu

Measurements of independent fission yield distributions in neutron-induced fission at high neutron energies are important for our fundamental understanding of the fission process, and are also relevant for reactor physics applications. So far, measurements of independent fission yields in proton-induced fission have been performed at the IGISOL facility at the University of Jyväskylä, using the Penning trap as a high resolving-power mass-filter. In order to also facilitate measurements of neutron-induced fission, a dedicated ion guide and a proton-to-neutron converter was developed. However, the first measurement indicates that fewer fission products than expected reach the Penning trap. To explore potential reasons and possible improvements, a simulation model was also developed and benchmarked. The benchmark showed that the model is able to reproduce the performance of the ion guide remarkably well and that the main reason for the low yield of fission products is the low collection efficiency of the ion guide. Based on the benchmark, a new ion guide is being designed. In the new design, the positions of the uranium targets and volume of the ion guide have been changed to increase the collection of fission products. This results in a five-fold increase of the yield. However, the collection efficiency of the new ion guide still needs to be improved in order to achieve intensities of the extracted fission products that are large enough to allow for reasonable measurement times. Because the volume of the ion guide is increased significantly, the extraction time of the ions is expected to be longer than that from the previous ion guide. Therefore, an electric field guidance system that consists of a combination of a stationary electric field and an RF-carpet is considered to be deployed. The stationary field, produced from a set of DC-ring electrodes, accelerates the ions towards the RF-carpet at end plate of the ion guide. The RF-carpet consists of a time-dependent fi

In a measurement of isomeric yield-ratios in fission, the Phase-Imaging Ion-Cyclotron-Resonance technique, which projects the radial motions of ions in the Penning trap (JYFLTRAP) onto a position-sensitive micro-channel plate detector, has been applied. To obtain the yield ratio, that is the relative population of two states of an isomer pair, a novel analysis procedure has been developed to determine the number of detected ions in each state, as well as corrections for the detector efficiency and decay losses. In order to determine the population of the states in cases where their mass difference is too small to reach full separation, a Bayesian Gaussian Mixture model was implemented. The position-dependent efficiency of the micro-channel plate detector was calibrated by mapping it with 133Cs+ ions, and a Gaussian Process was trained with the position data to construct an efficiency function that could be used to correct the recorded distributions. The obtained numbers of counts of excited and ground-state ions were used to derive the isomeric yield ratio, taking into account decay losses as well as feeding from precursors.

Nucleon knockout experiments using beryllium or carbon targets reveal a strong dependence of the quenching factors, i.e., the ratio (Rs) of theoretical to the experimental spectroscopic factors (C2S), on the proton-neutron asymmetry in the nucleus under study. However, this dependence is greatly reduced when a hydrogen target is used. To understand this phenomenon, exclusive H-1(Ne-17, 2p F-16) and inclusive C-12(Ne-17, 2p 1(6)F)X, 1(2)C(Ne-17, F-16)X as well as 1H(Ne-17,(16) F)X(X-denotes undetected reaction products) reactions with F-16 in the ground and excited states were anal- ysed. The longitudinal momentum distribution of F-16 and the correlations between the detached protons were studied. In the case of the carbon target, there is a significant deviation from the predictions of the eikonal model. The eikonal approximation was used to extract spectroscopic factor values (CS)-S-2. The experimental (CS)-S-2 value obtained with C target is markedly lower than that for H target. This is interpreted as rescattering due to simultaneous nucleon knockout from both reaction partners, Ne-17 and C-12.

The proton drip-line nucleus Ne-17 is investigated experimentally in order to determine its two-proton halo character. A fully exclusive measurement of the Ne-17(p, 2p)F-16* -> O-15+p quasi-free one-proton knockout reaction has been performed at GSI at around 500MeV/nucleon beam energy. All particles resulting from the scattering process have been detected. The relevant reconstructed quantities are the angles of the two protons scattered in quasi-elastic kinematics, the decay of F-16 into O-15 (including gamma decays from excited states) and a proton, as well as the O-15+p relative-energy spectrum and the F-16 momentum distributions. The latter two quantities allow an independent and consistent determination of the fractions of l = 0 and l = 2 motion of the valence protons in Ne-17. With a resulting relatively small l = 0 component of only around 35(3)%, it is concluded that Ne-17 exhibits a rather modest halo character only. The quantitative agreement of the two values deduced from the energy spectrum and the momentum distributions supports the theoretical treatment of the calculation of momentum distributions after quasi-free knockout reactions at high energies by taking into account distortions based on the Glauber theory. Moreover, the experimental data allow the separation of valence-proton knockout and knockout from the O-15 core. The latter process contributes with 11.8(3.1) mb around 40% to the total proton-knockout cross section of 30.3(2.3) mb, which explains previously reported contradicting conclusions derived from inclusive cross sections. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).

