In this work, angular distribution measurements for the elastic channel were performed for the
9Be
+
12C reaction at the energies
E
Lab
=
13.0
, 14.5, 17.3, 19.0 and 21.0 MeV, near the Coulomb ...barrier. The data have been analyzed in the framework of the double folding São Paulo potential. The experimental elastic scattering angular distributions were well described by the optical potential at forward angles for all measured energies. However, for the three highest energies, an enhancement was observed for intermediate and backward angles. This can be explained by the elastic transfer mechanism.
Time scales of strongly energy damped and fast processes in light heavy-ion reactions were measured in order to investigate the dynamics involved in the collision. Particle–particle correlation ...functions at small relative momenta were measured to determine the time scale of sequential particle emission in highly excited light composite systems and the values obtained are compared to the lifetime of the compound nucleus determined by cross section fluctuations measurements. The results indicate that in the case of light nuclear systems, a drastic time scale compression is observed, independent of the inelasticity of the process, in contrast to the case of heavy systems for which the time difference between the fast and slow processes is at least 100–1000 times larger.
Direct measurements in the last decades have highlighted a new problem related to the lowering of the Coulomb barrier between the interacting nuclei due to the presence of the “electron screening” in ...the laboratory measurements. It was systematically observed that the presence of the electronic cloud around the interacting ions in measurements of nuclear reactions cross sections at astrophysical energies gives rise to an enhancement of the astrophysical S(E)-factor as lower and lower energies are explored H. Assenbaum, K. Langanke, C. Rolfs, Z. Phys.
327 (1987) 461. Moreover, at present such an effect is not well understood as the value of the potential for screening extracted from these measurements is higher than the upper limit of theoretical predictions (adiabatic limit). On the other hand, the electron screening potential in laboratory measurement is different from that occurring in stellar plasmas thus the quantity of interest in astrophysics is the so-called “bare nucleus cross section”. This quantity can only be extrapolated in direct measurements. These are the reasons that led to a considerable growth on interest in indirect measurement techniques and in particular the Trojan Horse Method (THM) G. Baur, Phys. Lett. B
178, (1986) 135; S. Cherubini et al. Ap. J.
457, (1996) 855 Results concerning the bare nucleus cross sections measurements will be shown in several cases of astrophysical interest. In those cases the screening potential evaluated by means of the THM will be compared with the adiabatic limit and results arising from extrapolation in direct measurements.
The Trojan Horse Method is a powerful indirect technique allowing one to measure the bare nucleus S(E)-factor and the electron screening potential for astrophysically relevant reactions without the ...needs of extrapolations. The case of the (p,α) reactions induced on the two boron isotopes 10,11B is here discussed in view of the recent Trojan Horse (TH) applications to the quasi-free 10,11B+2H reactions. The comparison between the TH and the low-energy direct data allowed us to determine the electron screening potential for the 11B(p,α) reaction, while preliminary results on the 10B(p,α) reaction have been extracted.
Light elements lithium, beryllium and boron (LiBeB) were used in the last years as 'possible probe' for a deeper understanding of some extra-mixing phenomena occurring in young Main-Sequence stars. ...They are mainly destroyed by (p,alpha) reactions and cross section measurements for such channels are then needed. The Trojan Horse Method (THM) allows one to extract the astrophysical S(E)-factor without the experience of tunneling through the Coulomb barrier. In this work a resume of the recent results about the 11B(p,alpha0)8Be and 10B(p,alpha)7Be reactions is shown.
Sixteen triple telescopes were developed to be used in the study of light heavy-ion nuclear reactions at the University of São Paulo Pelletron Laboratory, with the purpose of providing simultaneous ...identification of light and heavy reaction products. Each telescope consists of one ionization chamber, one Si detector and one CsI detector with photodiode readout. The telescopes are encapsulated in such a way that they can be utilized in different setup geometries depending on the kind of experiment being performed. Results for the ionization chambers energy loss resolution, Si and CsI detectors energy resolution and general performance are presented.
We report on a polarization measurement of inclusive J/ψ mesons in the di-electron decay channel at mid-rapidity at 2<pT<6 GeV/c in p+p collisions at s=200 GeV. Data were taken with the STAR detector ...at RHIC. The J/ψ polarization measurement should help to distinguish between different models of the J/ψ production mechanism since they predict different pT dependences of the J/ψ polarization. In this analysis, J/ψ polarization is studied in the helicity frame. The polarization parameter λθ measured at RHIC becomes smaller towards high pT, indicating more longitudinal J/ψ polarization as pT increases. The result is compared with predictions of presently available models.
Direct measurement of the breakup process Souza, F. A.; Liguori Neto, R.; Moura, M. M. de ...
Brazilian journal of physics,
09/2005, Volume:
35, Issue:
3b
Journal Article
Peer reviewed
Open access
In order to better understand the breakup contribution to fusion, we perfomed light particle coincidence measurements for the systems 6,7Li+12C,59Co at energies near and above the barrier. A three ...body kinematics analysis is performed with the objective of separating the contributions of different reaction mechanisms. For small angular differences between the light particles, the sequential and direct breakup seem to dominate. On the other hand, for large detector separations, a sequential decay following transfer is likely to dominate.
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