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1
Claeys, François. « Mesure, modélisation et évaluation de sections efficaces à seuil (n, xnγ) d’intérêt pour les applications de l’énergie nucléaire ». Electronic Thesis or Diss., Strasbourg, 2023. http://www.theses.fr/2023STRAE027.
Texte intégralRésumé :
Dans le contexte du développement des réacteurs de génération IV, des données nucléaires précises sont requises. Dans ce travail de thèse, on s’intéresse en particulier à la section efficace de diffusion inélastique (n, n’) pour les noyaux d’233U et d’238U. L'analyse des données de GRAPhEME, dispositif combinant les méthodes de la spectroscopie-γ prompte et du temps de vol, ont permis d’obtenir, pour la première fois, 12 sections efficaces 233U(n, n’γ). Une modélisation des sections efficaces de ces deux isotopes (233U et 238U) a été réalisée avec le code de réaction nucléaire TALYS. Dans le cas de l’238U, l’implémentation de nouveaux modèles permet un meilleur accord calcul/mesure pour les sections efficaces (n, n’γ). Il a été montré cependant que cela n’influe pas sur la section efficace (n, n’). Enfin, une évaluation des incertitudes des sections efficaces de réaction pour l’238U menée avec CONRAD compare différentes méthodes afin de propager les incertitudes expérimentales aux paramètres des modèles via l’inférence BayésienneIn the context of the development of generation IV nuclear reactors, precise nuclear data are needed. In this work, we study in particular inelastic scattering cross section for 233U and 238U nuclei. From the analysis of data from GRAPhEME, an experimental device combining prompt γ- spectroscopy and time of flight, we obtained for the first time 12 233U(n, n’γ) reaction cross sections. Cross sections modelling has been performed for both isotopes (233U et 238U) with the nuclear reaction code TALYS. In the 238U case, the implementation of new model in the code highlighted better agreement calculation/experiment for (n, n’γ) reaction cross sections. Despite this result, no change in the total inelastic scattering cross section has been seen. Finally, a cross sections uncertainties evaluation has been done with CONRAD, comparing different methods of propagating experimental uncertainties to model parameters via the Bayesian inference
2
Uemura, Sho. « Differential cross section measurement for the d(n,np) reaction ». Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61004.
Texte intégralRésumé :
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 83-84).
The differential cross section for the quasielastic d(n,np) neutron-induced deuteron breakup reaction was measured as a function of incident and scattered particle energies and angles, using a liquid deuterium target at the Weapons Neutron Research (WNR) spallation neutron beam at the Los Alamos Neutron Science Center at the Los Alamos National Laboratory. Cross sections were computed for the incident neutron energy ranges of 10010, 20010, and 30010 MeV. We used proton detectors covering a range of = 17 - 25 in the lab frame, and neutron detectors covering a range of = 55 - 76 in the lab frame. Experiment setup and data analysis are discussed, and preliminary results are presented for the cross section.
by Sho Uemura.
S.B.
3
Sage, Christophe. « Total and (n,2n) neutron cross section measurements on 241Am ». Strasbourg, 2009. https://publication-theses.unistra.fr/public/theses_doctorat/2009/SAGE_Christophe_2009.pdf.
Texte intégralRésumé :
Des mesures de sections efficaces neutroniques sur l’241Am ont été réalisées à l’IRMM à Geel, en Belgique, dans le cadre d’une collaboration entre ce laboratoire de la Commission Européenne et des laboratoires français du CEA et du CNRS. Des échantillons d'oxyde d'américium spécialement dédiés à ces mesures furent fabriqués au sein de l'ITU à Karlsruhe à partir de matière première fournie par le CEA Marcoule. Concernant la mesure de la réaction (n,2n), les irradiations eurent lieu auprès de l'accélérateur Van de Graaff de l'IRMM en plusieurs sessions de février 2007 à mars 2008. Cet accélérateur fournit un faisceau de neutrons quasi-monoénergétiques à des énergies comprises entre 8. 4 et 20. 6 MeV via les réactions D(d,n)3He et T(d,n)4He. La section efficace fut déterminée relativement à celle de la réaction standard 27Al(n,α)24Na. Les résultats détaillés dans cette thèse présentent la première mesure expérimentale de cette section efficace au-delà de 15 MeV, ainsi que trois autres énergies en bon accord avec les expériences précédentes. Les mesures de sections efficaces totale et de capture furent effectuées au sein de la source blanche de neutrons GELINA de l'IRMM. Ces mesures, effectuées entre mars 2007 et décembre 2008, se concentrent principalement sur les deux premières résonances de la section efficace de l'241Am aux énergies 0. 3 et 0. 57 eV. Les résultats des mesures de transmission confirment les tendances des mesures intégrales vers une augmentation de la section efficace. Les mesures de capture furent effectuées dans la continuité de celles de transmission, mais leur analyse n'est pas incluse dans ce travail de thèseNeutron induced reaction cross sections on 241Am have been measured at the IRMM in Geel, Belgium, in the frame of a collaboration between the EC Joint Research Centres IRMM and ITU and French laboratories from CNRS and CEA. Raw material coming from the Atalante facility of CEA Marcoule has been transformed into suitable AmO2 samples embedded in Al2O3 and Y2O3 matrices. The irradiations for the 241Am(n,2n)240Am reaction cross section measurement were carried out at the 7 MV Van de Graaff accelerator using the activation technique with quasi mono-energetic neutrons from 8 to 21 MeV produced via the D(d,n)3He and the T(d,n)4He reactions. The cross section was determined relative to the 27Al(n,α)24Na standard cross section and was investigated for the first time above 15 MeV. The induced activity was measured off-line by standard γ-ray spectrometry using a high purity Ge detector. A special effort was made for the estimation of the uncertainties and the correlations between our experimental points. A different sample of the same isotope 241Am has been measured in transmission and capture experiments in the resolved resonance region at the neutron ToF facility GELINA. The transmission measurement was performed in two campaigns, with an upgrade of the whole data acquisition system in between, followed by an investigation of its new performances. A preliminary analysis of the resonance parameters tends to confirm the recent evaluation to a higher value for the cross section at the bottom of the first resonances. A new design of C6D6 detectors for capture measurements has been studied, but the data reduction and analysis of the measurement are not part of this work
4
Ralston, James. « The 10B(n, α) and 10B(n, p) Cross-Sections in the MeV Energy Range ». Ohio University Honors Tutorial College / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1315160730.
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Yang, Hongwei. « THE N-P SCATTERING CROSS SECTION FROM 90 KEV TO 1.8 MEV ». UKnowledge, 2015. http://uknowledge.uky.edu/physastron_etds/33.
Texte intégralRésumé :
There have been very few measurements of the total cross section for n-p scattering below 500 keV. In order to differentiate among NN potential models, improved cross section data between 20 and 600 keV are required. We measured the n-p and n-C total cross sections in this energy region by transmission; a collimated neutron beam was passed through CH2 and C samples and transmitted neutrons were detected by a BC-501A deuterated liquid scintillator. Cross sections were obtained by taking the ratios of normalized neutron yields with the samples in the beam and with no sample in the beam. Both better precision and larger range between 90 keV and 1.8 MeV results are presented. The parameters resulting from fitting effective range theory to the data for n-p scattering are in good agreement with parameters determined from previous fits.
6
CIANI, GIOVANNI FRANCESCO. « Cross section of the 13C(a,n)16O reaction at low energies ». Doctoral thesis, Gran Sasso Science Institute, 2019. http://hdl.handle.net/20.500.12571/9705.
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Jansson, Kaj. « Improving the Neutron Cross-section Standards 238U(n,f) and 6Li(n,a) : Measurements and Simulations ». Licentiate thesis, Uppsala universitet, Tillämpad kärnfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-255235.