To enhance the production of medium-heavy,neutron-rich nuclei, and to facilitate measurements of independentyields of neutron-induced fission, a proton-toneutronconverter and a dedicated ion guide for neutroninducedfission have been developed for the IGISOL facilityat the University of Jyväskylä. The ion guide holds thefissionable targets, and the fission products emerging fromthe targets are collected in helium gas and transported to thedownstream experimental stations.Acomputer model, basedon a combination of MCNPX for modeling the neutron production,the fission code GEF, and GEANT4 for the transportof the fission products, was developed. The model willbe used to improve the setup with respect to the productionand collection of fission products. In this paper we benchmarkthe model by comparing simulations to a measurementin which fission products were implanted in foils located atdifferent positions in the ion guide. In addition, the productsfrom neutron activation in the titanium foil and the uraniumtargets are studied. The result suggests that the neutron fluxat the high-energy part of the neutron spectrum is overestimatedby approximately 40%.However, the transportation offission products in the uranium targets agrees with the experimentwithin 10%. Furthermore, the simulated transportationof fission products in the helium gas achieves almost perfectagreement with the measurement. Hence, we conclude thatthe model, after correction for the neutron flux, is well suitedfor optimization studies of future ion guide designs.

The generation of angular momentum in the fission process is still an open question. To shed light on this topic, we started a series of measurements at the IGISOL-JYFLTRAP facility in Finland. Highprecision measurements of isomeric yield ratios (IYR) are performed with a Penning trap, partly with the aim to extract average root-mean-square (rms) quantities of fragment spin distributions. The newly installed Phase-Imaging Ion-Cyclotron Resonance (PI-ICR) technique allows the separation of masses down to tens of keV, which is suffcient to disentangle many isomers. In this paper, we first summarize the previous measurements on the neutron and proton-induced fission of uranium and thorium, e.g. the odd cadmium and indium isotopes (119 ≤ A ≤ 127). The measurements revealed systematic trends as function of mass number, which stimulated further exploration. A recent measurement was performed at IGISIOL and several new IYR data will soon be published, for the first time. Secondly, we employ the TALYS nuclear-reaction code to model one of the newly measured isomer yields. Detailed GEF and TALYS calculations are discussed for the fragment angular momentum distribution in 134I.

In a Swedish citizen science project, more than 200 elementary school classes participated in collecting fungi, soil samples, and droppings from deer and wild boar, from all over Sweden. The samples have been sent to a laboratory at Uppsala University where they are being analyzed through gamma spectroscopy with a shielded HPGe detector. The main objective is to scan the samples for 137Cs from the Chernobyl accident and compare the data with measurements from 1986, but uptake of naturally occuring radionuclides like 40K and radon daughters will also be determined. Together with the soil samples, transfer factors will be derived, and correlations for these factors will be sought for different species of fungi and soil types. The potential for correlating the results with different biological processes will also be investigated, in part through the collected animal droppings. This is a work in progress where the present status of the experimental setup and methodology are presented. Issues with the initial approach for corrections are discussed and preliminary results are presented.

A growing trend in science is that research institutions reach out to members of the public for participating in research. The reasons for outreach are many, spanning from the desire to collect and/or analyse large sets of data efficiently, to the idea of including the general public on a very fundamental level in science-making and ultimately decision-making. The presented project is curriculum-based and carried out in 240 lower secondary school classes (pupils of age 13-16). The task, as designed by the participating universities, is to collect mushrooms, soil and animal droppings from different parts of Sweden, do preliminary sample preparation and analyses and send the samples to the university institutions for radioactivity measurement. Behind the project is a desire to compare today’s levels of 137Cs with those deposited right after the Chernobyl accident in 1986, but also to study the exchange of caesium between organisms as well as the impacts of biological and geological processes on uptake and retention. The scientific outcome is a geodatabase with the 137Cs activity (Bq/m2) present in the Swedish environment, where radioactivity data can be linked to the species (fungi, competing species, animals foraging), forest type, land type, land use and other environmental factors. The science question is of interest to the general public as foraging for mushrooms, as well as spending recreational time in forests is widely popular in Sweden. In this article, we will discuss the current status of the project and the observations we have made about how well the public can participate in scientific research. Focus will be on organization of the project, such as logistics, preparation of supportive material, feedback and communication between researchers and schools. We will present observations about the impact the project has had on the participants, based on quantitative and qualitative evaluations.

