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9 results on '"capture cross-sections"'

1. Isotope Dichotomy from Solar Protoplanetary Disk Processing of 150Nd-rich Stellar Ejecta

Author

Saji, Nikitha Susan, Schiller, Martin, Holst, Jesper Christian, Bizzarro, Martin, Saji, Nikitha Susan, Schiller, Martin, Holst, Jesper Christian, and Bizzarro, Martin

Abstract

We use high-precision neodymium isotope data for sequentially acid-leached components of the primitive carbonaceous chondrite Tagish Lake to identify a non-classical Nd-150-rich presolar carrier phase that has not been identified as of yet in meteorites. The distinct isotopic signature of this carrier can be attributed to the intermediate neutron capture process (i-process) occurring in asymptotic giant branch (AGB), super-AGB, or post-AGB stars or, alternatively, the slow capture process (s-process) occurring in rotating massive stars. The Nd-150-rich carrier appears to be heterogeneously distributed in the solar protoplanetary disk resulting in systematic isotope variations between carbonaceous and non-carbonaceous solar system materials. Carbonaceous chondrites that accreted in the outer disk are depleted in this carrier relative to non-carbonaceous materials that accreted in the terrestrial planet-forming region. Calcium-aluminum-rich inclusions that represent the earliest formed disk solids record the largest depletion of this carrier. This distribution pattern is contrary to that seen for the carriers of other neutron-rich isotope anomalies (Ca-48, Cr-54, Mo-95,Mo-97, etc.) that have defined carbonaceous/non-carbonaceous isotope dichotomy so far. Irrespective of the exact astrophysical origin of these carriers, divergent distribution of presolar dust as a function of physicochemical processing in the solar protoplanetary disk best explains the solar system isotope dichotomy as opposed to changes in the composition of the infall.

Published
2021

2. Isotope Dichotomy from Solar Protoplanetary Disk Processing of 150Nd-rich Stellar Ejecta

Author

Nikitha Susan Saji, Martin Schiller, J. C. Holst, and Martin Bizzarro

Subjects
ANOMALIES, CAPTURE CROSS-SECTIONS, Protoplanetary disk, 01 natural sciences, Astrobiology, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, HETEROGENEITY, Ejecta, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, Isotope, 010308 nuclear & particles physics, ORIGIN, LOW-METALLICITY, Astronomy and Astrophysics, Meteorite, 13. Climate action, Space and Planetary Science, Physics::Space Physics, Circumstellar dust, NEUTRON-CAPTURE, Astrophysics::Earth and Planetary Astrophysics, ND, S-PROCESS, MASSIVE STARS, BUILDING-BLOCKS
Abstract

We use high-precision neodymium isotope data for sequentially acid-leached components of the primitive carbonaceous chondrite Tagish Lake to identify a non-classical 150Nd-rich presolar carrier phase that has not been identified as of yet in meteorites. The distinct isotopic signature of this carrier can be attributed to the intermediate neutron capture process (i-process) occurring in asymptotic giant branch (AGB), super-AGB, or post-AGB stars or, alternatively, the slow capture process (s-process) occurring in rotating massive stars. The 150Nd-rich carrier appears to be heterogeneously distributed in the solar protoplanetary disk resulting in systematic isotope variations between carbonaceous and non-carbonaceous solar system materials. Carbonaceous chondrites that accreted in the outer disk are depleted in this carrier relative to non-carbonaceous materials that accreted in the terrestrial planet-forming region. Calcium-aluminum-rich inclusions that represent the earliest formed disk solids record the largest depletion of this carrier. This distribution pattern is contrary to that seen for the carriers of other neutron-rich isotope anomalies (48Ca, 54Cr, 95,97Mo, etc.) that have defined carbonaceous/non-carbonaceous isotope dichotomy so far. Irrespective of the exact astrophysical origin of these carriers, divergent distribution of presolar dust as a function of physicochemical processing in the solar protoplanetary disk best explains the solar system isotope dichotomy as opposed to changes in the composition of the infall.

Published
2021

3. DYNAMICS OF FREE CARRIERS - NEUTRAL IMPURITY RELATED OPTICAL TRANSITIONS IN BE AND Si δ-DOPED GaAs/AIAs MULTIPLE QUANTUM WELLS: FRACTIONAL-DIMENSIONAL SPACE APPROACH.

Author

Kundrotas, J., Čerškus, A., Valušis, G., Linfield, E. H., Johannessen, E., and Johannessen, A.

