Wiggly Strings in Linearized Brans-Dicke Gravity

The metric around a wiggly cosmic string is calculated in the linear approximation of Brans-Dicke theory of gravitation. The equations of motion for relativistic and non-relativistic particles in this metric are obtained. Light propagation is also studied and it is shown that photon trajectories can be bounded.Comment: 10 pages, LaTeX, added reference

Reactions with light exotic nuclei

CNR*13 - Fourth International Workshop on Compound Nuclear Reactions and RelatedExperimental cross sections for the 6He+120Sn are analysed. Elastic scattering angular distributions and alpha particle production cross sections have been measured and are compared with the total reaction cross section

Understanding the mechanisms of nuclear collisions: A complete study of the 10 B + 120 Sn reaction

Background: Reactions involving exotic and stable weakly bound nuclei have been extensively studied in recent years. Although several models have been successfully used to explain particular reaction outcomes, the answers to many questions remain elusive. In previous works, we presented elastic, inelastic, and transfer angular distributions for the 10B + 120Sn system measured at ELab = 31.5, 33.0, 35.0, and 37.5 MeV. The data set was analyzed through coupled reaction channels calculations in the context of the double-folding São Paulo potential. Purpose: We investigate nuclear reaction mechanisms for systems involving weakly bound projectiles. Method: Angular distributions for several nuclear reaction processes were measured for the 10B + 120Sn system at ELab = 39.70 MeV. Results: The new data set involves angular distributions for elastic scattering, projectile and target inelastic excitations, one-neutron pickup transfer, one-proton stripping transfer, deuteron pickup transfer, and 3,4 He stripping transfer. We have also observed 10Be nuclei. The effect of the couplings to some nonelastic states on the angular distributions is discussed. Conclusion: The theoretical calculations within the coupled reaction channels formalism provide an overall good agreement with the corresponding inelastic, one-neutron stripping, one-proton pickup, one-deuteron pickup, and 3 He stripping transfer data. However, to improve the description of the elastic scattering angular distribution, the inclusion of additional channels in the coupling scheme might be necessary.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) 2018/09998-8, 2019/07767-1, 2019/05769-7 y 2017/05660-0;Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) 304056/2019-7, 302160/2018-3 y 306433/2017- 6Instituto Nacional de Ciência e Tecnologia-Física Nuclear e Aplicações (INCT-FNA) 464898/2014-5Ministerio de Ciencia, Innovación y Universidades de España. PGC2018-096994-B-C21Ministerio de Economía de España y Competitividad y fondos FEDER. FIS2017-88410-

Investigation of the fusion process for B 10 + Au 197 at near-barrier energies

In a previous work, we presented data for the B10+Au197 system, corresponding to quasielastic and elastic scattering, Au197 inelastic excitation, and one neutron pickup transfer, measuring the angular distribution of scattered beam-like ejectiles at several energies around the Coulomb barrier. In this paper, we present data for the fusion process of the same system, at several energies around the Coulomb barrier, as well as new data for one neutron pickup and stripping transfer. In this case, we detected offline γ rays stemming from the β-delayed decay chain of fusion-evaporation residues and heavy transfer products. As in our previous work, we analyzed this data set with coupled reaction channels calculations using the São Paulo potential. We show that the coupling to the one neutron transfer channel is quite important to describe the fusion data at the sub-barrier energy region. We also provide a comparison of the experimental fusion cross sections obtained for B10+Au197 with data for several other systems involving the same target nucleus.Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, Argentina) PIP00786COFondo para la Investigacin Cientfica y Tecnolgica (FONCYT, Argentina) PICT-2017-4088Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP, Brazil) 2018/09998-8, 2019/07767-1, 2019/05769-7Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil) 302160/2018-3, 304056/2019-7Ministerio de Ciencia, Innovación y Universidades PGC2018-096994-B-C2

Determination of total I and 129

Total iodine and129-iodine in rivers and lakes of Argentina were measured by means of inductively coupled plasma mass spectrometry and accelerator mass spectrometry respectively. The obtained isotopic ratios, higher than the natural level, are explained as the delayed signal from nuclear weapon atmospheric tests. Besides, deposition fluences in catchment areas of the lakes are analyzed. Their latitudinal dependence, similar to the dependence of annual precipitation rates, favours wet deposition as the main 129I fallout mechanism for this region

Measurements of the 25Mg(p, gamma )