For the production of exotic nuclei at the IGISOL facility, an ion guide for neutron-induced fission has been developed and tested in experiments. Fission fragments are produced inside the ion guide and collected using a helium buffer gas. Meanwhile, a GEANT4 model has been developed to simulate the transportation and stopping of the charged fission products. In a recent measurement of neutron-induced fission yields, implantation foils were located at different positions in the ion guide. The gamma spectra from these foils and the fission targets are compared to the results from the GEANT4 simulation. In order to allow fission yield measurements in the low yield regions, towards the tails and in the symmetric part of the mass distribution, the stopping and extraction efficiency of the ion guide has to be significantly improved. This objective can be achieved by increasing the size while introducing electric field guidance using a combination of static electrodes and an RF-carpet. To this end, the GEANT4 model is used to optimise the design of such an ion guide.

MeV-scale energy depositions by low-energy photons produced in neutrino-argon interactions have been identified and reconstructed in ArgoNeuT liquid argon time projection chamber (LArTPC) data. ArgoNeuT data collected on the NuMI beam at Fermilab were analyzed to select isolated low-energy depositions in the TPC volume. The total number, reconstructed energies, and positions of these depositions have been compared to those from simulations of neutrino-argon interactions using the FLUKA Monte Carlo generator. Measured features are consistent with energy depositions from photons produced by deexcitation of the neutrino's target nucleus and by inelastic scattering of primary neutrons produced by neutrino-argon interactions. This study represents a successful reconstruction of physics at the MeV scale in a LArTPC, a capability of crucial importance for detection and reconstruction of supernova and solar neutrino interactions in future large LArTPCs.

Isomeric yield ratios for the odd-A isotopes of Cd119-127 and In119-127 from 25-MeV proton-induced fission on natural uranium have been measured at the JYFLTRAP double Penning trap, by employing the phase-imaging ion-cyclotron-resonance technique. With the significantly improved mass resolution of this novel method isomeric states separated by 140 keV from the ground state, and with half-lives of the order of 500 ms, could be resolved. This opens the door for obtaining new information on low-lying isomers, which are important for nuclear structure, fission, and astrophysics. In the present work the experimental isomeric yield ratios are used for the estimation of the root-mean-square angular momentum J(rms) of the primary fragments. The results show a dependency on the number of unpaired protons and neutrons, where the odd-Z In isotopes carry larger angular momenta. The deduced values of J(rms) display a linear relationship when compared with the electric quadrupole moments of the fission products.

This work aims at measuring prompt-fission neutrons at different excitation energies of the nucleus. Two independent techniques, the 2E-2v and the 2E techniques, are used to map the characteristics of the mass-dependent prompt fission neutron multiplicity, 7(A), when the excitation energy is increased. The VERDI 2E-2v spectrometer is being developed at JRC-GEEL. The Fission Fragment (FF) energies are measured using two arrays of 16 silicon (Si) detectors each. The FFs velocities are obtained by time-of-flight, measured between micro-channel plates (MCP) and Si detectors. With MCPs placed on both sides of the fission source, VERDI allows for independent timing measurements for both fragments. Cf-252(sf) was measured and the present results revealed particular features of the 2E-2v technique. Dedicated simulations were also performed using the GEF code to study important aspects of the 2E-2v technique. Our simulations show that prompt neutron emission has a non-negligible impact on the deduced fragment data and affects also the shape of 17(A). Geometrical constraints lead to a total-kinetic energy-dependent detection efficiency. The 2E technique utilizes an ionization chamber together with two liquid scintillator detectors. Two measurements have been performed, one of Cf-252(sf) and another one of thermal-neutron induced fission in U-235(n,f). Results from Cf-252(sf) are reported here.

Data on fission yields and isomeric yield ratios (IYR) are tools to study the fission process, in particular the generation of angular momentum. We use the IGISOL facility with the Penning trap JYFLTRAP in Jyvaskyla, Finland, for such measurements on Th-232 and U-nat targets. Previously published fission yield data from IGISOL concern the Th-232(p,f) and U-238(p,f) reactions at 25 and 50 MeV. Recently, a neutron source, using the Be(p,n) reaction, has been developed, installed and tested. We summarize the results for (p,f) focusing on the first measurement of IYR by direct ion counting. We also present first results for IYR and relative yields for Sn and Sb isotopes in the 128-133 mass range from U-nat(n,f) based on gamma-spectrometry. We find a staggering behaviour in the cumulative yields for Sn and a shift in the independent fission yields for Sb as compared to current evaluations. Plans for the future experimental program on fission yields and IYR measurements are discussed.