Texte intégralRésumé :
Improving or extending the range of cross-section standards, which in general are believed to be well known, require good control of the experimental conditions and the uncertainties involved. Two experiments that aspire to improve two different neutron cross-section standards, 238U(n,f) and 6Li(n,a, are presented in this thesis. Both standards have previously been extensively measured, but outside certain energy ranges discrepancies exist. In this thesis, a future precision measurement of the 238U(n,f) standard, relative to the elastic neutron scattering on hydrogen, is analysed through simulations. The status of the currently ongoing measurement of the second standard, 6Li(n,a), is also reported and some preliminary results are presented.Measurements of the uranium standard, with a total uncertainty better than 2%, are planned at the upcoming NFS facility. The new experimental situation requires our existing setup to be upgraded with new detectors. The simulation study has supplied limits on the target and detector designs but also provided estimates of the uncertainties that show the feasibility of a precision measurement. The design of the whole setup and the development of new detectors are guided by the simulation study presented in this thesis. When the upgrade is complete, the setup will consist of two parallel plate avalanche counters (PPACs), in addition to the eight detector telescopes already present in the existing setup.The 6Li(n,a) measurement is ongoing at the GELINA facility at IRMM in Geel, Belgium. A twin Frisch-grid ionisation chamber is employed measuring both 6Li(n,a) and 235U(n,f) in separate compartments. Although a problematic background was found, the preliminary cross section in the resonance region around 240 keV reproduces evaluated neutron library data fairly well. A recent move of the setup to a position closer to the neutron production shows promising improvements in the background situation.
8
Wright, Tobias James. « High accuracy measurement of the 238U(n,γ) cross section at the CERN n_TOF facility ». Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/high-accuracy-measurement-of-the-238un-cross-section-at-the-cern-ntof-facility(53f5fd77-2dd7-4518-b0fa-ce0863ae0409).html.
Texte intégralRésumé :
The radiative capture cross section of a highly pure (99.999%), 6.125(2) grams 238U sample ((9.56±05)e-4 atoms/barn) has been measured in the 185 m flight path at the CERN neutron time-of-flight facility n_TOF in the energy range 0.3 eV-20 keV. The Total Absorption Calorimeter (TAC) detection system, an array of 40 BaF2 crystals, was used utilising the total absorption technique, where all the γ-rays from the capture cascades are detected. These data have undergone careful background subtraction, with special care being given to the background originating from neutrons scattered by the 238U sample. Pile-up and dead-time effects have been corrected for using an innovative correction method valid for variable high count rates within a complex detection system such as the TAC. The resulting capture yield has an uncertainty of up to 2.2% below 5 keV and up to 3.7% between 5 and 20 keV, in line with the accuracy requested in the NEA High Priority Request List. A resonance analysis has been performed up to 5 keV with the code SAMMY. Between 5 and 20 keV, the cross section is treated as unresolved and averaged. The results confirm the excellent quality of the most recent nuclear data evaluations within quoted uncertainties and suggest some improvements. In particular, these TAC data suggest a 2% increase in the average cross section in the energy range 2-9 keV and a 5% reduction in the energy range 9-20 keV.
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Fraval, Kevin. « Measurement and analysis of the 241 Am (n,γ) cross section at the Cern n _TOF facility ». Paris 7, 2013. http://www.theses.fr/2013PA077177.
Texte intégralRésumé :
La section efficace 241Am(n,gamma) a été mesurée auprès de l'installation n_TOF, au CERN par spectrometrie par temps de vol. Les détecteurs utilisés pour la-détection des photons étaient des scintillateurs liquide de type C6D6. Après calibration des détecteurs et sélection des évènements au delà d'un seuil de 300 keV en énergie déposée, les histogrammes extraits furent corrigés pour le temps mort et en efficacité via la méthode de fonction poids. Ces fonctions poids furent calculées par à l'aide de simulations numériques de la réponse des détecteurs effectuées avec MCNPX. Les différentes sources de bruit de fond furent estimées et normalisées afin d'être correctement soustraites du signal total. La rendement capture par l'échantillon fut ensuite calculé en divisant le taux net de comptage pondéré par le flux de neutrons incident et l'énergie d'excitation du noyau composé. Ce rendement fut ensuite normalisé au rendement de capture d'une résonance connue, nommément à 4. 9 eV sur l'isotope 197Au. Enfin, l'analyse des résonances avec le code SAMMY permit d'étendre le domaine résolu jusqu'à 320 eV, soit deux fois au delà des limites des précédentes évaluations. La section efficace thermique fut estimée à 678 +- 68 barns, et une analyse statistique des niveaux fut effectuée, ainsi qu'une analyse de la région non résolue, jusqu'à 150 keV. La section efficace moyenne entre 320 eV et 150 keV est supérieure aux précédentes estimations. De futurs travaux devront se concentrer sur la réduction du bruit de fond pour réduire l'incertitude sur la valeur thermique, et également la réduction de la sensibilité au flash gamma, afin d'étendre l'énergie maximale de la région non résolueThe 241Am(n,g) cross section was measured at the n_TOF facility, at CERN by time of flight spectrometry. The detectors used for photon detection were C6D6 liquid scintillators. After callbration and event selection above a 300 keV threshold, the extracted histograms were corrected for dead time an efficiency using the weighting function technique. These weighting functions were calculated using simulated detectors response obtained via MCPX. All the background sources were estimated and normalized for proper subtraction to the total signal. The sample's capture yield was then calculated by dividing the net weighted count rate by the incoming neutron flux and compound nucleus excitation energy. This yield was then normalized to the capture yield of a well know isotope, namely at 4. 9 eV on 197Au. Finally, resonance analysis performed with the SAMMY code allowed the extension of the resolved resonance range to 320 eV, which is twice larger than in previous evaluations. The thermal cross section was found to be 678 +- 68 barns, and a statistical analysis was performed, together with an unresolved region analysis, up to 150 keV. The average cross section between 320 eV and 150 keV is larger than in previous estimations. Future worl should focus on reducing background to minimize the uncertainty on the thermal value, and also reducing the sensitivity to the gamma flash, in order to extend the upper limit of the unresolved range
10
Brandenburg, Kristyn H. « Development of a Neutron Long Counter for (alpha,n) Cross Section Measurements at Ohio University ». Ohio University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1512730722722763.
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Vermeulen, Mark James. « Measurement of the ²³⁶U(n,γ) cross section for the thorium fuel cycle at the CERN n_TOF facility ». Thesis, University of York, 2015. http://etheses.whiterose.ac.uk/9681/.
Texte intégralRésumé :
This manuscript details the successful measurement, and subsequent analysis, of the uranium-236(n,g) radiative capture kernels in the resolved resonance region, of importance to the thorium fuel cycle. The experiment took advantage of the convenient features of the CERN n_TOF facility. Features such as a fully digital DAQ, high instantaneous neutron flux, and the powerful background rejection capabilities offered by the BaF2 Total Absorption Calorimeter (TAC) detector, owing to its near 4 pi solid angle coverage and high segmentation. These features, coupled with a high purity (99.85%) U-236 sample, resulted in the successful measurement of the radiative kernels to within 10%. Having successfully extracted the radiative kernels up to 1500 eV with the R-matrix code SAMMY, and accounted for all sources of uncertainty, is was possible to quantify the total uncertainty for the radiative kernels. In this manner, the uncertainties were found to range from 2.3%, for resonances with little scattering and pile-up, to 5.3% for resonances with more significant scattering and pile-up effects. Hence not only was the goal of achieving the requested accuracy of 10% achieved, but even reaching the desired 5%. Given the limited data available for this reaction, it is of value to be able to contribute the results of the current work to the nuclear data community to bolster the information currently available for the U-236 neutron capture cross section. Comparison with the latest versions of three of the major libraries, our cross section is in overall agreement with JEFF-3.2, 6% larger than JENDL-4.0 and 20% larger than ENDF/B-VII.1. These are sizable differences considering our accuracy of just 2-5%, suggesting that some revision of the libraries may be in order.
