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Title: {sup 26}Al production: The Allende meteorite (Chihuahua) stellar nucleosynthesis and solar models

Abstract

In 1969 a meteorite fell near the small town of Allende, state of Chihuahua in the north of Mexico. Its study yielded information that changed the current understanding of the solar model. In particular traces of {sup 26}Al were found. Abundances of that isotope had been seen in the universe and were related to regions of active heavy nucleosynthesis. Its presence on the solar system was unexpected. It is now understood that cosmic rays induce nuclear reactions on materials to produce {sup 26}Al, on Earth this is well known and it is the basis of many environmental studies, so it is not only the product of some high metalicity star collapse. Taking advantage of the recently reinforced laboratory infrastructure of the Instituto de Física, at UNAM in Mexico City, we proposed to measure the cross section for {sup 26}Al production via some of the most likely reactions, from the nuclear physics point of view (highest Q-values). In this paper the study of the {sup 28}Si(d,α){sup 26} Al nuclear reaction is shown. A target is prepared by a mixture of silicon and aluminum powders. It is irradiated with a deuteron beam (≈1 µA current) at the MV CN-Van de Graaff accelerator laboratory.more » The number of projectiles is deduced by Rutherford Backscattering Spectrometry (RBS). The produced {sup 26}Al nuclei are then counted at the Accelerator Mass Spectrometry Laboratory.« less

Authors:
; ; ; ; ; ; ; ; ;  [1]
  1. Instituto de Física, UNAM (Mexico)
Publication Date:
OSTI Identifier:
22488692
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1671; Journal Issue: 1; Conference: 11. international symposium on radiation physics, Ciudad Juarez (Mexico), 4-6 Mar 2015; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; ALPHA PARTICLES; ALUMINIUM 26; CROSS SECTIONS; DEUTERON BEAMS; DEUTERON REACTIONS; IRRADIATION; MASS SPECTROSCOPY; METEORITES; MEXICO; NUCLEAR REACTION YIELD; NUCLEOSYNTHESIS; Q-VALUE; RUTHERFORD BACKSCATTERING SPECTROSCOPY; SILICON 28; SILICON 28 TARGET; SOLAR SYSTEM; STAR MODELS; VAN DE GRAAFF ACCELERATORS