La reacción 25Mg(p,γ) es el principal mecanismo de producción estelar del radioisótopo 26Al. Dada la vida media del 26Al(τ~ 10 6 a), este radioisótopo puede escapar de la estrella quelo origina y decaer en el medio interestelar. La detección de la radiación gamma generada eneste decaimiento permite rastrear los sitios de producción de 26 Al en la Vía Láctea y ajustarasí los modelos de nucleosíntesis. Para esto último es necesario, además, precisar la tasa deproducción de la reacción resonante 25Mg(p,γ)26 Al en el rango de energías estelares. Previo a este estudio, las intensidades de las resonancias de esta reacción se determinaronmediante la detección en línea de rayos gamma de desexcitación del núcleo compuesto 26Al. Sin embargo, a las energías estelares, muy por debajo de la barrera coulombiana, la reaccióntiene una producción en extremo baja y su medición se dificulta por causa del fondo gammaambiental y el fondo producido por reacciones en elementos contaminantes. Para eludir estos inconvenientes, en este trabajo se desarrolló un método de mediciónalternativo, basado en la alta sensibilidad de la espectrometría de masas con aceleradores (AMS). En este método, se bombardean blancos de MgO con un gran número de protones (del orden de 10 19)a las energías de resonancia. A continuación, estos blancos son tratadosquímicamente, agregando y homogeneizando una cantidad bien determinada del isótopoestable 27 Al y eliminando el Mg que lo componía originalmente. Las muestras así generadascontienen el 26Al producido en la reacción p + 25Mg y la cantidad de los mismos se determinamidiendo la concentración 26Al/27Al mediante la técnica AMS. La pequeña cantidad de 26Al presente en las muestras (del orden de 10 6 - 10 7 átomos) hizonecesario optimizar la eficiencia de detección. A estos efectos, las mediciones de concentraciónde las muestras se realizaron extrayendo es estas el ion molecular 26AlOˉ de la fuente de iones. Dado que el ion molecular es hasta 25 veces más prolífico que el ion atómico Alˉ utilizadousualmente, su empleo permitió incrementar la eficiencia de detección hasta un valor de 4 x 10ˉ5. Como contrapartida, el ion molecular 26AlOˉ sufre la interferencia del ion isobárico 26MgOˉ. Por lo tanto, la aplicación de este método requirió la supresión del 26Mg, la cualse efectuó mediante la técnica de imán con gas y una separación química muy selectiva. Aeste fin se desarrolló un procedimiento químico que redujo la presencia de 26Mg a niveles delorden de 5 ppm en muestras de 500 μg de Al. Esta supresión de la interferencia isobárica,conjuntamente con la eficiencia de detección lograda, permite detectar la presencia de 26Alen muestras conteniendo tan sólo 10 5 átomos de este isótopo. Mediante este nuevo método se determinó la intensidad de tres resonancias de la reacción 25Mg(p,γ)). Estas resonancias, con energías E lab p = 316,1; 389,0 y 434,5 keV dominan laproducción estelar de 26Al en novas y presupernovas (0,1 GK <~ T <~ 1,5 GK). Los resultadoslos obtenidos en este trabajo coinciden con las mediciones más recientes de estas resonancias.The 25Mg(p,γ) reaction is the main mechanism for the stellar production of the radioisotope 26Al. Due to its long mean life (τ(26Al)~10 6 a) this radioisotope may escape fromits originating star and decay in the interstellar medium. The detection of the radiationgenerated by its decay allows to trace the 26Al-producing spots within the Milky Way, andhence to impose constrains on nucleosynthesis models. For this purpose, it also necessaryan accurate knowledge of the production rate of the 25Mg(p,γ)26Al 9 resonant reaction at thestellar energy range. Previous to this work, the resonance strenghts of this reaction were determined by onlinedetection of the prompt gamma-ray from the deexcitation of the compound nucleus 26Al. However, at stellar energies, far below the Coulomb barrier, the reaction has an extremelylow production rate and its measurement is hindered by room gamma background andbackground produced by reactions on contaminating elements. To overcome this hindrance, in this work an alternative method based on the high sensitivityof the accelerator mass spectrometry (AMS) was developed. In this method, MgOtargets are proton-bombarded (in amounts of 10 19)at each resonance energy. Subsequently,these targets are chemically treated, adding and homogenizing a well-determined amountof the stable 27Al isotope and eliminating the original Mg from the sample. The samplesgenerated in this way contain the 26Al produced in the p + 25Mg reaction, and their amountis determined measuring the 26Al/27Al concentration by means of the AMS technique. The small amount of 26Al contained in the samples (in the order of 10 6 - 10 7 atoms) requiredan optimization of the detection efficiency. To this end, concentration measurementson samples were done extracting molecular 26AlOˉ from them. The use of the molecular ion,about 25 times more prolific than the commonly-used atomic Alˉ ion, yielded an improvementin the detection efficiency up to a value of 4 x 10ˉ5. However, the molecular ion 26AlOˉ suffers the drawback of 26MgOˉ interference. Therefore,this method requires the suppression of the 26Mg isobar, which was achieved by meansof a gas-filled magnet and a highly selective chemical separation. To this end, a chemical procedurewas developed which is capable of suppressing 26Mg down to contamination levels ofabout 5 ppm from small (500 μg) Al samples. This background suppression, combined withthe achieved detection efficiency, allows to trace 26Al nuclei in samples containing amountsdown to 10 5 atoms of this isotope. By means of this new method, the strength of three resonances of the reaction 25Mg(p,γ)were determined. These resonances, with energies of E lab p = 316.1, 389.0 and 434.5 keV, dominatethe stellar production of 26Al in novae and presupernovae (0.1 GK <~ T <~ 1.5 GK). Results obtained in this work agree with most recently obtained values for these resonances.Fil: Arazi, Andrés. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina