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We have measured fission fragment-mass yields for neutron-induced fission of Th232 and U238 at energies 32.8, 45.3, and 59.9 MeV. The experiments were done at quasimonoenergetic neutron beams of the Cyclotron Research Center at Louvain-la-Neuve. To detect the fission fragments, a multisection Frisch-gridded ionization chamber was used. The measurement and data analysis techniques are discussed in detail. The obtained mass yields are compared to model calculations with the intermediate-energy nuclear reaction code MCFX. The MCFX code is used to calculate the fraction of fissioning nuclei after cascade, preequilibrium, and statistical reaction stages. The formation of mass distributions is considered as a result of oscillations of the mass-asymmetry degree of freedom in the potential well calculated with the temperature-dependent shell correction method. The experimental results as well as the results of the model calculations demonstrate that the probability of symmetric fission increases with incident neutron energy for both nuclei. The comparison also shows that the symmetric fission is more enhanced for thorium than for uranium with increasing neutron energy. We also compare U238 results with available experimental data; the Th232 data were measured for the first time. © 2011 American Physical Society.

Well-characterized neutron fields are a prerequisite for the investigation of neutron detectors. Partly in collaboration with external partners, the PTB neutron metrology group makes available for other users neutron reference fields covering the full energy range from thermal to 200 MeV. The specification of the neutron fluence in these beams is traceable to primary standard cross sections., Anglais

Fragment mass distributions from neutron-induced fission of /sup 232/Th and /sup 238/U have been measured at quasi-monoenergetic neutron beam of the Louvain-la-Neuve cyclotron facility CYCLONE. The measurements have been carried out making use of a multi-section Frisch-gridded ionization chamber. The measurement technique as well as the data processing is described. Preliminary data on primary fragment mass yields are given for an incident neutron energy of 32.8 MeV., Anglais

The cross sections for neutron induced fission of /sup 235/U, /sup 238/U, /sup 209/Bi and /sup nat/Pb were measured in the energy range from 30 MeV to 200 MeV using parallel-plate ionization chambers. Proton recoil telescopes and a /sup 238/U ionization chamber were employed for the determination of the incident neutron fluence. With the exception of a few deviating data points, the experimental results for /sup 235/U(n,f), /sup 238/U(n,f) and /sup 209/Bi(n,f) are close to the recommended cross sections., Anglais

We present an evaluation of the cross section for the reaction C-12(n,X)Be-7. This reaction is relevant to the formation of cosmogenic background in low-energy real time solar neutrino detectors employing carbon-based scintillators. We measured this cross section by using a quasi-monoenergetic (max. 63MeV) neutron beam at the Centre de Recherches du Cyclotron at Louvain-la-neuve: the produced Be-7 nuclei were detected by means of low background germanium gamma spectroscopy at the Laboratori Nazionali del Gran Sasso (LNGS). (C) 2008 Elsevier Ltd. All rights reserved.

The cross sections for neutron-induced fission of U-235, U-238, Bi-209, and Pb-nat in the intermediate energy region were measured using parallel plate fission ionization chambers. The experiments were carried out relative to the differential n-p scattering cross section using quasi-monoenergetic neutron beams with peak energies ranging from 33 to 200 MeV The experimental cross sections were compared to International Nuclear Data Committee reference fission cross sections, to results of nuclear model calculations, and to cross sections calculated with the nuclear models implemented in the radiation transport code MCNPX. The experimental results for U-235 and Bi-209 are consistent with the available reference cross sections and theoretical data while the U-238(n,f) cross section exceeds the reference cross section systematically by similar to 7% between 30 and 60 MeV The experimental resultsfor Pb-nat agree with a parameterization of other experimental data for Pb-nat(n,f).

Neutron-induced fission cross-sections of Tl-205, Pb-204,Pb-206,Pb-207,Pb-208 and Bi-209 have been measured in the energy range from 30 to 180 MeV. The measurements were performed with quasi-monoenergetic neutron beams using a multi-section Frisch-gridded ionization chamber. The neutron-induced fission cross-sections of U-238 were used as reference data. The experimental techniques are described in detail as well as the data processing. The results are compared with existing experimental data. (c) 2006 Elsevier B.V. All rights reserved.