We report the first experimental determination of independent isomeric yield ratios using direct ion counting with a Penning trap, which offered such a high resolution in mass that isomeric states could be separated. The measurements were performed at the Ion Guide Isotope Separator On-Line (IGISOL) facility at the University of Jyvaskyla. The isomer production ratios of Ge-81, Y-96,Y-97 Sn-128(,1)30, and Sb-129 in the 25-MeV proton-induced fission of U-na(t) and Th-232 were studied. Three isomeric pairs (Ge-81, Y-96, and Sb-129) were measured for the first time for the U-na(t)(p, f) reaction, while all the reported yield ratios for the Th-232(p, f) reaction were determined for the first time. The comparison of the experimentally determined isomeric yield ratios with data available in the literature shows a reasonable agreement, except for the case of Sn-130 for unspecified reasons. The obtained results were also compared with the GEF model, where good agreement can be noticed in most cases for both reactions. Serious discrepancies can only be observed for the cases of Y-96(,)97 for both reactions. Moreover, based on the isomeric yield ratios, the root-mean-square angular momenta (J(r)(ms)) of the fission fragments after scission were estimated using the TALYS code. The experimentally determined isomeric yield ratios, and consequently the deduced J(rms), for Sn-130 are significantly lower compared to Sn-128 for both fissioning systems. This can be attributed to the more spherical shape of the fragments that contribute to the formation of Sn-130, due to their proximity to the N = 82 shell closure. The values of J(rms) for Sb-129 are higher than Sn-128 for both reactions, despite the same neutron number of both nuclides (N = 78), indicating the odd-Z effect where fission fragments with odd-Z number tend to bear larger angular momentum than even-Z fragments. The isomer production ratio for the isotopes of Sn is more enhanced in the U-na(t)(p, f) reaction than in Th-232

The first systematic measurement of neutron-induced fission yields has been performed at the upgraded IGISOL-4 facility at the University of Jyvaskyla, Finland. The fission products from high-energy neutron-induced fission of U-nat were stopped in a gas cell filled with helium buffer gas, and were online separated with a dipole magnet. The isobars, with masses in the range A = 128-133, were transported to a tape-implantation station and identified using gamma-spectroscopy. We report here the relative cumulative isotopic yields of tin (Z = 50) and the relative independent isotopic yields of antimony (Z = 51). Isomeric yield ratios were also obtained for five nuclides. The yields of tin show a staggered behaviour around A = 131, not observed in the ENDF/B-VII. 1 evaluation. The yields of antimony also contradict the trend from the evaluation, but are in agreement with a calculation performed using the GEF model that shows the yield increasing with mass in the range A = 128-133.

The Borromean drip-line nucleus Ne-17 has been suggested to possess a two-proton halo structure in its ground state. In the astrophysical rp-process, where the two-proton capture reaction O-15(2p,gamma) Ne-17 plays an important role, the calculated reaction rate differs by several orders of magnitude between different theoretical approaches. To add to the understanding of the Ne-17 structure we have studied nuclear and electromagnetic dissociation. A 500 MeV/u Ne-17 beam was directed toward lead, carbon, and polyethylene targets. Oxygen isotopes in the final state were measured in coincidence with one or two protons. Different reaction branches in the dissociation of Ne-17 were disentangled. The relative populations of s and d states in F-16 were determined for light and heavy targets. The differential cross section for electromagnetic dissociation (EMD) shows a continuous internal energy spectrum in the three-body system O-15 + 2p. The Ne-17 EMD data were compared to current theoretical models. None of them, however, yields satisfactory agreement with the experimental data presented here. These new data may facilitate future development of adequate models for description of the fragmentation process.

A white neutron source based on the Be(p,nx) reaction for fission studies at the IGISOLJYFLTRAP facility has been designed and tested. 30 MeV protons impinge on a 5mm thick water-cooled beryllium disc. The source was designed to produce at least 1012 fast neutrons/s on a secondary fission target, in order to reach competitive production rates of fission products far from the valley of stability. The Monte Carlo codes MCNPX and FLUKA were used in the design phase to simulate the neutron energy spectra. Two experiments to characterise the neutron field were performed: the first was carried out at The Svedberg Laboratory in Uppsala (SE), using an Extended-Range Bonner Sphere Spectrometer and a liquid scintillator which used the time-of-flight (TOF) method to determine the energy of the neutrons; the second employed Thin-Film Breakdown Counters for the measurement of the TOF, and activation foils, at the IGISOL facility in Jyväskylä (FI). Design considerations and the results of the two characterisation measurements are presented, providing benchmarks for the simulations.