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Rodríguez, Marrero Ana Yaiza. « Measurement of the exclusive ([Ni][Mi subíndex][Ro] -> ; [Mi][- elevat][Ro][Pi][+ elevat]) and inclusive ([Ni][Mi subíndex] N -> ; [Mi][- elevat] N' [Pi][+ elevat]) single pion [Ni] interaction cross section in a carbon target using the SciBar detector at the K2K experiment ». Doctoral thesis, Universitat Autònoma de Barcelona, 2007. http://hdl.handle.net/10803/3392.
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Gilardy, Gwenaelle. « Measuring the 7Li(a ; g)11B reaction rate at temperatures relevant for the n-process ». Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0398/document.
Texte intégralRésumé :
L’étude des réaction (a,g) d’intérêt astrophysique est vaste. Ces réactions ont un rôle important dans la phase de fusion d’hélium des étoiles, dans la nucléosynthèse au moment du big bang ainsi que dans une grande partie des scénarios d'explosions stellaires. L’étude des réactions (a,g) impliquant des faisceaux stables peut être réalisée de diverse façon. Je me suis concentrée sur deux d'entre elles. La première est l’étude en cinématique directe en détectant les rayons gamma produits. C'est ce que j'ai fait durant ma thèse pour mesurer la section efficace de 7Li(a,g)11B. Cette réaction a été étudiée au cours des années pour différentes raisons en astrophysique nucléaire. Par exemple, il a été postule que cette réaction pourrait résoudre, au moment de la nucléosynthèse du big bang, le problème du Lithium. Il est clair, aujourd'hui, que ce n'est pas la solution, cependant, elle a un rôle dans la production de boron lors des supernovae de type Ic. Une autre façon d’étudier les réactions (a,g) est d'utiliser la cinématique inverse. L’idée est d'envoyer un faisceau d'ions lourd sur une cible d’hélium. Ce type de cinématique permet de détecter, avec une bonne efficacité, le noyau lourd de recul produit si le faisceau qui n'a pas interagit avec la cible, en est correctement séparé. Les séparateurs de masses, comme St. George, sont construit dans ce but. St. George sera impliquer dans la mesure de sections efficaces de réaction d’importance pour le processus s comme 16O(a,g)20NeThe study of (a,g) reactions of astrophysical interest is quite vast. These reactions play an important role in the quiescent Helium burning phase of stars, in big bang nucleosynthesis and in most explosive stellar scenarios. The studies of (a,g) reactions involving stable beams are performed in various ways. I have been concentrating on two of them. The first one is studying these reactions in direct kinematics by detecting the produced gamma rays. This is what I did during my thesis to measure the cross section of 7Li(a,g)11B. It has been studied throughout the years for several purposes in nuclear astrophysics. For example, it was postulated it could solve the big bang nucleosynthesis Lithium problem. Nowadays, it is clear it does not.However, this reaction plays a role in the production of Boron during type Ic Supernovae. Another way to study (a,g) reactions is to use inverse kinematics. The idea is to send a heavy element beam on a Helium target. This kind of kinematics allows for the detection, with good efficiency, of the heavy recoil product if the beam that did not interact in the target is properly separated. Recoil mass separators, like St. George, are built for this purpose. St. George will be involved in measuring cross sections of reaction important for the s-process like 16O(a,g)20Ne
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Warren, Justin N. « 35Cl(n,p) reactions in a 6Li enhanced CLYC detector ». Ohio University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1606843490983827.
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Lapinski, Felicia. « Experimental studies at CERN-nTOF of the 230Th(n,f) reaction ». Thesis, Uppsala universitet, Tillämpad kärnfysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-417867.
Texte intégralRésumé :
This work investigates the feasibility to perform an experiment at CERN n_TOF to study the fission cross section and fission fragment angular distribution (FFAD) of the 230Th(n,f) reaction. An analysis of fission fragment energy losses in the experimental target resulted in a choice of target thickness of 0.1 µm (100 µg/cm2 ), which yields good transmission out of the target at up to 45° emission angles from the target normal. A detection setup using ten PPAC detectors with nine thorium targets interleaved in between them was investigated, where the detectors and targets were tilted 45° with respect to the neutron beam. This makes it possible to measure all emission angles needed with respect to the neutron beam in order to determine the FFAD. For the experimental area EAR2 at n_TOF, a prediction of the count rate in the experiment resulted in low statistical uncertainties after a few weeks of beam time, which indicates that an experiment like this is feasible.Detta projekt undersöker genomförbarheten av ett experiment vid CERN n_TOF för att mäta tvärsnittet och fördelningen av emissionsvinklar av fissionsfragment (FFAD) från 230Th(n,f)-reaktionen. En analys av energiförlusterna av fissionsfragment inuti torium-provet resulterade i en optimal provtjocklek på 0.1 µm (100 µg/cm2 ), vilket medför att fissionsfragment som emitteras i vinklar upp till 45° från provets normal har hög sannolikhet att transmitteras ut ur provet. En detektionsuppställning med tio PPAC-detektorer med nio toriumprov mellan dem undersöktes, där detektorerna och proven antogs vara snedställda med 45° från neutronstrålens riktning. Detta möjliggör detektion av fissionsfragment i alla vinklar som är nödvändiga för att kunna mäta hela FFAD. För experimentanläggningen EAR2 vid n_TOF, resulterade en uppskattning av antalet detekterade fissionsevent per sekund i låga mätosäkerheter efter ett par veckor av mättid, vilket antyder att experimentet är görbart.
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Manna, Alice <1991>. « Measurement of the 235 U(n,f) cross section relative to the neutron-proton elastic scattering up to 500 MeV at n_TOF ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amsdottorato.unibo.it/9954/1/Manna_Alice_tesi.pdf.
Texte intégralRésumé :
Neutron cross-section standards are fundamental ingredients for both measurements and evaluations of neutron-induced reaction cross sections. This is the case of 235U(n,f)
cross section: one of the most important standard cross sections at thermal neutron energy and between 0.15 MeV and 200 MeV. Above 200 MeV this reaction plays an important role for several applications, from biological effectiveness, via nuclear astrophysics, to nuclear technology, as well as for fundamental nuclear physics.
However, no measurement exists for energies above 200 MeV. This led to a request for new absolute measurements of 235U(n,f) cross section, in order to extend the precision and possibly to establish it as a standard up to 1 GeV. The n_TOF facility at CERN offers the possibility to study such reaction thanks to the wide neutron energy spectrum available in its experimental area, from thermal to 1 GeV. A dedicated measurement campaign was carried out to provide accurate and precise cross-section data of the 235U(n,f) reaction in the energy region from 10 MeV to 500 MeV.
The experimental setup consisted of two chambers to detect the 235U fission events, while the neutron flux was simultaneously measured by exploiting the neutron-proton scattering process using three Proton Recoil Telescopes.
In this PhD thesis the development, implementation and characterisation of the two telescopes under the responsibility of the INFN are discussed, as well as the analysis of the data acquired during the campaign. In this measurement, the n_TOF neutron flux in the energy interval between 10 and 500 MeV was measured for the first time. In addition, the analysis of one of the two chambers dedicated to the measurement of fission events is presented in detail. From these data, the 235U(n,f) cross section was determined and represents, at this time, the unique measure of this
kind.
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Richard, Andrea L. « Measurement of the Breakup Cross Section of the D(d,n) Reaction at 6.94 MeV for the Active Interrogation of Hidden Fissile Materials ». Ohio University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1397479139.
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Massimi, Cristian <1980>. « Improved cross-section on n+197Au from high resolution time-of-flight measurements at n_TOF and GELINA : the road to a new standard ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/2098/1/cristian_massimi_tesi.pdf.
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Massimi, Cristian <1980>. « Improved cross-section on n+197Au from high resolution time-of-flight measurements at n_TOF and GELINA : the road to a new standard ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/2098/.
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Miller, Zachariah W. « A MEASUREMENT OF THE PROMPT FISSION NEUTRON ENERGY SPECTRUM FOR 235U(n,f) AND THE NEUTRON-INDUCED FISSION CROSS SECTION FOR 238U(n,f) ». UKnowledge, 2015. http://uknowledge.uky.edu/physastron_etds/29.