Cette dissertation présente les résultats des mesures des sections efficaces inclusives de production des particules chargées légères (protons, deutons, tritons, 3He, alpha, 6Li, 7Li et 7Be) ainsi que les multiplicités neutroniques associées, relevés lors des réactions nucléaires induites par protons et alpha sur une cible de natSi. Ces mesures ont été réalisées auprès du cyclotron CYCLONE de Louvain-la-Neuve aux énergies de 26.5, 48.5 et 62.9 MeV pour les réactions (p, (nat)Si) et de 25.4, 45.5 et 57.8 MeV pour les réactions (alpha, (nat)Si). Le système de détection, original dans sa conception, a été assuré par 15 télescopes constitués d'un assemblage de jonctions silicium et de scintillateurs inorganiques CsI assurant une couverture angulaire de 0 à 360°. Toutes les particules chargées étudiées dans ce travail ont été identifiées sur base de l'information de leurs pertes d'énergie dans les différentes jonctions et par la technique de l'analyse en forme des signaux lumineux issus des CsI. La détection des neutrons a été assurée par le multi-détecteur à neutrons DEMON constitué de 81 scintillateurs organiques liquides. Ces neutrons ont été identifiés par la technique de l'analyse en forme du signal lumineux. L'énergie des neutrons a été déduite par mesure de leur temps de vol. Les distributions angulaires des pics élastiques et inélastiques de la diffusion des protons et des alpha sur le 28Si ont été confrontées aux prédictions des modèles Optique, DWBA et Canaux Couplés, utilisant différents potentiels optiques. Une comparaison des résultats expérimentaux avec ceux déjà publiés sur des réactions similaires ou comparables a également fait l'objet de ce travail. De plus, les résultats ont été confrontés à ceux des prédictions des codes de simulation GNASH et TALYS. Une attention particulière a été portée aux prédictions du code TALYS. Enfin, ce travail fournit une très large et très complète base de nouvelles données expérimentales qui constitue un atout majeur et b, (PHYS 3)--UCL, 2005

The production of dicentric chromosomes in human lymphocytes by high-energy neutron radiation was studied using a quasi-monoenergetic 60 MeV neutron beam. The average yield coefficient (alpha) over bar of the linear dose-response relationship for dicentric chromosomes was measured to be (0.146 +/- 0.016) Gy(-1). This confirms our earlier observations that above 400 keV, the yield of dicentric chromosomes decreases with increasing neutron energy. Using the linear-quadratic dose-response relationship for dicentric chromosomes established in blood of the same donor for Co-60 gamma-rays as a reference radiation, an average maximum low-dose RBE (RBEM) of 14 +/- 4 for 60 MeV quasi-monoenergetic neutrons with a dose-weighted average energy (E) over bar of 41.0 MeV is obtained. A correction procedure was applied, to account for the low-energy continuum of the quasi-monoenergetic spectral neutron distribution, and the yield coefficient alpha for 60 MeV neutrons was determined from the measured average yield coefficient (alpha) over bar. For alpha, value of (0.115 +/- 0.026) Gy(-1) was obtained corresponding to an RBEM of 11 +/- 4. The present experiments extend earlier investigations with monoenergetic neutrons to higher energies.

Les spectres énergétiques (sections efficaces doublement différentielles) de production de protons, deutons, tritons et particules alpha induite par des neutrons rapides sur 209Bi et natU sont présentées pour plusieurs énergies de neutrons incidents comprises entre 25 et 65 MeV. Les spectres ont été obtenus à 9 angles laboratoire entre 20° et 160° et extrapolés et interpolés à 10 autres angles afin de couvrir le domaine angulaire de 0 à 180°. Le dispositif expérimental et les procédures d'analyse des données incluant les corrections et la normalisation sont présentées et discutées. Sur base des sections efficaces doublement différentielles obtenues, les sections efficaces différentielles en énergie et en angle ainsi que les sections efficaces totales de production et les coefficients KERMA partiels associés sont également déduits. La thèse présente également des comparaisons aux rares mesures existantes dans la littérature ainsi qu'aux calculs théoriques basés sur les codes de réactions nucléaires INCL3, GNASH et TALYS. Tandis que l'INCL3 se base sur la cascade intranucléaire, les deux autres codes intègrent le modèle optique et les modèles de réactions directes, de prééquilibre, de fission et de noyaux composés dans un unique schéma de calcul. Finalement, sur base de l'ensemble des résultats obtenus depuis une dizaine d'années par le groupe, une vue nouvelle des sections efficaces totales de production et des coefficients KERMA partiels en fonction de la masse de la cible est proposée., (PHYS 3) -- UCL, 2004

