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Featured researches published by A.P. Jesus.


Geodinamica Acta | 2007

The Beja Layered Gabbroic Sequence (Ossa-Morena Zone, Southern Portugal): geochronology and geodynamic implications

A.P. Jesus; José Munhá; António Mateus; Colombo C. G. Tassinari; Allen P. Nutman

The Beja Igneous Complex (BIC) is a major geological feature in SW Iberian Variscides, consisting of three main units developed during different stages of the oblique collision between the Ossa Morena Zone (OMZ) upper plate and South Portuguese Zone (SPZ) lower plate, namely: (1) ca. 355 Ma to ca. 345 Ma Layered Gabbroic Sequence formed in early stages of collision magmatism; (2) the ca. 335-330 Ma to ca. 320 Ma Cuba-Alvito (gabbro-diorite) Complex formed throughout the late-collision magmatic event; and (3) the Baleizão Porphyry Complex corresponding to the period of post-collision magmatism, ca. 300 Ma. The new SHRIMP U-Pb age of 342±9 Ma reported here for amphibole-bearing pegmatite dykes cutting the layered gabbros is interpreted as dating the development of late fluid-rich melts in the Layered Gabbroic Sequence, synchronous with Fe-Cu-Co sulphide deposition. The close agreement between this data and available amphibole 40Ar/39Ar ages of BIC, Beja-Acebuches Ophiolite and other geological units of the OMZ southern border, may be taken as evidence for a moderate to rapid regional crustal uplift episode at ca. 340±5 Ma; this data, coupled with structural constraints, also allow to estimate the age for the transition between the D2a – D2b deformation phases of Variscan continental collision. A complex wedge system within the SW Iberian Variscides developed during this collision, involving the OMZ upper plate to the north and the SPZ passive margin in the lower plate. The Évora-Beja-Aracena Domain, located in the upper plate above the N-dipping subduction zone, is re-interpreted as a retro-wedge domain that was kinematically coupled to the SPZ pro-wedge and subduction system. Retro-wedge growth is linked to upper plate uplift (early collision) and a late-orogenic wedge thickening. The early stages of magmatism in the retro-wedge are related to asthenospheric mantle upwelling induced by the slab break-off. Regional LP-HT metamorphism and subsequent magmatic events in the retro-wedge domain were caused by long term high heat flow sustained by (1) mafic magma underplating, (2) stacking of high-heat producing upper-crustal lithologies, and reinforced (3) by (moderate to) rapid crustal uplifting. Mass advection and orogenic architecture were strongly affected by asymmetric removal towards the lower-part foreland basin and by transient mechanical properties of the wedge system associated with the anomalous thermal regime.


Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 1996

Matrix effects correction for quantitative TTPIXE analysis

M.A. Reis; L.C. Alves; A.P. Jesus

Abstract The use of thick targets in PIXE analysis has many advantages, namely the smaller probability of significative contamination, easy target handling and preparation. Also in some applications as archaeometry, materials sciences and many others, the use of thick targets is imperative. A correct calculation of the thick target yield is then needed in order to obtain good results. In this work, corrections for the enhancement effects due to secondary X-ray fluorescence in metal alloys and due to radiation damage in biological samples are proposed. Numerical integration problems in critical matrix absorption situations are also presented.


Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 1996

Experimental X-ray peak-shape determination for a Si(Li) detector

L.C. Alves; A.P. Jesus; Maria A.M. Reis

The response function of a Si(Li) detector to monochromatic radiation was determined in the energy region between 1.7 and 10 keV. A wavelength dispersive spectrometer with a plane Bragg crystal was used to select the X-ray lines to be analysed. The chosen targets were irradiated with 1.8 MeV protons. Some modifications were introduced to the known HYPERMET function in order to describe the peak shapes observed. An energy dependent function was then determined involving the parameters used in the detector response function. The energy dispersive analysis of the Mn K radiation resulting from the decay of a55Fe radioactive source, revealed additional radiative contributions to the peak shape observed, attributed to the Auger radiative effect and to the Mn Kβ5 line.


Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 1998

Enhanced X-ray yields from insulating samples

A.P. Jesus; M.A. Reis; L.C. Alves

Abstract Some insulating samples under proton bombardment produce a very large bremsstrahlung background and enhanced X-ray lines. X-ray energy spectra of several insulating samples (fluorides of metals with valence 4, 3, 2 and 1, a fluoride glass and three fluoride free samples) are presented for proton energies from 0.175 to 2.00 MeV. Also, multiscaling spectra have been collected in order to relate the X-ray yield enhancement with the sample charging up process. It may be concluded that the enhancement effect is obtained during the charged state of the samples and not during the discharge and that structural properties of the samples rather than their insulating properties play an important role in producing and keeping that charged state. Considerations of ionization cross section values suggest high energy electrons as the main ionizing agent. It is also shown that some samples can hold the charged state, with corresponding high X-ray yields, for long periods, suggesting their use as X-ray sources.


Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 2016

Cross sections for proton induced high energy γ-ray emission (PIGE) in reaction 19F(p,αγ)16O at incident proton energies between 1.5 and 4 MeV

P. Cabanelas; J. Cruz; M. Fonseca; A. Henriques; F. Lourenço; H. Luis; Joana Machado; J. Pires Ribeiro; A.M. Sánchez-Benítez; P. Teubig; P. Velho; M. Zarza-Moreno; D. Galaviz; A.P. Jesus

Abstract We have studied the high energy gamma-rays produced in the reaction 19 F(p, α γ ) 16 O for incident proton energies from 1.5 to 4.0xa0MeV over NaF/Ag and CaF2/Ag thin targets in two different sets of data. Gamma-rays were detected with a High Purity Ge detector with an angle of 130° with respect to the beam axis. The cross-sections for the high energy gamma-rays of 6.129, 6.915 and 7.115xa0MeV have been measured for the whole group between 5 and 7.2xa0MeV with accuracy better than 10%. A new energy range was covered and more points are included in the cross-sections data base expanding the existing set of data. Results are in agreement with previous measurements in similar conditions.


Journal of Physics: Conference Series | 2012

Electron screening effects in nuclear reactions: still an unsolved problem

J. Cruz; H. Luis; M. Fonseca; A.P. Jesus

Electron screening for nuclear reactions in metals plays an unexpected and important role in enhancing reaction cross sections in the ultra-low energy region. Even though there are still some discrepancies between experimental data from different authors, the enhanced screening effect in metallic environments is well established, and attributed to the quasi-free valence electrons in the metals. However, there is still no solid theory which can describe quantitatively the observed enhancements. In the present work, experimental and theoretical results obtained so far will be overviewed, and a proposal to improve our knowledge on this subject.


Journal of Physics: Conference Series | 2016

Study of nuclear reactions producing 36Cl by micro-AMS

H. Luís; A.P. Jesus; M. Fonseca; J. Cruz; D. Galaviz; N Franco; E. Alves

36Cl is one of several short to medium lived isotopes (as compared to the earth age) whose abundances at the earlier solar system may help to clarify its formation process. There are two generally accepted possible models for the production of this radionuclide: it originated from the ejecta of a nearby supernova (where 36Cl was most probably produced in the s-process by neutron irradiation of 35Cl) and/or it was produced by in-situ irradiation of nebular dust by energetic particles (mostly, p, a, 3He -X-wind irradiation model).The objective of the present work is to measure the cross section of the 37Cl(p,d)36Cl and 35Cl(d,p)36Cl nuclear reactions, by measuring the 36Cl content of AgCl samples (previously bombarded with high energy protons and deuterons) with AMS, taking advantage of the very low detection limits of this technique for chlorine measurements.For that, the micro-AMS system of the LF1/ITN laboratory had to be optimized for chlorine measurements, as to our knowledge this type of measurements had never been performed in such a system (AMS with micro-beam).Here are presented the first results of these developments, namely the tests in terms of precision and reproducibility that were done by comparing AgCl blanks irradiated at the Portuguese National Reactor with standards produced by the dilution of the NIST SRM 4943 standard material.


Archive | 2005

Intercummulus massive Ni-Cu-Co and PGE-bearing sulphides in pyroxenite: a new mineralization type in the layered gabbroic sequence of the Beja Igneous Complex (Portugal)

A.P. Jesus; António Mateus; José Munhá; Álvaro Pinto

Coarse-grained pyroxenite cumulates occurring within an olivine leucogabbro/pyroxenite gabbro rhythmic suite host a new sulphide mineralization type in the Beja Layered Gabbroic Sequence, Portugal. The sulphides formed in an intercummulus phase as a result of the coalescence of disseminated blebs of pyrrhotite with abundant pentlandite and chalcopyrite exsolutions, gradually disrupting the silicate matrix. Intra- and inter-granular veinlets are sealed by Ni-rich minerals of the linnaeite group, with decreasing Co content from earlier to later generations. The deposition of Ni (± Co)-rich pyrite represents the late mineral infill in the linnaeite veins. Pyrite veinlets and subhedral grains in the pyrrhotite groundmass display gradually lower Ni contents with time. Chalcopyrite is the latest sulphide phase, sealing micro-fractures and replacing pre-existing sulphides. EPMA data revealed concentrations up to 1500 ppm of Pt, Pd, Au, Ag Cd and Bi in pentlandite, chalcopyrite and in minerals of the linnaeite group.


Gondwana Research | 2010

Variscan ophiolite belts in the Ossa-Morena Zone (Southwest Iberia): Geological characterization and geodynamic significance

António Ribeiro; José Munhá; Paulo E. Fonseca; Alexandre Araújo; Jorge Pedro; António Mateus; Colombo C. G. Tassinari; Gil Machado; A.P. Jesus


Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 2004

Measurement of the inelastic scattering of protons by 23Na in the energy range 1.25–2.40 MeV

R. Mateus; A.P. Jesus; J. Cruz; J.P. Ribeiro

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J. Cruz

Universidade Nova de Lisboa

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L.C. Alves

Instituto Superior Técnico

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H. Luis

University of Lisbon

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C. Santos

Universidade Nova de Lisboa

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H. Silva

Universidade Nova de Lisboa

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