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Two measurements have been made, addressing gaps in knowledge for 235U(n,f) and 238U(n,f). The energy distribution for prompt fission neutrons is not well-understood below 1 MeV in 235U(n,f). To measure the 235U(n,f) prompt fission neutron distribution, a pulsed neutron beam at the WNR facility in Los Alamos National Laboratory was directed onto a 235U target with neutron detectors placed 1 m from the target. These neutron detectors were designed specifically for this experiment and employed a unique geometry of scintillating plastic material that was designed to reject backgrounds. Fission fragments were detected using an avalanche counter. Coincidences between fission fragment production and neutron detector events were analyzed, using a double time-of-flight technique to determine the energy of the prompt fission neutrons. A separate measurement was made, investigating the neutron-induced fission cross section for 238U(n,f). This measurement also used the pulsed neutron beam at the WNR facility. The neutron flux was normalized to the well-known hydrogen standard and the fission rate was observed for beam neutrons in the energy range of 130-300 MeV. Using an extrapolation technique, the energy dependence of the cross section was determined. These new data filled a sparsely populated energy region that was not well-studied and were measured relative to the hydrogen standard, unlike the majority of available data. These data can be used to constrain the fission cross section, which is considered a nuclear reaction standard.
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Tkáč, Matěj. « Úprava toku – Luha v Jeseníku n/Odrou ». Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2013. http://www.nusl.cz/ntk/nusl-226142.
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The object of this Master`s thesis is the river training of the Luha river in Jeseník nad Odrou. The thesis is divided into several chapters. In the theoretical introduction, the problems of the sediment flow regime are discussed. Moreover, it deals with the questions associated with the roughness in open channels and adjustment of riparian zones. As a part of the overall proposal of the flow adjustment, the hydraulically most suitable cross section in cunette is proposed. It is done with respect to the desired velocity ratios in the profile. Since the new cunette shape was established, the adjustment of vertical alignment was proposed. The thesis also contains the capacity assessment of the existing channel. Design of adjustment of flood protection measures includes mainly spatial rearrangement and increase the crest of levees with respect to the local conditions. The thesis also suggests the placement of vegetation in the riparian zones. Furhermore, the work deals with problems arising from the flow adjustment considering applicable laws and regulations of the Czech Republic. In the case of project implementation, it is necessary to evaluate these problems independently.
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Prokofiev, Alexander. « Nucleon-Induced Fission Cross Sections of Heavy Nuclei in the Intermediate Energy Region ». Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2001. http://publications.uu.se/theses/91-554-5009-1/.
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Pönitz, Erik. « Messung von Wirkungsquerschnitten für die Streuung von Neutronen im Energiebereich von 2 MeV bis 4 MeV mit der 15N(p,n)-Reaktion als Neutronenquelle ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-39906.
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In zukünftigen kerntechnischen Anlagen können die Materialien Blei und Bismut eine größere Rolle spielen als heute. Für die Planung dieser Anlagen werden verlässliche Wirkungsquerschnittsdaten benötigt. Insbesondere der Neutronentransport in einem Blei-Spallationstarget eines beschleunigergetriebenen unterkritischen Reaktors hängt stark von den inelastischen Streuquerschnitten im Energiebereich von 0,5 MeV bis 6 MeV ab. In den vergangenen 20 Jahren wurden elastische und inelastische Neutronenstreuquerschnitte mit hoher Präzision für eine Vielzahl von Elementen am PTB-Flugzeitspektrometer gemessen. Zur Erzeugung der Neutronen wurde hauptsächlich die D(d,n)-Reaktion genutzt. Aufgrund des Q-Wertes der Reaktion und der verfügbaren Deuteronenenergien können Neutronen im Energiebereich von 6 MeV bis 16 MeV erzeugt werden. Die Messung von Wirkungsquerschnitten bei niedrigeren Energien erfordert somit die Verwendung einer anderen neutronenerzeugenden Reaktion. Hierfür wurde die 15N(p,n)15O-Reaktion ausgewählt, da sie die Erzeugung monoenergetischer Neutronen bis zu einer Energie von 5,7 MeV erlaubt. In dieser Arbeit wird die 15N(p,n)-Reaktion auf ihre Eignung als Quelle monoenergetischer Neutronen in Streuexperimenten untersucht. Die Untersuchung der Reaktion beinhaltet die Messung von differentiellen Wirkungsquerschnitten für ausgewählte Energien und die Auswahl von optimalen Targetbedingungen. Differentielle elastische und inelastische Neutronenstreuquerschnitte wurden unter Anwendung der Flugzeitmethode für Blei bei vier Energien zwischen 2 MeV und 4 MeV gemessen. Eine Bleiprobe mit natürlicher Isotopenzusammensetzung wurde verwendet. Für den Nachweis der gestreuten Neutronen wurden NE213 Flüssigszintillatoren verwendet, deren Nachweiswahrscheinlichkeit gut bekannt ist. Winkelintegrierte Wirkungsquerschnitte wurden mit einem Legendre-Polynomfit unter Verwendung der Methode der kleinsten Quadrate bestimmt. Zusätzlich erfolgten Messungen für die isotopenreinen Streuproben 209Bi und 181Ta bei 4 MeV Neutronenenergie. Die Ergebnisse werden mit denen früherer Experimente und aktuellen Evaluationen verglichenIn future nuclear facilities, the materials lead and bismuth can play a more important role than in today’s nuclear reactors. Reliable cross section data are required for the design of those facilities. In particular the neutron transport in the lead spallation target of an Accelerator-Driven Subcritical Reactor strongly depends on the inelastic neutron scattering cross sections in the energy region from 0.5MeV to 6 MeV. In the recent 20 years, elastic and inelastic neutron scattering cross sections were measured with high precision for a variety of elements at the PTB time-of-flight spectrometer. The D(d,n) reaction was primarily used for the production of neutrons. Because of the Q value of the reaction and the available deuteron energies, neutrons in the energy range from 6MeV to 16MeV can be produced. For the cross section measurement at lower energies, however, another neutron producing reaction is required. The 15N(p,n)15O reaction was chosen, as it allows the production of monoenergetic neutrons with up to 5.7MeV energy. In this work, the 15N(p,n) reaction was studied with focus on the suitability as a source for monoenergetic neutrons in scattering experiments. This includes the measurement of differential cross sections for the neutron producing reaction and the choice of optimum target conditions. Differential elastic and inelastic neutron scattering cross sections were measured for lead at four energies in the region from 2MeV to 4MeV incident neutron energy using the time-offlight technique. A lead sample with natural isotopic composition was used. NE213 liquid scintillation detectors with well-known detection efficiencies were used for the detection of the scattered neutrons. Angle-integrated cross sections were determined by a Legendre polynomial expansion using least-squares methods. Additionally, measurements were carried out for isotopically pure 209Bi and 181Ta samples at 4MeV incident neutron energy. Results are compared with other measurements and recent evaluations
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Chang, Chih-Hsiang. « Proteomic studies on protein N-terminus and peptide ion mobility by nano-scale liquid chromatography/tandem mass spectrometry ». Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263596.
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Marble, Daniel Keith. « Fluorine K-Shell X-Ray Cross Section Measurements for ⁷Li, ¹⁰B, ¹²C, ¹⁴N, and ¹⁶O Ions on Ultra-Clean, Ultra-Thin Yf₃ Solid Target Foils ». Thesis, University of North Texas, 1991. https://digital.library.unt.edu/ark:/67531/metadc332734/.
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In this study, procedures were developed to produce ultra-clean, ultra-thin target foils and to remove x-ray interference from electron bremsstrahlung and low energy K-shell x-rays from contaminant elements.
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Galhaut, Bastien. « Etude de la mesure de la section efficace de la réaction 16O(n,alpha)¹³C du seuil à 10 MeV ». Thesis, Normandie, 2017. http://www.theses.fr/2017NORMC231/document.
