Light elements play a key role in different scenario in astrophysics, ranging from primordial nucleosynthesis up to stellar nucleosynthesis and cosmic ray nucleosynthesis. The nuclear reaction cross ...section measurements of interest in primordial and stellar nucleosynthesis have been investigated in terrestrial laboratories via devoted experiments. However, because of the difficulties in reaching the Gamow energy windows of interest for such processes through direct approaches, the indirect Trojan Horse Method (THM) have been used in the last ’30 years for shedding light on some unsolved questions. After an introductory discussion about the role of the light elements, the discussion will be focused on the application of THM to two different case studies.
Silver nitrate reacts with 6‐methylmercaptopurine riboside (6‐MMPR) in aqueous solution containing methanol and dimethyl sulfoxide at room temperature to give a colourless crystalline complex, ...namely, bis(6‐methylmercaptopurine riboside‐κN7)(nitrato‐κ2O,O′)silver(I) 2.32‐hydrate, Ag(NO3)(C11H14N4O4S)2·2.32H2O. The crystal structure, determined from synchrotron diffraction data, shows a central AgI ion on a crystallographic twofold rotation axis, coordinated in an almost linear fashion by two 6‐MMPR ligands via atom N7 (purine numbering), with the nitrate counter‐ion loosely coordinated as a bidentate ligand, forming a discrete molecular complex as an approximate dihydrate. The complex and water molecules are connected in a three‐dimensional network by hydrogen bonding.
Silver has an almost linear primary coordination with two N‐bound 6‐methylmercaptopurine riboside ligands and a nitrate anion giving weaker secondary coordination in a bidentate mode.
Advances in bottom-up material design have been significantly progressed through DNA-based approaches. However, the routine integration of semiconducting properties, particularly long-range ...electrical conduction, into the basic topological motif of DNA remains challenging. Here, we demonstrate this with a coordination polymer derived from 6-thioguanosine (6-TG-H), a sulfur-containing analog of a natural nucleoside. The complexation reaction with Au(I) ions spontaneously assembles luminescent one-dimensional helical chains, characterized as {Au
(μ-6-TG)}
, extending many μm in length that are structurally analogous to natural DNA. Uniquely, for such a material, this gold-thiolate can be transformed into a wire-like conducting form by oxidative doping. We also show that this self-assembly reaction is compatible with a 6-TG-modified DNA duplex and provides a straightforward method by which to integrate semiconducting sequences, site-specifically, into the framework of DNA materials, transforming their properties in a fundamental and technologically useful manner.Integration of semiconducting properties into the basic topological motif of DNA remains challenging. Here, the authors show a coordination polymer derived from 6-thioguanosine that complexes with Au(I) ions to form a wire-like material that can also integrate semiconducting sequences into the framework of DNA materials.
In this work the optical properties of the formed gold nanoparticles, that obtained upon reducing the gold(I):6-thioguanosine hydrogel by dimethylamine borane (DMAB) have been studied. The analytical ...measurements to calculate the optical band gap showed a significant narrowing in the optical band gap value (Eg). Tauc plot was used to estimate the optical band gap (Eg) with the direct and indirect allowed transitions, before and after the reducing process. Narrowing the band gap is very important to increase the efficiency of the semiconductor material as it leads to absorbing in the visible region of the solar spectrum.
Gold nanoparticles; Relativistic effect; Photocatalyst; Dimethylamine borane; Hydrogen gas; Narrowing band gap.
Astrophysics studies with the Trojan Horse Method Spitaleri, C.; La Cognata, M.; Lamia, L. ...
The European physical journal. A, Hadrons and nuclei,
09/2019, Letnik:
55, Številka:
9
Journal Article
Recenzirano
.