Double-differential cross sections (energy spectra) for proton, deuteron, triton and alpha-particle emission in fast neutron-induced reactions on iron are reported for ten incident neutron energies between 25 and 65 Mev Energy spectra were obtained at nine laboratory angles between 20degrees and 160degrees and extrapolated or interpolated to ten other angles extending the angular distribution from 2.5degrees to 177.5degrees. The experimental set-up and the procedure for data taking and data reduction are briefly presented. Deduced energy-differential and total cross sections are also reported. Experimental cross sections are compared with data from proton-induced reactions on Fe-54 and Fe-56, and with our data from neutron-induced reactions on cobalt. Theoretical calculations of GNASH and TALYS reaction codes are also compared to the experimental data.

Well-characterised neutron fields are a prerequisite for the investigation of neutron detectors. Partly in collaboration with external partners, the PTB neutron metrology group makes available for other users neutron reference fields covering the full energy range from thermal to 200 MeV. The specification of the neutron fluence in these beams is traceable to primary standard cross sections.

We have measured cross sections of neutron-induced nuclear reactions leading to the delayed production of γ-ray lines similar to the ones of astrophysical interest. Conclusions were drawn concerning the expected background in the 26Al 1809 keV line and the 7Be 478 keV line in SPI. The neutron-induced degradation of Ge detectors was studied vs. the neutron energy, the neutron fluence and the detector temperature. Performance recovery of the detectors was studied for different annealing temperatures. Optimum temperature and times for annealing were determined., SCOPUS: ar.j, info:eu-repo/semantics/published

The principal goal of this thesis is to highlight a possible "neutron skin" effect in the nuclear reaction mechanisms between heavy ions at energies around 6 MeV/nucleon. To this end, the reactions 58Ni+122Sn at 354 and 375.5 MeV and 64Ni+116Sn at 382.5 MeV were carried out at the CYCLONE accelerator in Louvain-la-Neuve. The projectile Ni and the target Sn were selected because of their magicity in proton. This characteristic implies the existence of a proton core more bound and of a neutron peripheral distribution in the isotopes 64Ni and 122Sn, rich in neutrons. The first goal was, to observe the possible influence of these neutrons on the fusion probability between the projectile and the target. In addition, the two types of reactions were selected in order to produce the same compound nucleus (180Pt) with the same excitation energy or with the same angular momentum. Thus, the effect of a neutron skin could be observed from the point of view of the production as from the point of view of the de-excitation of the compound nucleus. This de-excitation can proceed by evaporation of light particles or by fission. So, on the one hand, the fusion, fusion-evaporation and fusion-fission cross sections, and, on the other hand, the multiplicities of the light particles (neutrons, protons or alpha) emitted by the compound nucleus or by the fission fragments should have been compared. The experimental realization of this project required the use of the neutron detection system DEMON made up of 90 liquid scintillators laid out on a 4 m in diameter sphere which contain an aluminium chamber under vacuum. The chamber contained two multi-wire proportionnal counters XY intended for the detection of the fission fragments, two systems of Silicon junctions coupled with microchannels intended for the detection of evaporation residues and finally six triple Silicon telescope intended for the detection of the light charged particles (protons and alpha). At the end of the analysis, it was, L'objectif principal de cette thèse est de mettre en évidence un éventuel effet de "peau de neutrons" dans les mécanismes des réactions nucléaires entre ions lourds à des énergies de l'ordre de 6 MeV/nucléon. Dans ce but, les réactions 58Ni+122Sn à 354 et à 375.5 MeV et 64Ni+116Sn à 382.5 MeV ont été réalisées auprès de l'accélérateur CYCLONE de Louvain-la-Neuve. Le projectile Ni et la cible Sn ont été choisis en raison de leur magicité en proton. Cette caractéristique implique l'existence d'un coeur de protons plus liés et d'une distribution plus périphérique des neutrons dans les isotopes 64Ni et 122Sn, riche en neutrons. Il s'agissait donc, dans un premier temps, d'observer l'influence possible de ces neutrons excédentaires sur la probabilité de fusion du projectile et de la cible. D'autre part, les deux types de réactions ont été choisis afin de produire le même noyau composé 180Pt de même énergie d'excitation ou de même moment angulaire. Ainsi, l'effet de peau de neutrons pouvait être observé tant du point de vue de la production que du point de vue de la désexcitation du noyau composé. Cette désexcitation peut se faire par évaporation de particules légères ou par fission. Plus précisement, il s'agissait de comparer, d'une part, les sections efficaces de fusion, de fusion-évaporation et de fusion-fission, et, d'autre part, les multiplicités des particules légères (neutrons, protons ou alpha) émises par le noyau composé ou les fragments de fission. La réalisation expérimentale de ce projet a nécessité l'utilisation du système de détection de neutrons DEMON constitué de 90 scintillateurs liquides disposés sur une sphère de 4 m de diamètre au centre de laquelle une chambre en aluminium était mise sous vide. Celle-ci contenait deux chambres à gaz et à multi-fils XY destinés à la détection des fragments de fission, deux systèmes de jonctions au Silicium couplées à des galettes à micro-canaux destinés à la détection de résidus d'évaporation et enfin six triple-télésc, (PHYS 3)--UCL, 2003