Subjects
*GALLIUM arsenide, *SILICON, *DOPED semiconductors, *OPTICAL properties of aluminum arsenide, *QUANTUM wells, *PHASE transitions, *METAL inclusions
Abstract

The dynamics of impurity-related optical transitions in 20 nm wide silicon and beryllium δ-doped GaAs/AlAs multiple quantum wells with various doping levels has been investigated at near liquid helium temperatures. The radiative lifetimes of the free electron-neutral acceptor and the free hole-neutral donor have been identified. The capture cross-sections of the free electrons by neutral Be acceptors were experimentally determined to σe-Be = 4 × 10-10 cm, whereas this corresponded to σh-Si = 2.2 × 10-8 cm for the free holes by neutral Si donors. The experimentally determined cross-section ratio of σh-Si/σe-Be = 55 is close to the estimated 2D value of σh-D /σe-A = 64 and remains lower compared to the calculated value for the 3D case of σh-D/σe-A = 121. [ABSTRACT FROM AUTHOR]

Published
2014

4. 232Th, 233Pa, and 234U capture cross-section measurements in moderated neutron flux

Author

Bringer, O., Isnard, H., AlMahamid, I., Chartier, F., and Letourneau, A.

Subjects
*NEUTRONS, *FUSED salts, *MASS spectrometry, *IRRADIATION
Abstract

Abstract: The Th–U cycle was studied through the evolution of a 100μg 232Th sample irradiated in a moderated neutron flux of 8.01014 n/cm2/s, intensity close to that of a thermal molten salt reactor. After 43 days of irradiation and 6 months of cooling, a precise mass spectrometric analysis, using both TIMS and MC-ICP-MS techniques, was performed, according to a rigorous methodology. The measured thorium and uranium isotopic ratios in the final irradiated sample were then compared with integral simulations based on evaluated data; an overall good agreement was seen. Four important thermal neutron-capture cross-sections were also extracted from the measurements, 232Th (7.34±0.21b), 233Pa (38.34±1.78b), 234U (106.12±3.34b), and 235U (98.15±11.24b). Our 232Th and 235U results confirmed existing values whereas the cross-sections of 233Pa and 234U (both key parameters) have been redefined. [Copyright &y& Elsevier]

Published
2008
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6. (96)Zr(n,gamma) measurement at the n_TOF facility at CERN

Author

Tagliente, G., Milazzo, P. M., Fujii, K., Abbondanno, U., Aerts, G., Alvarez, H., Alvarez-Velarde, F., Andriamonje, S., Andrzejewski, J., Audouin, L., Badurek, G., Baumann, P., Becvar, F., Belloni, F., Berthoumieux, E., Calvino, F., Calviani, M., Cano-Ott, D., Capote, R., Carrapico, C., Cennini, P., Chepel, V., Chiaveri, E., Colonna, N., Cortes, G., Couture, A., Dahlfors, M., David, S., Dillmann, I., Domingo-Pardo, C., Dridi, W., Duran, I., Eleftheriadis, C., Embid-Segura, M., Ferrari, A., Ferreira-Marques, R., Furman, W., Goncalves, I., Gonzalez-Romero, E., Gramegna, F., Guerrero, C., Gunsing, F., Haas, B., Haight, R., Heil, M., Herrera-Martinez, A., Jericha, E., Kappeler, F., Kadi, Y., Karadimos, D., Karamanis, D., Kerveno, M., Kossionides, E., Krticka, M., Lamboudis, C., Leeb, H., Lindote, A., Lopes, I., Lukic, S., Marganiec, J., Marrone, S., Martinez, T., Massimi, C., Mastinu, P., Mengoni, A., Moreau, C., Mosconi, M., Neves, F., Oberhummer, H., O'Brien, S., Pancin, J., Papachristodoulou, C., Papadopoulos, C., Paradela, C., Patronis, N., Pavlik, A., Pavlopoulos, P., Perrot, L., Pigni, M. T., Plag, R., Plompen, A., Plukis, A., Poch, A., Praena, J., Pretel, C., Quesada, J., Reifarth, R., Rosetti, M., Rubbia, C., Rudolf, G., Rullhusen, P., Salgado, J., Santos, C., Sarchiapone, L., Savvidis, I., Stephan, C., Tain, J. L., Tassan-Got, L., Tavora, L., Terlizzi, R., Vannini, G., Vaz, P., Ventura, A., Villamarin, D., Vincente, M. C., Vlachoudis, V., Vlastou, R., Voss, F., Walter, S., Wiescher, M., Wisshak, K., and N TOF Collaboration

Subjects
silicon-carbide, elements, statistical-model, massive stars, nuclear-science, primitive meteorites, giant branch stars, capture cross-sections, s-process nucleosynthesis, neutron-capture
Abstract

The (n,gamma) cross section of (96)Zr has been investigated at the CERN n_TOF spallation neutron source. High-resolution time-of-flight measurements using an enriched ZrO(2) sample allowed us to analyze 15 resonances below 40 keV with improved accuracy. On average, the capture widths were found to be 25% smaller than reported in earlier experiments. If complemented with the contribution by direct radiative capture, the derived Maxwellian averaged cross sections are consistent with activation data at kT = 25 keV. The present results confirm the astrophysical implications for the s-process branching at (95)Zr. Physical Review C