The nuclear de-excitation process of fission fragments (FF) provides fundamental information for the understanding of nuclear fission and nuclear structure in neutron-rich isotopes. The variation of the prompt-neutron multiplicity, ν(A), as a function of the incident neutron energy (En) is one of many open questions. It leads to significantly different treatments in various fission models and implies that experimental data are analyzed based on contradicting assumptions. One critical question is whether the additional excitation energy (Eexc) is manifested through an increase of ν(A) for all fragments or for the heavy ones only. A systematic investigation of ν(A) as a function of En has been initiated. Correlations between prompt-fission neutrons and fission fragments are obtained by using liquid scintillators in conjunction with a Frisch-grid ionization chamber. The proof-of-principle has been achieved on the reaction 235U(nth,f) at the Van De Graff (VdG) accelerator of the JRC-Geel using a fully digital data acquisition system. Neutrons from 252Cf(sf) were measured separately to quantify the neutron-scattering component due to surrounding shielding material and to determine the intrinsic detector efficiency. Prelimenary results on ν(A) and spectrum in correlation with FF properties are presented.

Independent isomeric yield ratios (IYR) of 81Ge, 96Y, 97Y, 97Nb, 128Sn and 130Sn have been determined in the 25 MeV proton-induced fission of natU and 232Th. The measurements were performed at the Ion Guide Isotope Separator On-Line (IGISOL) facility at the University of Jyväskylä. A direct ion counting measurement of the isomeric fission yield ratios was accomplished for the first time, registering the fission products in less than a second after their production. In addition, the IYRs of natU were measured by means of γ-spectroscopy in order to verify the consistency of the recently upgraded experimental setup. From the obtained results, indications of a dependence of the production rate on the fissioning system can be noticed. These data were compared with data available in the literature, whenever possible. Using the TALYS code and the experimentally obtained IYRs, we also deduced the average angular momentum of the fission fragments after scission.

Codes for the calculation of fission observables are frequently used to describe experimentally observed phenomena as well as provide predictions in cases where measurements are missing. Assumptions in the models, and tuning of parameters within the codes, often result in a good reproduction of experimental data. In this work we propose a methodology, coded in the newly developed program DELFIN (De-Excitation of FIssion fragmeNts), that can be used to compare some of the assumptions of the various models. Our code makes use of the fission fragments information after scission and processes them in an independent and consistent fashion to obtain measurable fission observables (such as ν(A) distributions and Isomeric Fission Yield ratios). All the available information from the models, such as fragments' excitation energies, spin distributions and yields are provided as input to DELFIN that uses the nuclear reaction code TALYS to handle the de-excitation of the fission fragments. In this way we decouple the fragments relaxation from the actual fission models. We report here the first results of a comparison carried out on the GEF, Point-by-Point and FREYA models for thermal fission of 235U and 239Pu and spontaneous fission of 252Cf.

With the Ion Guide Isotope Separator On-Line (IGISOL) facility, located at the University of Jyväskylä, products of nuclear reactions are separated by mass. The high resolving power of the JYFLTRAP Penning trap, with full separation of individual nuclides, capacitates the study of nuclides far from the line of stability. For the production of neutron-rich medium-heavy nuclides, fissioning of actinides is a feasible reaction. This can be achieved with protons from an in-house accelerator or, alternatively, with neutrons through the addition of a newly developed Be(p,xn)-converter. The hereby-obtained fission products are used in nuclear data measurements, for example fission yields, nuclear masses, Q-values and decay spectroscopy. Prior to separation, the ionized reaction products are stopped in a helium-filled gas cell, referred to as the ion-guide. In this work we present simulations of the stopping of fission products in an ion guide developed for neutron-induced fission. The production and extraction rates are evaluated and compared against experimental values.