Energy spectra (double-differential cross sections) for proton, deuteron, triton, and alpha-particle production in fast neutron induced reactions on uranium are reported for several incident neutron energies between 25 and 65 MeV. The spectra were obtained at nine laboratory angles between 20degrees and 160degrees and extrapolated and interpolated to other ten angles suitably covering the laboratory angular domain of 0degrees to 180degrees. The experimental setup and procedures for data reduction including corrections and normalization are presented and discussed. Based on the obtained double-differential cross sections, energy-differential and total cross sections are deduced as well. Theoretical calculations are based on GNASH and TALYS nuclear reaction codes which integrate the optical model, direct, preequilibrium, fission, and statistical nuclear reaction models in one calculation scheme.

Experimental results concerning light charged particle (proton, deuteron, triton and alpha-particle) production in fast neutron induced reactions on bismuth are reported for several incident neutron energies between 25 and 65 MeV. Energy spectra (double-differential cross sections) were measured at 9 laboratory angles between 20degrees and 160degrees and extrapolated and interpolated to other 10 angles. The experimental set-up and procedures for data reduction including corrections and normalisation are shortly presented and discussed. Resulting energy-differential and total cross sections are reported as well. Experimental cross sections are compared to similar available data from neutron and proton induced reactions. Theoretical calculations are based on GNASH and TALYS nuclear reaction codes which integrate the optical model, direct, pre-equilibrium, fission and statistical nuclear reaction models in one calculation scheme. (C) 2003 Elsevier B.V. All rights reserved.

We have measured cross sections of neutron-induced nuclear reactions leading to the delayed production of gamma-ray lines similar to the ones of astrophysical interest. Conclusions were drawn concerning the expected background in the Al-26 1809 keV line and the Be-7 478 keV line in SPI. The neutron-induced degradation of Ge detectors was studied vs. the neutron energy, the neutron fluence and the detector temperature. Performance recovery of the detectors was studied for different annealing temperatures. Optimum temperature and times for annealing were determined.

Double-differential cross sections (energy spectra) for the proton, deuteron, triton and alpha-particle production in fast neutron induced reactions on cobalt are reported for ten incident neutron energies between 25 and 65 MeV. Energy spectra were obtained at nine laboratory angles between 20degrees and 160degrees and extrapolated or interpolated to other ten angles covering uniformly the laboratory angular domain of 0degrees to 180degrees. The experimental set-up and procedures for data reduction including corrections and normalization are presented and discussed. Based on the measured double-differential cross sections, energy-differential and total cross sections are reported as well. Experimental cross sections are compared with similar available data from neutron- and proton-induced reactions. Theoretical calculations based on semiclassical exciton model and Hauser-Feshbach statistical theory (GNASH code) and intranuclear cascade model for nucleon-induced interactions (INCL3 code) were done and compared to the experimental results.