The Trojan Horse Method represents an indirect approach to investigate reactions of astrophysical relevance at the energies of interest, free of Coulomb suppression and electron screening effects. ...In this review, we will examine how the Trojan Horse Method has evolved from the study of the quasi-free reaction mechanism. We will first present the basic features of the quasi-free reaction mechanism in the framework of the theory of direct reactions, from quasi-free scattering to quasi-free reactions processes, and its evolution towards the Trojan Horse Method with its modern theory. We will review the validity tests to assess the technique, the procedure to analyze the data and to extract the astrophysical factor. Finally, we will discuss some of the most important experimental results recently published related to nuclear astrophysics and applications.
Nuclear astrophysics and the Trojan Horse Method Spitaleri, C.; La Cognata, M.; Lamia, L. ...
The European physical journal. A, Hadrons and nuclei,
04/2016, Letnik:
52, Številka:
4
Journal Article
Recenzirano
.
In this review, we discuss the new recent results of the Trojan Horse Method that is used to determine reaction rates for nuclear processes in several astrophysical scenarios. The theory behind ...this technique is shortly presented. This is followed by an overview of some new experiments that have been carried out using this indirect approach.
Nuclear reaction rates are among the most important input for understanding primordial nucleosynthesis and, therefore, for a quantitative description of the early universe. An up-to-date compilation ...of direct cross-sections of super(2)H(d, p) super(3)H, super(2)H(d, n) super(3)He, super(7)Li(p, alpha ) super(4)He, and super(3)He(d, p) super(4)He reactions is given. These are among the most uncertain cross-sections used and input for big bang nucleosynthesis calculations. Their measurements through the Trojan Horse method are also reviewed and compared with direct data. The reaction rates and the corresponding recommended errors in this work were used as input for primordial nucleosynthesis calculations to evaluate their impact on the 2H, super(3,4)He, and super(7)Li primordial abundances, which are then compared with observations.
Electron screening in palladium Cvetinović, A.; Đeorđić, D.; Guardo, G.L. ...
Physics letters. B,
03/2023, Letnik:
838
Journal Article
Recenzirano
Odprti dostop
The electron screening effect was studied in the 1H(7Li,α)4He, 1H(19F,αγ)16O and 2H(19F,p)20F nuclear reactions on two different hydrogen-containing palladium foils. In one of the targets we did not ...detect a large enhancement of the cross section due to electron screening, and in the second one we measured a high electron screening potential for all three reactions, up to an order of magnitude above the theoretical models. Contrary to the predictions given by the available theories, the data suggest that the reason behind this difference is linked to a dependence of the electron screening potential on the host's crystal lattice structure and the location of the target nuclei in the metallic lattice.
The Trojan Horse Method (THM) lays its foundations on the cluster structure of light nuclei which are usually used as “Trojan horses”. Many of them were successfully employed in the last decades to ...shed light to numerous astrophysical problems. Cluster structure and dynamics also suggest a series of tests which may be performed in order to strengthen the basis of the method. Among them pole invariance was investigated for three different situations. In fact, the cross sections for the
6
Li(d,
α
)
4
He,
2
H(d,p)
3
H and
7
Li(p,
α
)
4
He binary reactions were measured for several break-up schemes and analyzed within the framework of the Plane Wave Impulse Approximation (PWIA). The indirect results extracted by using different Trojan Horse nuclei (e.g.
2
H,
3
He,
6
Li) were compared with each other as well as with direct measurements of the corresponding astrophysical reactions. The very good agreement obtained confirms the applicability of the pole approximation and of the pole invariance method, namely the independence of binary indirect cross section on the chosen Trojan Horse nucleus, at least for the cases investigated. Moreover, we can verify that the effect of using a charged or a neutral particle as a spectator implies negligible corrections consistent with the experimental errors. In addition, the dynamics of clusters inside the Trojan Horse nucleus and their fingerprints on the measured momentum distribution play a key role for THM applications. In this article we will therefore discuss also these assertions studied in different systems(
2
H,
3
He,
6
Li,
9
Be,
14
N) and in particular for the deuteron case the relative impact of
s
and
d
waves in the momentum distribution will also be examined.
PDF
