34 research outputs found
Amphibole: A major carrier of helium isotopes in crustal rocks
The first evidence for a specific role of amphiboles in He isotope balance of crustal rocks was presented in early contributions by Gerling et al. (1971, 1976). Since then it was shown that 4He and 3He concentrations in amphiboles generally exceed those in the host rock samples. Recently amphibole was considered as an important carrier of noble gases and other volatiles components in the course of their subduction into the mantle. This paper presents new data on the balance and mobility of noble gas isotopes and major gas constituents in amphibole separates in order to understand sources and evolution of volatile components of 2666 Ma old alkaline granites from Ponoy massif (Kola Peninsula), which underwent metamorphism 1802 Ma ago.In the amphiboles 3He, 4He and 40Ar* were dominantly produced in situ due to radioactive decay of the parent isotopes and associated nuclear reactions. A small fraction of He (â 3% of the total) is liberated by crushing and shows 3He/4He ratio indistinguishable from that found by total extraction. The fraction of trapped 40Ar* amounts to â 40%; both these fractions presumably occupy fluid inclusions and show rather low 4He/40Ar* â 0.1, a factor of â 150 below the production ratio (calculated assuming no loss / gain of the species has happened since the time of metamorphism).3He has been better preserved in amphiboles compared with 4He: the retention parameter (measured amount of He / totally produced amount) for 3He (â 0.4) exceeds that for 4He (â 0.15).He extraction by fast and slow linear heating of amphiboles resulted in different release patterns. The fast heating (within 12 to 40 °C minâ 1) revealed a superposition of two peaks. When heating with slower heating rate (below 8 °C minâ 1) was applied, the high-temperature peak disappeared (the âdisappearing siteâ). Extractions of He atoms from grain and powder samples at different heating rates have shown that: (1) the âdisappearing siteâ is revealed by the fast heating analyses of different amphibole samples but not only those from the Ponoy massif; (2) amount of He liberated from the âdisappearing siteâ is variable and generally much less than the total amount of He in the sample; (3) analysis of the powder produced in the crushing experiments never reveals the âdisappearing siteâ; the temperature of He release from the powder is lower than that from the mm grain size sample by â 50 °C. Possible explanations of the nature of the âdisappearing siteâ are discussed. However, independently on nature of this effect, repeated gas extractions by heating at different rates would give additional information about structure and its transformation during heating of amphiboles.The simplest explanation of the observed abundances of noble gas isotopes in the amphibole separates from Ponoy granites suggests local production, redistribution and partial loss of noble gases during evolution of the massif
Sub- and above barrier fusion of loosely bound Li with Si
Fusion excitation functions are measured for the system Li+Si
using the characteristic -ray method, encompassing both the sub-barrier
and above barrier regions, viz., = 7-24 MeV. Two separate experiments
were performed, one for the above barrier region (= 11-24 MeV) and
another for the below barrier region (= 7-10 MeV). The results were
compared with our previously measured fusion cross section for the
Li+Si system. We observed enhancement of fusion cross section at
sub-barrier regions for both Li and Li, but yield was substantially
larger for Li. However, for well above barrier regions, similar type of
suppression was identified for both the systems.Comment: 8 pages, 6 figures, as accepted for publication in Eur.Phys.J.
Study of doubly strange systems using stored antiprotons
Bound nuclear systems with two units of strangeness are still poorly known despite their importance for many strong interaction phenomena. Stored antiprotons beams in the GeV range represent an unparalleled factory for various hyperon-antihyperon pairs. Their outstanding large production probability in antiproton collisions will open the floodgates for a series of new studies of systems which contain two or even more units of strangeness at the PâŸANDA experiment at FAIR. For the first time, high resolution Îł-spectroscopy of doubly strange ÎÎ-hypernuclei will be performed, thus complementing measurements of ground state decays of ÎÎ-hypernuclei at J-PARC or possible decays of particle unstable hypernuclei in heavy ion reactions. High resolution spectroscopy of multistrange Îâ-atoms will be feasible and even the production of Ωâ-atoms will be within reach. The latter might open the door to the |S|=3 world in strangeness nuclear physics, by the study of the hadronic Ωâ-nucleus interaction. For the first time it will be possible to study the behavior of ÎâŸ+ in nuclear systems under well controlled conditions