Quasi-monoenergetic reference neutron beams in the energy range between 20 and 100 MeV have been produced and characterized with a proton recoil telescope, a scintillation spectrometer, a U-238 fission chamber and a Bonner sphere spectrometer. The beams are well suited for the calibration of detectors used in neutron spectrometry. A new method is described which reduces the correction for the contribution from low-energy neutrons present in the beams. (C) 2002 Elsevier Science B.V. All rights reserved.

In radiotherapy with external beams, healthy tissues surrounding the target volumes are inevitably irradiated. In the case of neutron therapy, the estimation of dose to the organs surrounding the target volume is particularly challenging, because of the varying contributions from primary and secondary neutrons and photons of different energies. The neutron doses to tissues surrounding the target volume at the Louvain-la-Neuve (LLN) facility were investigated in this work. At LLN, primary neutrons have a broad spectrum with a mean energy of about 30 MeV. The transport of a 10 x 10 cm(2) beam through a water phantom was simulated by means of the Monte Carlo code MCNPX. Distributions of energy-differential values of neutron fluence, kerma and kerma equivalent were estimated at different locations in a water phantom. The evolution of neutron dose and dose equivalent inside the phantom was deduced. Measurements of absorbed dose and of dose equivalent were then carried out in a water phantom using an ionization chamber and superheated drop detectors (SDDs). On the beam axis, the calculations agreed well with the ionization chamber data, but disagreed significantly from the SDD data due to the detector's under-response to neutrons above 20 MeV. Off the beam axis, the calculated absorbed doses were significantly lower than the ionization chamber readings, since gamma fields were not accounted for. The calculated data are doses from neutron-induced charge particles, and these agreed with the values measured by the photon-insensitive SDDs. When exposed to the degraded spectra off the beam axis, the SDD offered reliable estimates of the neutron dose equivalent. (C) 2002 Elsevier Science B.V. All rights reserved.

Double-differential cross sections (energy spectra) for the proton, deuteron, triton and alpha -particle production in fast neutron induced reactions on cobalt are reported for ten incident neutron energies between 25 and 65 MeV. Energy spectra were obtained at nine laboratory angles between 20 degrees and 160 degrees and extrapolated or interpolated to other ten angles covering uniformly the laboratory angular domain of 0 degrees to 180 degrees . The experimental set-up and procedures for data reduction including corrections and normalization are presented and discussed. Based on the measured double-differential cross sections, energy-differential and total cross sections are reported as well. Experimental cross sections are compared with similar available data from neutron- and proton-induced reactions. Theoretical calculations based on semiclassical exciton model and Hauser-Feshbach statistical theory (GNASH code) and intranuclear cascade model for nucleon-induced interactions (INCL3 code) were done and compared to the experimental results., Anglais

Double-differential cross sections for the production of protons, deuterons, tritons, and alpha particles from a silicon target were determined using fast incident neutrons. The inclusive charged particle emission spectra were measured at six laboratory angles, 20, 40, 60, 70, 110, and 140 deg, over the neutron energy range of 25 to 65 MeV. Representative results are shown for the cross-section differentials in energy and angle as well as for angle-integrated cross sections. The spectra are compared to existing data and with predictions from nuclear model calculations. Since the data for 62.7-MeV incident neutrons are the most complete, we emphasized these results; from the experimental energy-differential cross sections, the total charged particle production cross sections are determined as well as the partial and total kerma coefficients for silicon. Moreover, a comparison is done with our data on aluminum, for which exists a consistent set of measured cross sections in the same neutron energy region., Anglais

This paper presents the experimental set-up and data reduction procedures regarding the measurement of double-differential cross sections for light charged particle production in fast neutron induced reactions (n,px), (n,dx), (n,tx) and (n, alpha x) on bismuth in the incident neutron energy range 25-65 MeV and at laboratory angles from 20 degrees to 160 degrees . Preliminary double-differential and energy-differential cross sections for hydrogen isotopes are presented., Anglais

Experimental double-differential cross sections (d(2)sigma /d Omega dE) for fast neutron-induced proton, deuteron, triton, and alpha-particle production on aluminum are reported, at several incident neutron energies between 25 and 65 MeV, for outgoing particle energies above the experimental energy thresholds. Angular distributions were measured at laboratory angles between 20 degrees and 160 degrees. Reliable extrapolated spectra are derived for very forward (2.5 degrees and 10 degrees) and very backward angles (170 degrees and 177.5 degrees). Based on these experimental data, energy-differential (d sigma /dE), angle-differential (d sigma /d Omega), and total production cross sections (sigma (T)) are reported for each outgoing particle. (C) 2001 Academic Press.

The experimental setup of Louvain-1a-Neuve (UCL-Belgium) used to perform light-charged particle production experiment in fast neutron-induced reactions is presented. A short description of the neutron modular detector DEMON is also given. DEMON is a detector array for neutrons emitted in heavy ion induced reactions at low to intermediate energies.

Neutrons produced close to the Ge detectors of SPI can induce nuclear reactions, leading to the delayed emission of gamma -rays contributing to the background in the gamma -ray lines of astrophysical interest. The cross sections for such neutron-induced reactions were measured at Louvain-la-Neuve. This contribution report on last experiments dealing with the 122-136 keV gamma -rays from /sup 57/Co and the 1173-1332 keV gamma -rays from /sup 60/Fe., Anglais

Nuclear reactions induced by neutrons lead to the delayed emission of γ rays contributing to the instrumental background in γ-ray astrophysics missions in space. The cross sections for the reactions 27Al(n,2p)26Na, 27Al(n,α)24Na, and 56Fe(n,p)56Mn were measured up to a neutron energy of 50 or 65 MeV. A simple model was developed that allows one to extrapolate cross sections to higher energies. The magnitude of the instrumental background lines induced in the detectors of ESA's future INTEGRAL mission is deduced from our measurements., SCOPUS: ar.j, info:eu-repo/semantics/published

For nine incident neutron energies in the range 25 to 65 MeV, the double-differential cross sections (energy spectra) for the (n, px), (n, dx), (n, tx) and (n, alpha x) reactions on aluminium have been measured at lab angles between 20 degrees and 160 degrees in steps of 10 degrees. The partial and total kerma coefficients have been determined from the experimental energy-differential cross sections. The resulting partial kerma coefficients for the incident neutron energy range of 25-65 MeV are extrapolated to the threshold energy of each registered reaction product type. Only illustrative results of the experimental double-differential, energy-differential and total cross sections are presented. The deduced partial and total kerma coefficients of the present work are compared with results of previous integral measurements and theoretical predictions.

The double-differential cross sections for proton, deuteron, triton and alpha particle production in fast neutron induced reactions on carbon have been measured at several neutron energies from 25 to 75 MeV in the angular range from 20 degrees to 160 degrees. Experimental energy-differential, angle-differential and total cross sections are deduced, and consequently the partial and total kerma coefficients. The obtained experimental partial kerma coefficients are extrapolated down to the threshold energy of each measured reaction channel. Results on the experimental double differential, energy-differential and total cross sections are briefly presented. The deduced partial and total kerma coefficients of the present work are compared with previous measurements and theoretical predictions.

The present work summarizes our results already published on cross sections and partial kerma coefficients for hydrogen, carbon, and oxygen and then applies them for determining experimental partial and total kerma coefficients of composite biologically important materials. Double-differential cross sections for light-charged particle production (proton, deuteron, triton, and alpha particle) induced by fast neutrons on hydrogen, carbon, and oxygen have been experimentally measured at several incident energies from 25 to 75 MeV. The measurements covered the laboratory angular range 20 degrees to 160 degrees and were extended to very forward and very backward angles by using a reliable extrapolation procedure. Energy-differential, angle-differential, and total production cross sections were derived from the measured data. The experimental methods and data reduction procedures are briefly presented here. The experimental cross sections were compared to existing data in the literature for nucleon-induced reactions and against prediction of nuclear models. Partial and total elemental kerma coefficients were deduced on the basis of the measured cross sections. Procedures for extrapolating the partial kerma coefficients down to the reaction threshold energies for each of the measured ejectile species have been applied to carbon and oxygen. A simple-to-use analytical formula to describe the experimental hydrogen kerma coefficients was proposed which provides the recoil kerma coefficients in the incident neutron energy range 0.3 to 100 MeV. The present article reports for the first time experimental partial kerma coefficients for composite materials of biological interest. Resulting total kerma coefficients are compared to theoretical predictions and to other experimental data.