Published
2011

7. The (92)Zr(n,gamma) reaction and its implications for stellar nucleosynthesis

Author

Tagliente, G., Milazzo, P. M., Fujii, K., Abbondanno, U., Aerts, G., Alvarez, H., Alvarez-Velarde, F., Andriamonje, S., Andrzejewski, J., Audouin, L., Badurek, G., Baumann, P., Becvar, F., Belloni, F., Berthoumieux, E., Bisterzo, S., Calvino, F., Calviani, M., Cano-Ott, D., Capote, R., Carrapico, C., Cennini, P., Chepel, V., Chiaveri, E., Colonna, N., Cortes, G., Couture, A., Cox, J., Dahlfors, M., David, S., Dillmann, I., Domingo-Pardo, C., Dridi, W., Duran, I., Eleftheriadis, C., Embid-Segura, M., Ferrari, A., Ferreira-Marques, R., Furman, W., Gallino, R., Goncalves, I., Gonzalez-Romero, E., Gramegna, F., Guerrero, C., Gunsing, F., Haas, B., Haight, R., Heil, M., Herrera-Martinez, A., Igashira, M., Jericha, E., Kappeler, F., Kadi, Y., Karadimos, D., Karamanis, D., Kerveno, M., Kossionides, E., Krticka, M., Lamboudis, C., Leeb, H., Lindote, A., Lopes, I., Lozano, M., Lukic, S., Marganiec, J., Marrone, S., Martinez, T., Massimi, C., Mastinu, P., Mengoni, A., Moreau, C., Mosconi, M., Neves, F., Oberhummer, H., O'Brien, S., Pancin, J., Papachristodoulou, C., Papadopoulos, C., Paradela, C., Patronis, N., Pavlik, A., Pavlopoulos, P., Perrot, L., Pigni, M. T., Plag, R., Plompen, A., Plukis, A., Poch, A., Praena, J., Pretel, C., Quesada, J., Rauscher, T., Reifarth, R., Rosetti, M., Rubbia, C., Rudolf, G., Rullhusen, P., Salgado, J., Santos, C., Sarchiapone, L., Savvidis, I., Stephan, C., Tain, J. L., Tassan-Got, L., Tavora, L., Terlizzi, R., Vannini, G., Vaz, P., Ventura, A., Villamarin, D., Vincente, M. C., Vlachoudis, V., Vlastou, R., Voss, F., Walter, S., Wendler, H., Wiescher, M., Wisshak, K., and N TOF Collaboration

Subjects
n-tof, elements, zr isotopes, facility, energy range, cern, capture cross-sections, giant branch stars, neutron-capture, s-process
Abstract

Because the relatively small neutron capture cross sections of the zirconium isotopes are difficult to measure, the results of previous measurements are often not adequate for a number of problems in astrophysics and nuclear technology. Therefore, the (92)Zr(n,gamma) cross section has been remeasured at the CERN n_TOF facility, providing a set of improved parameters for 44 resonances in the neutron energy range up to 40 keV. With this information the cross-section uncertainties in the keV region could be reduced to 5% as required for s-process nucleosynthesis studies and technological applications. Physical Review C

