It is difficult to underestimate the importance of neutron cross section standards in the nuclear data field. Accurate and precise standards are prerequisites for measuring neutron cross sections. Two different projects are presented here with the aim of improving on neutron standards. A simulation study was performed for an experiment intended to measure the cross sections of H(n,n), 235U(n,f), and 238U(n,f) relative to each other. It gave the first estimates of the performance of the experimental setup. Its results have aided the development of the experimental setup by setting limits on the target and detector design. A second neutron-standard project resulted in three measurements of 6Li(n,α)t relative to 235U(n,f). Each subsequent measurement improved upon the previous one and changed the experimental setup accordingly. Although, preliminary cross sections were agreeing well with evaluated data files in some energy intervals, the main goal to measure the cross section up to 3 MeV was not reached. Mass yields and energy spectra are important outcomes of many fission experiments, but in low yield regions the uncertainties are still high even for recurrently studied nuclei. In order to understand the fission dynamics, one also needs correlated fission data. One particular important property is the distribution of excitation energy between the two nascent fission fragments. It is closely connected to the prompt emission of neutrons and γ’s and reveals information about how nucleons and energy are transferred within the fissioning nucleus. By measuring both the pre and post neutron-emission fragment masses, the cumbrance of detecting neutrons directly is overcome. This is done using the fission spectrometer VERDI and the 2E-2v method. In this work I describe how both the spectrometer, the analysis method, and the calibration procedures have been further developed. Preliminary experimental data show the great potential of VERDI, but also areas that call for more attention. A previously overlooked consequence of a central assumption was found and a correction method is proposed that can correct previously obtained data as well. The last part of this thesis concerns the efficiencies of the fission product extraction at the IGISOL facility. The methodology of the fission yield measurements at IGISOL are reliant on assumptions that have not been systematically investigated. The presented work is a first step of such an investigation that can also be used as a tool for optimising the setup for measurements of exotic nuclei. A simulation framework connecting three different simulation codes was developed to investigate the produced yield of fission products in a buffer gas. Several different variants of the setup were simulated and the findings were generally accordant with previous estimates. A reasonable agreement between experimental data and the simulation results is demonstrated.

<p>Light-ions (protons, deuterons, tritons, ³He and α articles) production in the interaction of 175 MeV neutrons with iron and bismuth has been measured using the Medley setup at the The Svedberg Laboratory (TSL) in Uppsala. These measurements have been conducted in the frame of an international collaboration whose aim is to provide the scientific community with new nuclear data of interest for the development of Accelerator Driven Systems, in the range of 20 to 200 MeV. In this Licentiate Thesis I will present the background for the present experiment, the choice of the measured materials (iron and bismuth) and of the energy range. I will then give a short theoretical description of the involved nuclear reactions and of the model used to compare the experimental results. A description of the neutron facility at TSL and of Medley setup will follow. Monte Carlo simulations of the experimental setup have been performed and some results are here reported and discussed. I will present data reduction procedure and finally I will report preliminary double differential cross sections for production of hydrogen isotopes from iron and bismuth at several emission angles. Experimental data will be compared with model calculations with TALYS-1.0; these show better agreement for the production of protons, while seems to overestimate the experimental production of deuterons and tritons.</p>

Light-ions (protons, deuterons, tritons, 3He and α articles) production in the interaction of 175 MeV neutrons with iron and bismuth has been measured using the Medley setup at the The Svedberg Laboratory (TSL) in Uppsala. These measurements have been conducted in the frame of an international collaboration whose aim is to provide the scientific community with new nuclear data of interest for the development of Accelerator Driven Systems, in the range of 20 to 200 MeV. In this Licentiate Thesis I will present the background for the present experiment, the choice of the measured materials (iron and bismuth) and of the energy range. I will then give a short theoretical description of the involved nuclear reactions and of the model used to compare the experimental results. A description of the neutron facility at TSL and of Medley setup will follow. Monte Carlo simulations of the experimental setup have been performed and some results are here reported and discussed. I will present data reduction procedure and finally I will report preliminary double differential cross sections for production of hydrogen isotopes from iron and bismuth at several emission angles. Experimental data will be compared with model calculations with TALYS-1.0; these show better agreement for the production of protons, while seems to overestimate the experimental production of deuterons and tritons.

SCALP (Scintillating ionization Chamber for ALpha particle production in neutron induced reactions) est un dispositif expérimental conçu pour la mesure de la section efficace de la réaction O-16(n,alpha)C-13. Cette réaction fait partie de la HPRL (High Priority Request List) de la NEA. Elle est très importante pour la physique des réacteurs car la production d'hélium a des conséquences sur le fonctionnement des réacteurs électrogènes à neutrons thermiques et neutrons rapides.Les simulations Monte Carlo effectuées avec Geant4 montrent que le dispositif conçu (une chambre d'ionisation scintillante entourée de quatre photo-multiplicateurs) est apte à la mesure de la section efficace. Les sections efficaces des réactions O-16(n,alpha)C-13 et F-19(n,alpha)N-16 (réaction nucléaire étudiée pour la normalisation en section efficace) entre le seuil en énergie et 10MeV peuvent être mesurées expérimentalement avec une erreur relative minimale de 15%.Toutefois, il faudra en améliorer les performances pour obtenir de plus faibles incertitudes comme requis par la NEA : une mesure de la section efficace de la réaction O-16(n,alpha)C-13 avec une précision inférieure à 10%. / SCALP (Scintillating ionization Chamber for ALpha particle production in neutron induced reactions) is an experimental device conceived to measure the cross section of the n-induced reaction on oxygène O-16(n,alpha)C-13. This latter reaction belongs to the HPRL (High Priority Request List) NEA list and is relevant in reactor physics because of the helium production affecting important fast and thermal neutron reactor's parameters.The Monte Carlo simulations with Geant4 showed that the device (a scintillating ionization chamber surrounded by four photomultipliers tubes) can measure and discriminate the different reactions inside the scintillating ion chamber. Cross section of O-16(n,alpha)C-13 and F-19(n,alpha)N-16 (used for cross section normalisation) reactions between the energy threshold and 10MeV could be experimentally measured with a 15% relative accuracy. However some improvement will be necessary to obtain lower uncertainties as requested by the NEA : O-16(n,alpha)C-13 cross section measurement with a accuracy better than 10%.