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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%
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Hansson, Henrik. « Understanding interfaces in thin-film solar cells using photo electron spectroscopy. : Effect of post-deposition treatment on composition of the solar cell absorber ». Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-399623.
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The increasing demand of renewable energy is the big driving force for the research and development of more efficient solar energy conversion solutions. Solar cells, which use the photovoltaic effect to convert the photon energy to electrical current, are an important solar energy conversion technique. One solar cell technology is thin-film solar cells. Thin-film solar cells use an absorption layer with a direct band gap. A direct band gap has the advantage that the photons will penetrate less deep until a photoexcitation occur compared to semiconductors with an indirect band gap (e.g. silicon). For this reason the thin-film solar cells can be made very thin.CIGS is a common thin-film solar cell absorber material containing copper (Cu), indium (In), gallium (Ga) and selenium (Se). One objective of this work has been to determine element concentrations of CIGS absorption layers from sample measurements. The GGI ratio determines the band gap, which is an important factor for optimising the efficiency of the solar cell.1 The copper vacancy is the main acceptor dopant in CIGS. The Cu concentration has shown to be important for the efficiency and for other properties of the absorber [2].The measuring technique used in this work has been photoelectron spectroscopy (PES). PES produces a spectrum showing distinct peaks corresponding to electron binding energy levels for specific element subshells. Measurements with different photon energies have been performed on samples with and without post deposition treatment (PDT). A great deal of the effort has been to calculate relative element concentrations based on the PES peak intensities. Two important parameters when performing the calculations are the photoionization cross section (including the angular dependence of the cross section) and the inelastic mean free path of the photoelectrons.The results show that the GGI and the corresponding band gap will be almost the same with and without PDT except for close to the surface where PDT lowers the GGI.The calculations showed that the copper concentration is lowest at the surface. Moreover, PDT with RbF results in lower copper concentration closer to the junction.The results show a discrepancy of the GGI and CGI ratios when using the angular dependent cross sections in [10] and [11] compared to using the cross sections in [6] and [7].Det ökande behovet av förnybar energi gör att forskning och utveckling av solenergilösningar är av största vikt. Solceller, vilka utnyttjar den fotovoltaiska effekten, är den vanligaste tekniken för omvandling av solenergi till elektricitet. Tunnfilmssolceller är en typ av solceller vars absorbent har ett direkt bandgap, till skillnad från kisel som har ett indirekt bandgap. Fördelen med ett direkt bandgap är att det ljusabsorberande materialet kan göras mycket tunt.En vanlig tunnfilmssolcell är CIGS. Det är en komposit bestående av koppar (Cu), indium (In), gallium (Ga) och selen (Se). Ett syfte med detta självständiga arbete har varit att beräkna koncentrationerna av de ingående ämnena i halvledarskiktet av CIGS. GGI-kvoten bestämmer bandgapet, vilket är en viktig faktor för solcellens verkningsgrad. Kopparvakansen är den huvudsakliga halvledaracceptorn i CIGS. Kopparkoncentrationen har visat sig vara viktig för bl.a. solcellens verkningsgrad [2].Mättekniken som används i detta arbete kallas fotoelektronspektroskopi (PES). PES-mätningar ger ett spektrum där spektrallinjerna representerar olika nivåer av elektroners bindningsenergi för olika grundämnen. Mätningar med olika fotonenergier, på prover med och utan ytbehandling (PDT), har utförts. En stor del av arbetet har varit att beräkna relativa koncentrationer av de olika grundämnena från spektrallinjerna i spektrumet. Viktiga parametrar som man behöver ta hänsyn till i uträkningarna är sannolikheten för en fotoemissionsprocess hos fotonerna, vinkelberoendet och den fria medelväglängden hos fotoelektronerna.Resultaten visar att GGI-kvot och bandgap blir nästan detsamma med eller utan PDT, förutom närmast ytan där PDT minskar GGI-kvoten.Resultaten visar också att kopparkoncentrationen är lägst på ytan och att PDT med RbF minskar kopparkoncentrationen närmast ytan.Resultaten visar att det blir skillnader mellan GGI- och CGI-kvoterna beroende på om beräkningarna baserats på vinkelberoende träffytor enligt [10] och [11] eller baserats på träffytor enligt [6] och [7].
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Party, Eliot. « Etude des réactions (n, xn) pour les noyaux fertiles / fissiles du cycle du combustible innovant au Thorium ». Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAE020.
Texte intégralRésumé :
Pour atteindre les objectifs de précision des simulations de réacteurs, des données nucléaires précises sont nécessaires, particulièrement pour les futurs réacteurs. Dans ce travail de thèse, une étude approfondie des réactions (n,xn) sur le 232Th a été réalisée par la méthode de la spectroscopie gamma prompte associée a la technique du temps de vol. Les sections efficaces de 81 (n,n'γ), 11(n,2nγ) et 7 (n,3nγ) ont été obtenues pour des énergies de 0,2 a 20 MeV, ce qui étend considérablement la gamme d’énergie couverte par les données expérimentales. De plus, l'impact de l’incertitude des sections efficaces sur la simulation de systèmes nucléaires a été examiné pour les isotopes du cycle du thorium 232Th et 233U en utilisant les logiciels MCNP et SERPENT. Ce travail a montré que l’incertitude sur la section efficace de diffusion inélastique (n,n’) du 232Th est la source d’incertitude principale pour plusieurs paramètres de réacteurTo attain target precisions in reactor simulation, accurate nuclear data are needed, especially for future reactors. In this work, a thorough study of (n,xn) reactions on 232Th has been realised using prompt gamma spectroscopy associated with time of flight method. Cross sections of 81 (n,n'γ), 11 (n,2nγ) and 7 (n,3nγ) have been obtained for energies from 0,2 to 20 MeV, thus expanding considerably the energy range covered by experimental data. Moreover, the influence of cross sections’ uncertainties on nuclear system simulation has been studied for thorium fuel cycle isotopes 232Th and 233U using MCNP and SERPENT codes. This work has shown that uncertainty on inelastic scattering (n,n’) for 232Th is the main contributors to uncertainty of several reactor parameters
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Chetry, Taya Nath. « A Study of the Reaction γd → ϖ+ϖ- d (From Vector Mesons to Possible Dibaryons) ». Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1547590526890843.
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Júnior, Felisberto Alves Ferreira. « Medidas das seções de choque térmicas e integrais de ressonância das reações 34S(n,)35S e 42K(n,)43K - Aperfeiçoamento por simulação de Monte Carlo ». Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-13032013-103136/.