Experimental double-differential cross sections (d(2)sigma/d Omega dE) for fast neutron-induced production of proton, deuteron, triton, and alpha particle in carbon are reported at several incident neutron energies between 25 and 75 MeV. Angular distributions were measured in the laboratory angular range of 20 degrees to 160 degrees. Reliable extrapolated spectra are obtained at very forward (2.5 degrees and 10 degrees) and very backward (170 degrees and 177.5 degrees) angles. Based on these experimental data, energy differential (d sigma/dE), angle differential (d sigma/d Omega), and total cross sections (sigma(T)) are reported for each detected particle. (C) 2000 Academic Press.

Double-differential cross sections for proton and deuteron emission in fast neutron-induced reactions on carbon are reported at several incident neutron energies between 20 and 75 MeV. Angular distributions were measured at 15 laboratory angles between 20 degrees and 160 degrees. Procedures for data taking and data reduction are shortly presented. Deduced energy-differential, angle-differential and total cross sections are also reported. Experimental cross sections are compared with existing experimental data and with theoretical model calculations. (C) 2000 Elsevier Science B.V. All rights reserved.

The Pb-208(n,p)(208)T1 reaction cross section has been measured between 30 and 70 MeV neutron energy by the activation method. The results are compared with the predictions of a schematic model which includes contributions from direct reactions and compound nucleus formation.

Double-differential cross sections for fast neutron-induced triton and alpha-particle production on carbon are reported at six incident neutron energies between 40 and 75 MeV. Angular distributions were measured at laboratory angles between 20 degrees and 160 degrees. Energy-differential, angle-differential and total cross sections are also reported. Experimental cross sections are compared to existing experimental data and to theoretical model calculations. (C) 2000 Elsevier Science B.V. All rights reserved.

The 208Pb(n,p)208Tl reaction cross section has been measured between 30 and 70 MeV neutron energy by the activation method. The results are compared with the predictions of a schematic model which includes contributions from direct reactions and compound nucleus formation., SCOPUS: ar.j, info:eu-repo/semantics/published

The [Formula Presented] reaction cross section has been measured between 30 and 70 MeV neutron energy by the activation method. The results are compared with the predictions of a schematic model which includes contributions from direct reactions and compound nucleus formation. © 2000 The American Physical Society., SCOPUS: ar.j, info:eu-repo/semantics/published

Nuclear reactions induced by neutrons lead to the delayed emission of [Formula Presented] rays contributing to the instrumental background in [Formula Presented]-ray astrophysics missions in space. The cross sections for the reactions [Formula Presented] and [Formula Presented] were measured up to a neutron energy of 50 or 65 MeV. A simple model was developed that allows one to extrapolate cross sections to higher energies. The magnitude of the instrumental background lines induced in the detectors of ESA’s future INTEGRAL mission is deduced from our measurements. © 2000 The American Physical Society., SCOPUS: ar.j, info:eu-repo/semantics/published

Neutrons produced close to the Ge detectors of SPI can induce nuclear reactions, leading to the emission of β-delayed γ-rays, which is a possible cause of background in the γ-ray lines of astrophysical interest © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint., SCOPUS: ar.j, info:eu-repo/semantics/published

La dissertations présente les mesures expérimentales de sections efficaces doublement différentielles de production de particules légères (protons, deutons, tritons et alphas) induites par des neutrons rapides sur l'oxygène et l'aluminium, à neuf énergies de neutrons incidents. Les distributions angulaires couvrent 15 angles allant de 20° à 160° par pas de 10°. Pour les protons et deutons, les distributions angulaires sont complètes à toutes les énergies de neutrons. Dans le cas des tritons et alphas, du à une pauvre statistique, suels des spectres en énergie aux angles de l'hémisphère avant (entre 20° et 80°) ont pu être extraits, pour des énergies de neutrons à 62.7 MeV. Les mesures ont été prises au cyclotron de Louvain-la-Neuve (CYCLONE) où les neutrons sont produits en envoyant un faisceau de protons de 65 MeV sur une cible de lithium naturel. Le spectre de neutrons est composé d'un pic monocinétique à haute énergie (62.7 MeV) suivi d'une longue queue de neutrons d'énergie plus basse. Les données sur l'oxygène et l'aluminium ont été obtenues en plaçant successibement des cibles de Al2O3 et de Al dans la chambre à réaction. Les données sur oxygène sont obtenues par soustraction des spectres mesurés avec les deux cibles. Les distributions angulaires des spectres d'émission sont extrapolées vers les angles extrêmes (2.5°, 10°, 170° et 177.5°) à l'aide d'une formule simple. Celle-ci est également utilisées pour interpoler les données dans le cas où il y a des angles manquants et pour exptrapoler les distributions angulaires limitées à l'hémisphères avant. Obtenant ainsi un bon recouvrement angulaire, des sections efficaces différentielles en énergie do/dE pour les quatres types de particules sont déduites. De plus, après extrapolation en dessous des seuils de détections, des sections efficaces totales de production sont déterminées. A partir des sections efficaces microscopiques, les facteurs kerma partiels (protons, deutons, tritons et alphas) pour l'oxygène et l', (PHYS 3)--UCL, 1999

