Measurement of the 25Mg(p,γ)26Al reaction at stellar energies

Stellar nuclear reactions, generally occurring at energies well below the Coulomb barrier, have extremely low cross sections posing a very difficult task for their determination using the usual prompt γ-ray detection method. We describe here the application of the highly sensitive Accelerator Mass Spectrometry technique (AMS) as an alternative method for the determination of the resonance strengths of the ²⁵Mg(p,γ) reaction, by off-line counting of the produced ²⁶Al nuclei.     

Calcium-aluminum-rich inclusion found in the Ivuna CI chondrite: Are CI chondrites a good proxy for the bulk composition of the solar system?

Cosmochemists have relied on CI carbonaceous chondrites as proxies for chemical composition of the non-volatile elements in the solar system because these meteorites are fine-grained, chemically homogeneous, and have well-determined bulk compositions that agree with that of the solar photosphere, within uncertainties. Here we report the discovery of a calcium-aluminum-rich inclusion (CAI) in the Ivuna CI chondrite. CAIs are chemically highly fractionated compared to CI composition, consisting of refractory elements and having textures that either reflect condensation from nebular gas or melting in a nebular environment. The CAI we found is a compact type A CAI with typical ¹⁶O-rich oxygen. However, it shows no evidence of ²⁶Al, which was present when most CAIs formed. Finding a CAI in a CI chondrite raises serious questions about whether CI chondrites are a reliable proxy for the bulk composition of the solar system. Too much CAI material would show up as mismatches between the CI composition and the composition of the solar photosphere. Although small amounts of refractory material have previously been identified in CI chondrites, this material is not abundant enough to significantly perturb the bulk compositions of CI chondrites. The agreement between the composition of the solar photosphere and CI chondrites allows no more than ~0.5 atom% of CAI-like material to have been added to CI chondrites. As the compositions of CI chondrites, carbonaceous asteroids, and the solar photosphere are better determined, we will be able to reduce the uncertainties in our estimates of the composition of the solar system.     

Strong screening effects on resonant nuclear reaction ~(23)Mg(p,γ) ~(24)Al in the surface of magnetars

Based on the theory of relativistic superstrong magnetic fields(SMFs), by using the method of Thomas-Fermi-Dirac approximations, we investigate the problem of strong electron screening(SES) in SMFs and the influence of SES on the nuclear reaction of ~(23)Mg(p,γ)~(24)Al. Our calculations show that the nuclear reaction will be markedly effected by the SES in SMFs in the surface of magnetars. Our calculated screening rates can increase two orders of magnitude due to SES in SMFs.     

Revisiting the radiation history of fossil meteorites from Sweden (Rebuttal to a comment by Wieler et al. On the paper by V.A. Alexeev “Radiation History of Fossil Meteorites from Sweden,” published in solar system research, 44, 311–319)

From the analysis of the data acquired for the chromite grains recovered from fossil meteorites from Sweden (Heck et al., 2004, 2008), the dependence of the exposure age of meteorites on a mass of the examined samples was obtained (Alexeev, 2010). This dependence, whatever its nature, puts into question the validity of the conclusion on a long lasting (over the course of 1–2 Myr) and substantial (by 1–2 orders of magnitude) increase in the intensity of the flux of meteorites (L-chondrites) that fell onto the Earth about 470 Myr ago. All of the fossil meteorites found in southern Sweden could be the fragments of a single meteorite that fell as a meteorite shower in the Thorsberg quarry region ∼470 Myr ago.     

Spacecraft Equipped with a Space Debris Removal System (Aerothermodynamics,Bulk–Mass Characteristics and Trajectories of Spacecraft Descent from Near-Earth Orbits)

The processes of space debris formation are described; the urgency of the problem of its removal from near-Earth space is noted. A method to prevent the clogging of space by equipping a spacecraft to be launched into orbit with additional devices, simple in design and mode of operation, is presented. The results of the estimation of aerothermodynamics, bulk–mass characteristics and trajectories of low-orbit spacecraft equipped with a space debris disposal system are presented.     

A flux enhancement measured in energetic particles(E ∼ 60–100 keV) by the epona instrument aboard Giotto close to P⧸Grigg-Skjellerup,and its interpretationas the signature of a companion comet

A significant flux enhancement in energetic particles (E ∼ 60–⩾260 keV),showing internal fine structure interpreted to represent signatures produced during the traversalof various cometary boundaries in P⧸Grigg-Skjellerup, was recorded by the EPONA instrumentaboard spacecraft Giotto on 10 July 1992. A further internally structured flux enhancement withabout the same amplitude, recorded by EPONA in the energy range ∼60–100 keV but detected90×10³ km further on along the Giotto trajectory, is herein compared with theP⧸Grigg-Skjellerup record. Possible explanations for the second flux enhancement areindividually considered and it is suggested, on the basis of the available evidence, that itconstituted the signature of another smaller comet, either having a separate genesis from, ororiginating in a splitting of, the P⧸Grigg-Skjellerup nucleus.