Texte intégralRésumé :
Amostras de nitrato de potássio e enxofre natural foram irradiadas no núcleo do reator de pesquisas IEA-R1 do Instituto de Pesquisas Energéticas e Nucleares, IPEN/CNEN-SP, operando entre 3,5 e 5 MW de potência, para determinar as secções de choque térmicas e integrais de ressonância das reações 34S(n,)35S e 42K(n,)43K. O fluxo de nêutrons foi monitorado com ligas ouro-alumínio. As atividades induzidas nos alvos de ouro-alumínio e nitrato de potássio foram medidas com um detector semicondutor de germânio hiper puro; as atividades dos alvos de enxofre foram determinadas com um sistema de coincidências 4\\pi\\beta - \\gamma. Os efeitos de depressão de fluxo, autoblindagem e autoabsorção nos alvos foram corrigidos com base em simulações com o método de Monte Carlo por meio do programa MCNP. O programa PENELOPE, também baseado no método de Monte Carlo, foi modificado para simular o comportamento do sistema de coincidências 4\\pi\\beta - \\gamma. O formalismo de Westcott e o método da razão de cádmio foram usados para determinar os fluxos de nêutrons térmicos e epitérmicos, assim como as secções de choque térmicas e integrais de ressonância de ambos nuclídeos. Foi efetuado um tratamento estatístico das incertezas envolvidas e determinadas as covariâncias entre os resultados, incluindo aquelas decorrentes das incertezas do padrão de referência (ouro). As reações 34S(n,)35S e 42K(n,)43K apresentaram, respectivamente, seções de choque térmicas de 228(14) mb e 44,8(9) b, e integrais de ressonância de 144(6) mb e 1635(75) b. Estes resultados são incompatíveis com aqueles obtidos com cálculos teóricos. A seção de choque térmica da reação 34S(n,)35S concorda com valores obtidos por outros autores, dentro das incertezas experimentais.Samples of potassium nitrate and natural sulphur were irradiated in the IPEN/CNEN-SP IEA-R1 research reactor core, operating between 3.5 and 5 MW, to determine the thermal neutron cross sections and resonance integrals of 34S(n,)35S and 42K(n,)43K reactions. The neutron flux was monitored with gold-aluminium alloy. The activities induced in targets of gold-aluminium and potassium nitrate were measured with a high purity germanium detector. Sulphur targets activities were determined with a 4\\pi\\beta-\\gamma coincidences system by the tracer method. Flux depression, self-shielding and self-absorption in the targets was evaluated by simulations using the MCNP software. The PENELOPE software, also based on Monte Carlo method, was modified to simulate the behavior of the 4\\pi\\beta-\\gamma coincidence system. The Westcott formalism and the cadmium ratio method were used to determine epithermal and thermal neutrons flux as well as the thermal cross sections and resonance integrals of both nuclides. A statistical analysis of the uncertainties was performed and the covariance between the results was determined, including those arising from the uncertainties of the gold reference standard. The results were compared with experimental values and theoretical predictions obtained by other authors. The 34S(n,)35S and 42K(n,)43K reactions had, respectively, thermal cross sections of 228(14) mb and 44.8(9) b, and integral resonances of 144(6) mb and 1635(75) b. These results are incompatible with the obtained with theoretical calculations. The 34S(n,)35S reaction thermal cross section agrees with values obtained by other authors, within the experimental uncertainties.
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Lamirand, Vincent. « Détermination de sections efficaces pour la production de champs neutroniques monoénergétiques de basse énergie ». Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00683170.
Texte intégralRésumé :
La réponse d'un détecteur de neutrons varie avec l'énergie du neutron incident. La détermination expérimentale de cette variation se réalise au moyen de champs neutroniques monoénergétiques. Ceux-ci sont produits par l'interaction entre un faisceau d'ions accélérés et une cible fine constituée d'un dépôt réactif sur un support métallique. En utilisant différentes réactions telles que 7Li(p,n), 3H(p,n), 2H(d,n) et 3H(d,n), il est possible de produire des neutrons entre 120 keV et 20 MeV dans la direction du faisceau incident (0°).Pour atteindre des énergies inférieures, il est possible d'augmenter l'angle du point de mesure par rapport à la direction du faisceau d'ions. Cependant, cette méthode présente des problèmes d'homogénéité en énergie et en fluence des neutrons à la surface du détecteur, ainsi qu'une augmentation de la proportion de neutrons diffusés. Une alternative est l'utilisation d'autres réactions nucléaires, notamment la réaction 45Sc(p,n) qui permet de descendre jusqu'à des énergies de 8 keV à 0°.Une étude complète de cette réaction et de sa section efficace a été menée au sein d'une coopération scientifique entre le laboratoire de métrologie et de dosimétrie des neutrons (LMDN) de l'IRSN, deux instituts de métrologie européens, le NPL (National Physical Laboratory, RU) et le PTB (Physikalisch-Technische Bundesanstalt, All), et l'IRMM (Institute for Reference Materials and Measurements, CEE). Parallèlement, d'autres réactions envisageables ont été étudiées : 65Cu(p,n), 51V(p,n), 57Fe(p,n), 49Ti(p,n), 53Cr(p,n) et 37Cl(p,n). Elles ont été comparées en termes d'émission neutronique et d'énergie minimale des neutrons produits.
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Júnior, Felisberto Alves Ferreira. « Medida da secção de choque térmica e da integral de ressonância da reação 41K(n,)42K ». Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-03112008-104617/.
Texte intégralRésumé :
Pastilhas de nitrato de potássio foram irradiadas no núcleo do reator de pesquisas IEA-R1m do Instituto de Pesquisas Energéticas e Nucleares, IPEN/CNEN-SP, operando a 2 MW de potência, para determinar a secção de choque térmica e integral de ressonância da reação 41K(n,g)42K. O fluxo de nêutrons foi monitorado com folhas de liga ouro-alumínio. As atividades induzidas nos alvos foram determinadas por espectroscopia gama com detectores de germânio hiper puro. Os cálculos realizados se basearam no formalismo de Westcott. Foram realizadas simulações com o código MCNP (Monte Carlo N-Particle) para determinar a auto-blindagem e a depressão do fluxo de nêutrons nas pastilhas durante as irradiações e os fatores de correção da eficiência de detecção para fontes volumétricas, que leva em conta a absorção de raios gama nas mesmas. Foi efetuado um tratamento estatístico das incertezas envolvidas e determinadas as covariâncias entre os resultados, incluindo aquelas decorrentes das incertezas do padrão de referência (ouro). Os resultados obtidos foram comparados com os de outros autores. Foi testada a possibilidade de se observar o produto da reação 41K(n,g)42K(n,g)43K.Pellets of potassium nitrate were irradiated in the IPEN/CNEN-SP (Instituto de Pesquisas Energeticas e Nucleares, Comissao de Energia Nuclear, Sao Paulo, SP) IEAR1m reactor core operating at 2 MW power in order to determine the 41K(n,g)42K reaction thermal cross-section and resonance integral. The neutron flux was monitored by Au-Al alloy foils, and the Westcott formalism was applied. Neutron self-shielding, flux depression and gamma-ray self-absorption in the relatively large samples, as well as the gamma-ray detection efficiency correction factor, were determined by simulation with MCNP code. The data reduction statistical methods included the determination of the covariances between the obtained results and the standard cross-sections used (Au). The results were compared to those already published. The observation of the consecutive neutron capture reaction leading to 43K was tried.
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Kleider, Jean-Paul. « Etude des centres profonds du silicium amorphe hydrogène a-Si:H par des mesures d'admittances de diodes Schottky : caractérisation d'interfaces SI ::(X)-N ::(1-X):H/A-SI:H sur des structures MIS ». Paris 6, 1987. http://www.theses.fr/1987PA066015.
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DDétermination des caractéristiques du silicium amorphe hydrogène par mesure et analyse des admittances de diodes Schottky fournies sur ce matériau: densité d'états en-dessous et au niveau de fermi avec section de capture efficace des électrons et énergie d'activation du matériel.
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Kessedjian, Grégoire. « Mesures de sections efficaces d'actinides mineurs d'intérêt pour la transmutation ». Thesis, Bordeaux 1, 2008. http://www.theses.fr/2008BOR13672/document.
Texte intégralRésumé :
Les réacteurs actuels produisent deux types de déchets dont la gestion et le devenir soulèvent des problèmes. Il s’agit d’abord de certains produits de fission et de noyaux lourds (isotopes de l’Américium et du Curium) au-delà de l’uranium appelés actinides mineurs. Deux options sont envisagées : le stockage en site géologique profond et/ou l’incinération de ces déchets dans un flux de neutrons rapides, c’est-à-dire, la transmutation par fission. Ces études font appel à de nombreuses données neutroniques. Malheureusement, les bases de données présentent encore de nombreuses insuffisances pour parvenir à des résultats fiables. L’objectif de ce travail est ici d’actualiser des données nucléaires et de les compléter. Nous avons ainsi mesuré la section efficace de fission de l’243Am (7370 ans) en référence à la diffusion élastique (n,p) afin de fournir des données indépendantes des mesures existantes dans la gamme des neutrons rapides (1 - 8 MeV). La réaction 243Am(n,f) a été analysée en utilisant un modèle statistique décrivant les voies de désexcitation du noyau composé d’244Am. Ainsi les sections efficaces de capture radiative (n,?) et de diffusion inélastique (n,n’) ont pu être évaluées. La mesure directe des sections efficaces neutroniques d’actinides mineurs constitue très souvent un véritable défi compte tenu de la forte activité des actinides mineurs. Pour cela, une méthode indirecte a été développée utilisant les réactions de transfert dans le but d’étudier certains isotopes du curium. Les réactions 243Am(3He,d)244Cm, 243Am(3He,t)243Cm et 243Am(3He,alpha)242Am nous ont permis de mesurer les probabilités de fission des noyaux de 243,244Cm et de l’242Am. Les sections efficaces de fission des curiums 242,243Cm(162,9 j, 28,5 ans) et de l’américium 241Am sont obtenues en multipliant ces probabilités par les sections efficaces calculées de formation des noyaux composés. Pour chaque mesure, une évaluation précise des erreurs a été réalisée à travers une étude des variances-covariances des résultats présentés. Pour les mesures de la réaction 243Am(n,f), une analyse des corrélations d’erreurs a permis d’interpréter la portée de ces mesures au sein des mesures existantesThe existing reactors produce two kinds of nuclear waste : the fission products and heavy nuclei beyond uranium called minor actinides (Americium and Curium isotopes). Two options are considered: storage in deep geological site and/or transmutation by fast neutron induced fission. These studies involve many neutron data. Unfortunately, these data bases have still many shortcomings to achieve reliable results. The aim of these measurements is to update nuclear data and complement them. We have measured the fission cross section of 243Am (7370y) in reference to the (n,p) elastic scattering to provide new data in a range of fast neutrons (1 - 8 MeV). A statistical model has been developed to describe the reaction 243Am(n,f). Moreover, the cross sections from the following reactions have been be extracted from these calculations: inelastic scattering 243Am(n,n’) and radiative capture 243Am(n,?) cross sections. The direct measurements of neutron cross sections are often a challenge considering the short half-lives of minor actinides. To overcome this problem, a surrogate method using transfer reactions has been used to study few isotopes of curium. The reactions 243Am(3He, d)244cm, 243Am(3He, t)243cm and 243Am(3He, alpha)242Am allowed to measure the fission probabilities of 243,244Cm and 242Am. The fission cross sections of 242,243Cm(162,9d, 28,5y) and 241Am(431y) have been obtained by multiplying these fission probabilities by the calculated compound nuclear neutron cross section relative to each channel. For each measurement, an accurate assessment of the errors was realized through variance-covariance studies. For measurements of the reaction 243Am(n,f), the analysis of error correlations allowed to interpret the scope of these measures within the existing measurements
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Michaud, Yonnel. « Etude phénoménologique de la réaction d'échange de charge (pi)-p -> ; (pi)[n à haute énergie] ». Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10097.
Texte intégralRésumé :
La presente these est consacree a l'etude de la reaction d'echange de charge pion negatif proton donne pion nul neutron. Cette reaction fait partie des processus quasi-elastiques, caracterises par de petits moments transferes, et donc non interpretables par la chromodynamique quantique. Le modele de glauber, utilise avec succes dans le cadre de la diffusion elastique, est exploite ici pour l'etude de la reaction d'echange de charge. Une interaction effective entre quarks, incluant un terme central et un terme spinorbite, est employee afin de rendre compte de l'echange du meson rho. Les resultats obtenus permettent de conclure a la nature diffractive de la reaction etudiee, mais ne permettent pas de determiner avec precision les rayons moyens des densites de quarks interagissants
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Domula, Alexander Robert. « Neutronenphysikalische Studien an Germanium für Experimente zum neutrinolosen Doppelbetazerfall von 76-Ge ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-132646.
Texte intégralRésumé :
Ein Ziel der modernen Physik ist die experimentelle Beobachtung des neutrinolosen Doppelbetazerfalls (0nbb). Unter den wenigen in der Natur vorkommenden Nukliden ist 76-Ge ein möglicher Kandidat an denen dieser Prozess unter anderem mit dem Experiment GERDA nachgewiesen werden soll. Die extrem geringe Wahrscheinlichkeit für das Auftreten einer 0nbb-Umwandlung ist mindestens zehn Größenordnungen kleiner ist als die des Beta-Zerfalls von 115-In mit einer Halbwertszeit von 4,41x10^14 Jahren, einem der seltensten in der Natur beobachteten Kernumwandlungen. Die dafür erforderliche hohe Detektions Sensitivität wird unter anderem vom Messuntergrund bestimmt, dessen genaue Kenntnis für die Auswertung der Messdaten erforderlich ist. In dieser Arbeit wurden neutronenphysikalische Studien an Germanium durchgeführt, die essentielle Lücken in diesem Kenntnisstand schließen. Neutronen können durch direkte Wechselwirkung mit Germanium sowie der umgebenden Materie des Detektors oder indirekt durch Aktivierung Zählereignisse hervorrufen. Für das Verständnis des damit verursachten Untergrundes wurde der Neutronenwechselwirkungsquerschnitt 70-Ge(n,3n)68-Ge, das Anregungsschema von 76-Ge und der energieabhängige Anregungsquerschnitt für einige dieser Zustände untersucht. Der mangelhafte Messdatenbestand für natürlich vorkommende Germaniumisotope wird dabei entscheidend verbessert. Um die Untersuchung des 76-Ge Anregungsschemas und den Zugang zu einer Palette weiterer Experimente zu ermöglichen, wurde im Rahmen dieser Arbeit ein leistungsfähiges, sehr speziellen Anforderungen entsprechendes Rohrpostsystem entwickelt und im Neutronenlabor der TU Dresden installiert. Ein weiteres neutronenphysikalisches Experiment untersucht den bisher unbeobachteten Elektroneneinfang von 76-As. Dadurch wird eine Möglichkeit gezeigt die oftmals nur mit theoretischen Modellen zugänglichen und mit großen Unsicherheiten behafteten Übergansmatrixelemente experimentell zu bestimmen. Diese spielen bei der Auswertung von Experimenten zum Doppelbetazerfall, insbesondere des Experimentes GERDA, eine entscheidende RolleOne goal of modern physics is the experimental observation of the neutrinoless double beta decay (0nbb). Among the few naturally occurring nuclides 76-Ge is one candidate to which this process is to verify, amongest others with the GERDA experiment. The extremely low probability of occurrence for a 0nbb-decay is of at least ten orders of magnitude smaller than that of the Beta-decay of 115-In, one of the rarest beta transitions observed in nature with a half-life of 4.41x10^14 years. Thefore a high detection sensitivity is required, wich depends among other things on the measuring background. Its exact knowledge is necessary for the evaluation of the measuring data. In this work neutron-physical studies were performed on germanium aiming to close the essential gaps in this state of knowledge. Neutrons can cause counting events by direct interaction with germanium and the surrounding matter of the detector or indirectly by activation of any of these materials. For understanding of those background signals, the neutron interaction cross section 70-Ge(n,3n)68-Ge, the levelsceme and the energy-dependent excitation cross section of 76-Ge has been investigated. The lack of data inventory for natural germanium has been improved significantly. To enable the investigation of the 76-Ge level sceme and the access to a range of other experiments, a powerful, very special requirements corresponding pneumatic tube system was developed and installed in scope of this work at the neutron laboratory of the TU Dresden. Another neutron physics experiment examined the so far unobserved electroncapture of 76-As. This shows one way to determine transition matrix elements experimentally, which is often only accessible through theoretical models and prone to large uncertainties. These Matrix elements play a crucial role in the analysis of experiments on double beta decay, in particular the GERDA experiment
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Lee, Hurng-Chun, et 李宏春. « Semiclassical close coupling calculation of the electron capture cross section for N^{4+} + H collisions ». Thesis, 1999. http://ndltd.ncl.edu.tw/handle/83124831432614584633.