Citation Formats

Araujo-Escalona, V., Andrade, E., Barrón-Palos, L., Canto, C., Favela, F., Huerta, A., Lucio, O. de, Ortiz, M. E., Solís, C., and Chávez, E., E-mail: chavez@fisica.unam.mx. {sup 26}Al production: The Allende meteorite (Chihuahua) stellar nucleosynthesis and solar models. United States: N. p., 2015. Web. doi:10.1063/1.4927192.
Araujo-Escalona, V., Andrade, E., Barrón-Palos, L., Canto, C., Favela, F., Huerta, A., Lucio, O. de, Ortiz, M. E., Solís, C., & Chávez, E., E-mail: chavez@fisica.unam.mx. {sup 26}Al production: The Allende meteorite (Chihuahua) stellar nucleosynthesis and solar models. United States. doi:10.1063/1.4927192.
Araujo-Escalona, V., Andrade, E., Barrón-Palos, L., Canto, C., Favela, F., Huerta, A., Lucio, O. de, Ortiz, M. E., Solís, C., and Chávez, E., E-mail: chavez@fisica.unam.mx. Thu . "{sup 26}Al production: The Allende meteorite (Chihuahua) stellar nucleosynthesis and solar models". United States. doi:10.1063/1.4927192.
@article{osti_22488692,
title = {{sup 26}Al production: The Allende meteorite (Chihuahua) stellar nucleosynthesis and solar models},
author = {Araujo-Escalona, V. and Andrade, E. and Barrón-Palos, L. and Canto, C. and Favela, F. and Huerta, A. and Lucio, O. de and Ortiz, M. E. and Solís, C. and Chávez, E., E-mail: chavez@fisica.unam.mx},
abstractNote = {In 1969 a meteorite fell near the small town of Allende, state of Chihuahua in the north of Mexico. Its study yielded information that changed the current understanding of the solar model. In particular traces of {sup 26}Al were found. Abundances of that isotope had been seen in the universe and were related to regions of active heavy nucleosynthesis. Its presence on the solar system was unexpected. It is now understood that cosmic rays induce nuclear reactions on materials to produce {sup 26}Al, on Earth this is well known and it is the basis of many environmental studies, so it is not only the product of some high metalicity star collapse. Taking advantage of the recently reinforced laboratory infrastructure of the Instituto de Física, at UNAM in Mexico City, we proposed to measure the cross section for {sup 26}Al production via some of the most likely reactions, from the nuclear physics point of view (highest Q-values). In this paper the study of the {sup 28}Si(d,α){sup 26} Al nuclear reaction is shown. A target is prepared by a mixture of silicon and aluminum powders. It is irradiated with a deuteron beam (≈1 µA current) at the MV CN-Van de Graaff accelerator laboratory. The number of projectiles is deduced by Rutherford Backscattering Spectrometry (RBS). The produced {sup 26}Al nuclei are then counted at the Accelerator Mass Spectrometry Laboratory.},
doi = {10.1063/1.4927192},
journal = {AIP Conference Proceedings},
number = 1,
volume = 1671,
place = {United States},
year = {Thu Jul 23 00:00:00 EDT 2015},
month = {Thu Jul 23 00:00:00 EDT 2015}
}
  • Recent nuclear reaction studies on /sup 26/Al have established the existence of a previously unobserved s-wave resonance in the /sup 25/Mg+p system at E/sub cm/ = 37.2 keV and a possible resonance at E/sub cm/ = = 94.0 keV. The /sup 25/Mg(p, ..gamma..)/sup 26/Al reaction rate has been calculated for temperatures characteristic of both nonexplosive and explosive hydrogen burning, and the astrophysical consequences of the 37.2 keV and 94.0 keV resonances are discussed; it is demonstrated that the contributions of these resonances increase the reaction rate by 10 orders of magnitude at stellar temperatures near T/sub 9/ = 0.04.
  • Twenty-six Al{sub 2}O{sub 3} grains from the Murchison CM2 chondrite have been analyzed by ion microprobe mass spectrometry for the isotopes of O, Mg, and Ti and the abundances of Mg, Ca, Sc, Ti, V, Sr, Y, Zr, La, and Ce. Being the most refractory major phase in solar matter, Al{sub 2}O{sub 3} retains a particularly durable record of the early solar system. {sup 26}Mg/{sup 24}Mg ranges up to 56{times} the solar-system ratio, owing to decay of extinct {sup 26}Al, but the initial {sup 26}Al/{sup 27}Al ratios do not exceed the canonical maximum of 5 {times} 10{sup {minus}5} established inmore » earlier work. There is no evidence for fossil radiogenic {sup 26}Mg surviving from presolar times. Oxygen isotope compositions cluster mainly near {delta}{sup 18}O = {minus}50%, but range from {minus}94 to {minus}11{per thousand}. The grains divide into three groups on the basis of {sup 26}Al, {sup 16}O, Ti and V content, and {sup 26}Al and O show distinctive correlations, suggesting an origin from the following components. Group 1 (high {sup 26}Al, Ti, V): mixture of material with {sup 26}Al/{sup 27}Al = 5 {times} 10{sup {minus}5} and {delta}{sup 18}O = {minus}45{per thousand} with dead Al of {delta}{sup 18}O {approx} {minus}100{per thousand}. Group 2 (low {sup 26}Al, Ti, V): mixture of material with {sup 26}Al/{sup 27}Al = 5 {times} 10{sup {minus}6} with dead Al, with complex fractionation and exchange of O resembling that of FUN inclusions. Group 3 (no {sup 26}Al; high Ti, V): dead Al from various sources. In terms of this model, the corundum formed from two components with live {sup 26}Al and a mass fraction of 43% dead Al, but the authors do not know whether this figure is typical of carbonaceous chondrites in toto, let alone the entire solar nebula. Trace element abundances in corundum are generally at less than Cl levels relative to Al, and decline with increasing volatility, from Zr to Ca.« less
  • The authors have studied a suite of six coarse-grained Ca-Al-rich inclusions (CAIs) from the Allende meteorite, applying in concert detailed petrographic and chemical characterization, ion probe mass spectrometric analyses of the Al-Mg isotopic system to determine the abundance and distribution of {sup 26}Al, and thermal emission mass spectrometric analyses of the Rb-Sr system to determine initial {sup 87}Sr/{sup 86}Sr ratios. The simplest inclusion is a Type B1, USNM 3529-Z, that shows evidence of minor alteration and recrystallization since solidification from a melt droplet. The Rb-Sr isotopic system also typically indicates some level of disturbance, some of which must have beenmore » relatively recent. Nevertheless, phases characterized by very low Rb/Sr permit precise identification of initial {sup 87}Sr/{sup 86}Sr. Our Al-Mg and Sr data are largely consistent with a simple chronological interpretation of both systems. The present data are the first which establish a firm association between primitive {sup 26}Al/{sup 27}Al and primitive {sup 87}Sr/{sup 86}Sr by analysis of both isotopic systems in the same inclusions. The comparison of both isotopic systems, interpreted as simple nebular chronometers, does not reveal any chronological inconsistencies that demand resolution in terms of a grossly heterogeneous distribution of {sup 26}Al.« less
  • The nucleosynthetic origin of {sup 26}Al (t{sub 1/2}=0.72 Myr) in the early solar system is still an open question. Several models predict that short-lived radionuclides could be produced by irradiation of circumsolar material by light charged particles emitted by the young sun. Within some models, most of the {sup 26}Al is produced by {sup 3}He-induced reactions on {sup 24}Mg. Little experimental data exist on {sup 3}He reactions so that irradiation models have had to rely on theoretical cross sections deduced from statistical nuclear reaction codes. We performed a direct measurement of the {sup 26}Al production on Mg target by meansmore » of {gamma} ray spectroscopy and accelerator mass spectrometry (AMS). The data indicate that the theoretical cross section used in previous approaches was overestimated by a factor of 3. Taking the particle spectra considered in theoretical approaches these data lead to a net reduction of the {sup 26}Al production of a factor of 2. We calculated the relative contribution of the different {sup 26}Al production channels depending on the irradiation scenario. We show that extremely large particles fluxes would be necessary to reach the canonical {sup 26}Al/{sup 27}Al =5x10{sup -5} in solids that were present in the early solar system. An in situ origin of this important isotopic chronometer by irradiation is unlikely.« less