Published
2010

8. Experimental study of the 91Zr(n gamma) reaction up to 26 keV

Author

Tagliente, G, Milazzo, P M, Fujii, K, Aerts, G, Abbondanno, U, Alvarez, H, Alvarez-Velarde, F, Andriamonje, Samuel A, Andrzejewski, J, Assimakopoulos, Panayiotis, Audouin, L, Badurek, G, Baumann, P, Becvár, F, Belloni, F, Berthoumieux, E, Calviño, F, Calviani, M, Cano-Ott, D, Capote, R, Carrapiço, C, Cennini, P, Chepel, V, Colonna, N, Cortés, G, Couture, A, Cox, J, Dahlfors, M, David, S, Dillmann, I, Domingo-Pardo, C, Dridi, W, Durán, I, Eleftheriadis, C, Embid-Segura, M, Ferrant, L, Ferrari, A, Ferreira-Marques, R, Furman, W, Gonçalves, I, Gonzalez-Romero, E, Gramegna, F, Guerrero, C, Gunsing, F, Haas, B, Haight, R, Heil, M, Herrera-Martínez, A, Igashira, M, Jericha, E, Kappeler, F, Kadi, Y, Karadimos, D, Karamanis, D, Kerveno, M, Köhler, P, Kossionides, E, Krticka, M, Lamboudis, C, Leeb, H, Lindote, A, Lopes, I, Lozano, M, Lukic, S, Marganiec, J, Marrone, S, Martínez, T, Massimi, C, Mastinu, P, Mengoni, A, Moreau, C, Mosconi, M, Neves, F, Oberhummer, H, O'Brien, S, Pancin, J, Papachristodoulou, C, Papadopoulos, C, Paradela, C, Patronis, N, Pavlik, A, Pavlopoulos, P, Perrot, L, Pigni, M T, Plag, R, Plompen, A, Plukis, A, Poch, A, Praena-Rodriguez, J, Pretel, C, Quesada, J, Rauscher, T, Reifarth, R, Rubbia, C, Rudolf, G, Rullhusen, P, Salgado, J, Santos, C, Sarchiapone, L, Savvidis, I, Stéphan, C, Taín, J L, Tassan-Got, L, Tavora, L, Terlizzi, R, Vannini, G, Vaz, P, Ventura, A, Villamarín, D, Vincente, M C, Vlachoudis, V, Vlastou, R, Voss, F, Walter, S, Wiescher, M, Wisshak, K, Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée (DAPNIA), Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Département Recherches Subatomiques (DRS-IPHC), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Louis Pasteur - Strasbourg I-Centre National de la Recherche Scientifique (CNRS), Laboratori Nazionali di Legnaro (LNL), Istituto Nazionale di Fisica Nucleare (INFN), European Organization for Nuclear Research (CERN), Institut de Physique Nucléaire d'Orsay (IPNO), Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Centre d'Etudes Nucléaires de Bordeaux Gradignan (CENBG), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Istituto Nazionale di Fisica Nucleare, Sezione di Bologna (INFN, Sezione di Bologna), nTOF, Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11), Université Sciences et Technologies - Bordeaux 1-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), and National Institute for Nuclear Physics (INFN)

Subjects
statistical-model, Astrophysics::High Energy Astrophysical Phenomena, Nuclear Theory, cern, transmission, nucleosynthesis, capture cross-sections, [PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex], 25.40.Lw, 25.70.Ef, 27.60.+j, 97.10.Cv, n-tof, evolution, Nuclear Physics - Experiment, giant branch stars, Nuclear Experiment, neutron-capture, s-process
Abstract

The neutron capture cross sections of the Zr isotopes are relevant to studies in nuclear structure, nuclear astrophysics, and nuclear technology. The valence neutron of (91)Zr with respect to the neutron magic nucleus (90)Zr has interesting implications for the statistical analysis in the proximity of shell closures. In stellar nucleosynthesis, the Zr isotopes are important for the s-process reaction flow between the Fe seeds and the heavier isotopes. Because of its relatively small (n, gamma) cross sections, Zr represents also an interesting structural material for nuclear reactors. For the same reason, these cross sections are difficult to measure and reliable data are sparse. Therefore, the (n, gamma) cross sections of the Zr isotopes have been remeasured at the CERN n_TOF facility. Thanks to its high instantaneous flux, good energy resolution, and low background, this facility is particularly suited for the determination of small, resonance-dominated cross sections. In this work, results for the (91)Zr(n, gamma) (92)Zr reaction are reported in the neutron energy range from thermal to 26 keV. In this region, accurate data of 157 resonances could be obtained, 33 of these resonances are not present in the main databases and/or were observed for the first time. Physical Review C

Published
2008

9. Links between hydrogen bonding, residual stress, structural properties and metastability in hydrogenated nanostructured silicon thin films

Author

Vignoli, S., Butte, R., Meaudre, R., Meaudre, M., and Brenier, R.

Subjects
CHEMICAL-VAPOR-DEPOSITION, AMORPHOUS-SILICON, A-SI-H, POLYMORPHOUS SILICON, DENSITY-OF-STATES, CAPTURE CROSS-SECTIONS, MICROCRYSTALLINE SILICON, LIGHT-SOAKING, VIBRATIONAL-SPECTRA, INFRARED-SPECTROSCOPY
Abstract

We present a systematic study of the local hydrogen bonding in hydrogenated polymorphous silicon thin films (pm-Si:H), a heterogeneous material deposited on the edge of crystallinity, by means of Fourier transform infrared spectroscopy. A vibrational mode at similar to2030 cm(-1) is reported and attributed to hydrogen atoms bonded in hydrogen-rich regions present at the interface between ordered regions and the amorphous matrix. This assignment is found to be in good agreement with previous spectroscopic ellipsometry and Raman spectroscopy studies. Combined with stress measurements we draw a picture of the nanostructure of pm-Si:H films, namely a two-domain material exhibiting: (i) large fluctuations of H content, (ii) a high mass density and (iii) the coexistence of highly strained crystalline phases with a relaxed amorphous matrix. Unexplained optoelectronic properties and metastability phenomena can also be accounted for by this picture.

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