Texte intégralRésumé :
碩士中原大學
物理學系
87
Due to the possible applications in astrophysics and plasma physics in recent years, ion-atom scattering problem has become one of the most interesting topics in atomic physics. For electron capture processes in N^{4+}-H scattering, there are only few up-to-date molecular orbital (MO) calculations and various structures of total cross sections are predicted by different theoretical calculations in low energy regime. To investigate the origin of discrepancies among the MO results, we make a careful calculation for total and partial cross sections of this scattering system with collision energies from 30 eV/amu to 3500 eV/amu by using a so-called "two center atomic orbital (TCAO) semiclassical close-coupling model". In view that two electron processes such as double capture and simultaneous projectile-core excitations are small, we employ the one-electron model in this calculation. The effective potential performed by inner core is modified by diatomic model potential which can predict the N^{3+} and H atomic bound energies precisely on individual atomic center. Two AO basis sets have been used to check the convergence of the calculation and the results show that the pseudo-orbitals are not important in the calculation. On the other hand, we also use a heuristic coulomb trajectory correction to account for the trajectory effect in low energy regime. By including the trajectory correction, our results are generally in agreement with the theoretical calculation by Shimakura et. al. [12] in 1992 and experimental data by Folkerts et. al. [4] in 1995. However, we do not reproduce the structures predicted by various MO results in low energy regime.
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Foster, Ryan Dean. « A measurement of the longitudinal spin-dependent total cross section difference, in the n-d system ». 2004. http://www.lib.ncsu.edu/theses/available/etd-07012004-161358/unrestricted/etd.pdf.
Texte intégral
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Berger, Michael Anthony. « Preliminary design of an experiment for the measurement of the ⁶⁵Cu (n,2n) ⁶⁴Cu and ⁶⁴Zn (n, p) ⁶⁴Cu cross section at [symbol for approximately equal to]14 MeV ». 1986. http://catalog.hathitrust.org/api/volumes/oclc/68787456.html.
Texte intégral
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Burianová, Nicola. « Měření účinných průřezů v reaktorovém spektru : 55Mn(n,2n), 90Zr(n,2n), 127I(n,2n) ». Master's thesis, 2018. http://www.nusl.cz/ntk/nusl-383144.
Texte intégralRésumé :
This diploma thesis deals with the validation of spectral average cross-sections (SACS) of 55 Mn(n,2n)54 Mn, 90 Zr(n,2n)89 Zr, 127 I(n,2n)126 I reactions in well-defined LR-0 reactor spectrum. The measurement of SACS for selected reactions is of high interest because they are used for the practical reactor dosimetry. Various experiments for description of neutron field in reactor and detector characterization, which are necessary for validation, are described. The spectral average cross-sections are derived from Net Peak Areas of irradiated samples measured using a semiconductor high purity germanium detector. Obtained result were compared with MCNP6 calculations using ENDF/B-VII.0, ENDF/B-VII.1, JEFF-3.1, JEFF-3.2, JENDL-3.3, JENDL-4, ROSFOND-2010, CENDL-3.1 and IRDFF nuclear data libraries. Notable discrepancies were found in 90 Zr(n,2n)89 Zr and 127 I(n,2n)126 I reactions. This thesis also contains a theoretical basis for the interaction of neutrons with matter.
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Lange, J. Brandon. « Determination of the cross section and matrix element for H([pi]⁺,[pi]⁺[̧pi]⁺)N near threshold : a preliminary analysis ». Thesis, 1992. http://hdl.handle.net/2429/3004.
Texte intégralRésumé :
The total cross section for the reaction π+p —>π+π+n was measured at incident π
kinetic energies of 184 and 200 MeV. The threshold value for the matrix element
|a(π+π+)| was also determined through a preliminary analysis. The results are thus far
in disagreement with the world's data set and suggestions for further work have been
made.
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Domula, Alexander Robert. « Neutronenphysikalische Studien an Germanium für Experimente zum neutrinolosen Doppelbetazerfall von 76-Ge ». Doctoral thesis, 2013. https://tud.qucosa.de/id/qucosa%3A27463.
Texte intégralRésumé :
Ein Ziel der modernen Physik ist die experimentelle Beobachtung des neutrinolosen Doppelbetazerfalls (0nbb). Unter den wenigen in der Natur vorkommenden Nukliden ist 76-Ge ein möglicher Kandidat an denen dieser Prozess unter anderem mit dem Experiment GERDA nachgewiesen werden soll. Die extrem geringe Wahrscheinlichkeit für das Auftreten einer 0nbb-Umwandlung ist mindestens zehn Größenordnungen kleiner ist als die des Beta-Zerfalls von 115-In mit einer Halbwertszeit von 4,41x10^14 Jahren, einem der seltensten in der Natur beobachteten Kernumwandlungen. Die dafür erforderliche hohe Detektions Sensitivität wird unter anderem vom Messuntergrund bestimmt, dessen genaue Kenntnis für die Auswertung der Messdaten erforderlich ist. In dieser Arbeit wurden neutronenphysikalische Studien an Germanium durchgeführt, die essentielle Lücken in diesem Kenntnisstand schließen.
Neutronen können durch direkte Wechselwirkung mit Germanium sowie der umgebenden Materie des Detektors oder indirekt durch Aktivierung Zählereignisse hervorrufen. Für das Verständnis des damit verursachten Untergrundes wurde der Neutronenwechselwirkungsquerschnitt 70-Ge(n,3n)68-Ge, das Anregungsschema von 76-Ge und der energieabhängige Anregungsquerschnitt für einige dieser Zustände untersucht. Der mangelhafte Messdatenbestand für natürlich vorkommende Germaniumisotope wird dabei entscheidend verbessert.
Um die Untersuchung des 76-Ge Anregungsschemas und den Zugang zu einer Palette weiterer Experimente zu ermöglichen, wurde im Rahmen dieser Arbeit ein leistungsfähiges, sehr speziellen Anforderungen entsprechendes Rohrpostsystem entwickelt und im Neutronenlabor der TU Dresden installiert.
Ein weiteres neutronenphysikalisches Experiment untersucht den bisher unbeobachteten Elektroneneinfang von 76-As. Dadurch wird eine Möglichkeit gezeigt die oftmals nur mit theoretischen Modellen zugänglichen und mit großen Unsicherheiten behafteten Übergansmatrixelemente experimentell zu bestimmen. Diese spielen bei der Auswertung von Experimenten zum Doppelbetazerfall, insbesondere des Experimentes GERDA, eine entscheidende Rolle.One goal of modern physics is the experimental observation of the neutrinoless double beta decay (0nbb). Among the few naturally occurring nuclides 76-Ge is one candidate to which this process is to verify, amongest others with the GERDA experiment. The extremely low probability of occurrence for a 0nbb-decay is of at least ten orders of magnitude smaller than that of the Beta-decay of 115-In, one of the rarest beta transitions observed in nature with a half-life of 4.41x10^14 years. Thefore a high detection sensitivity is required, wich depends among other things on the measuring background. Its exact knowledge is necessary for the evaluation of the measuring data. In this work neutron-physical studies were performed on germanium aiming to close the essential gaps in this state of knowledge. Neutrons can cause counting events by direct interaction with germanium and the surrounding matter of the detector or indirectly by activation of any of these materials. For understanding of those background signals, the neutron interaction cross section 70-Ge(n,3n)68-Ge, the levelsceme and the energy-dependent excitation cross section of 76-Ge has been investigated. The lack of data inventory for natural germanium has been improved significantly. To enable the investigation of the 76-Ge level sceme and the access to a range of other experiments, a powerful, very special requirements corresponding pneumatic tube system was developed and installed in scope of this work at the neutron laboratory of the TU Dresden. Another neutron physics experiment examined the so far unobserved electroncapture of 76-As. This shows one way to determine transition matrix elements experimentally, which is often only accessible through theoretical models and prone to large uncertainties. These Matrix elements play a crucial role in the analysis of experiments on double beta decay, in particular the GERDA experiment.