This paper presents the ongoing analysis of two fission experiments. Both projects are part of the collaboration between the nuclear reactions group at Uppsala and the JRC-IRMM. The first experiment deals with the prompt fission neutron multiplicity in the thermal neutron induced fission of U-235(n,f). The second, on the fission fragment properties in the thermal fission of U-234(n,f). The prompt fission neutron multiplicity has been measured at the JRC-IRMM using two liquid scintillators in coincidence with an ionization chamber. The first experimental campaign focused on U-235(nth,f) whereas a second experimental campaign is foreseen later for the same reaction at 5.5 MeV. The goal is to investigate how the so-called saw-tooth shape changes as a function of fragment mass and excitation energy. Some harsh experimental conditions were experienced due to the large radiation background. The solution to this will be discussed along with preliminary results. In addition, the analysis of thermal neutron induced fission of U-234(n,f) will be discussed. Currently analysis of data is ongoing, originally taken at the ILL reactor. The experiment is of particular interest since no measurement exist of the mass and energy distributions for this system at thermal energies. One main problem encountered during analysis was the huge background of U-235(nth, f). Despite the negligible isotopic traces in the sample, the cross section difference is enormous. Solution to this parasitic background will be highlighted.

The time-reversed reaction 15O(2p,γ)17Ne has been studied by the Coulomb dissociation technique. Secondary 17Ne ion beams at 500 AMeV have been produced by fragmentation reactions of 20Ne in a beryllium production target and dissociated on a secondary Pb target. The incoming beam and the reaction products have been identified with the kinematically complete LAND-R3B experimental setup at GSI. The excitation energy prior to decay has been reconstructed by using the invariant-mass method. The preliminary differential and integral Coulomb Dissociation cross sections (σCoul) have been calculated, which provide a photoabsorption (σphoto) and a radiative capture cross section (σcap). Additionally, important information about the nuclear structure of the 17Ne nucleus will be obtained. The analysis is in progress.

At the IGISOL-4 facility, neutron-rich, medium mass nuclei have usually been produced via charged particle-induced fission of natural uranium and thorium. Neutron-induced fission is expected to have a higher production cross section of the most neutron-rich species. Development of a neutron source along with a new ion guide continues to be one of the major goals since the commissioning of IGISOL-4. Neutron intensities at different angles from a beryllium neutron source have been measured in an on-line experiment with a 30 MeV proton beam. Recently, the new ion guide coupled to the neutron source has been tested as well. Details of the neutron source and ion guide design together with preliminary results from the first neutron-induced fission experiment at IGISOL-4 are presented in this report.

The fission product yields are an important characteristic of the fission process. In fundamental physics, knowledge of the yield distributions is needed to better understand the fission process. For nuclear energy applications good knowledge of neutron-induced fission-product yields is important for the safe and efficient operation of nuclear power plants. With the Ion Guide Isotope Separator On-Line (IGISOL) technique, products of nuclear reactions are stopped in a buffer gas and then extracted and separated by mass. Thanks to the high resolving power of the JYFLTRAP Penning trap, at University of Jyvaskyla, fission products can be isobarically separated, making it possible to measure relative independent fission yields. In some cases it is even possible to resolve isomeric states from the ground state, permitting measurements of isomeric yield ratios. So far the reactions U(p,f) and Th(p,f) have been studied using the IGISOL-JYFLTRAP facility. Recently, a neutron converter target has been developed utilizing the Be(p,xn) reaction. We here present the IGISOL-technique for fission yield measurements and some of the results from the measurements on proton induced fission. We also present the development of the neutron converter target, the characterization of the neutron field and the first tests with neutron-induced fission.

New experimental data for dissociation of relativistic 17Ne projectiles incident on targets of lead, carbon, and polyethylene targets at GSI are presented. Special attention is paid to the excitation and decay of narrow resonant states in 17Ne. Distributions of internal energy in the three-body system have been determined together with angular and partial-energy correlations between the decay products in different energy regions. The analysis was done using existing experimental data on 17Ne and its mirror nucleus 17N. The isobaric multiplet mass equation is used for assignment of observed resonances and their spins and parities. A combination of data from the heavy and light targets yielded cross sections and transition probabilities for the Coulomb excitations of the narrow resonant states. The resulting transition probabilities provide information relevant for a better understanding of the 17Ne structure.

This paper highlights some of the main activities related to fission of the nuclear reactions group at Uppsala University. The group is involved for instance in fission yield experiments at the IGISOL facility, cross-section measurements at the NFS facility, as well as fission dynamics studies at the IRMM JRC-EC. Moreover, work is ongoing on the Total Monte Carlo (TMC) methodology and on including the GEF fission code into the TALYS nuclear reaction code. Selected results from these projects are discussed.