Experimental double-differential cross sections (d(2)sigma/d Omega dE) for fast neutron-induced proton, deuteron, triton, and alpha-particle production on oxygen are reported at several incident neutron energies between 25 and 65 MeV for outgoing particle energies above the experimental energy detection thresholds. Angular distributions were measured at laboratory angles between 20 degrees and 160 degrees. Reliable extrapolated spectra are obtained at very forward (2.5 degrees and 10 degrees) and at very backward (170 degrees and 177.5 degrees) angles. Based on these experimental data, energy-differential (d sigma/dE), angle-differential (d sigma/d Omega), and total cross sections (TT) are reported for each detected particle. (C) 1999 Academic Press.

Quasi-monoenergetic neutron beams in the energy range from about 25 to 70 MeV have been produced and accurately characterised at the accelerator facility of the Universite Catholique de Louvain (UCL), Belgium. The neutron fluence was determined with a proton recoil telescope and a liquid scintillation detector (NE213). The spectral fluence was measured employing the time-of-flight method with the NE213 detector and a U-238 fission ionisation chamber. The results obtained with the different methods are in agreement within the respective uncertainties. (C) 1999 Elsevier Science B.V. All rights reserved.

The reactions 9Be(n,3n)7Be and 56Fe(n,p)56Mn were measured between 28 and 68 MeV and at 28 MeV, respectively. These reactions lead to the emission of γ-rays (478, 847, 1811 keV) that may be disturbing in γ-ray astrophysics missions. Consequences regarding the induced background in detectors are drawn. © 1998 Elsevier Science B.V. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

The double-differential cross sections (energy spectra) for the (n, px), (n, dx), (n, tx) and (n, rx) reactions on oxygen have been measured for nine incident neutron energies in the range 25 to 65 MeV at lab angles between 20 degrees and 160 degrees in steps of 10 degrees. From these measurements, the energy differential cross sections have been determined and consequently the partial and total kerma factors. Based on the obtained experimental partial kerma factors in the incident neutron energy range 25-65 MeV, a procedure is proposed for the extrapolation of these values to the reaction threshold energy of each measured reaction channel. Results of the experimental double-differential, energy differential and total cross sections are presented. The deduced partial and total kerma factors of the present work are compared with results of previous measurements and theoretical predictions.

Double-differential cross sections for fast neutron induced triton and alpha-particle production on oxygen, are reported at seven incident neutron energies between 30 and 65 MeV. Angular distributions were measured at laboratory angles between 20 degrees and 160 degrees. Energy-differential, angle-differential and total cross sections are reported. Experimental cross sections are compared with existing experimental data and with theoretical model calculations.

Double-differential cross sections (energy spectral) for proton and deuteron emission in fast neutron induced reactions on oxygen are reported for nine incident neutron energies between 25 and 65 MeV. Angular distributions were measured at 15 laboratory? angles between 20 degrees and 160 degrees. Procedures for data laking and data reduction are presented. Deduced energy-differential, angle-differential and total cross sections are also reported. Experimental cross sections are compared with existing data and with theoretical model calculations.

The reactions Be-9(n,3n)Be-7 and Fe-56(n,p)Mn-56 were measured between 28 and 68 MeV and at 28 MeV, respectively. These reactions lead to the emission of gamma-rays (478, 847, 1811 keV) that may be disturbing in gamma-ray astrophysics missions. Consequences regarding the induced background in detectors are drawn. (C) 1998 Elsevier Science B.V. All rights reserved.