No abstract
Measurements of the D͑ p, g͒ 3 He and p͑ d, g͒ 3 He reactions below E p,d 80 keV are compared to the results of calculations based on correlated hyperspherical harmonic wave functions obtained from realistic interactions with full inclusion of Coulomb distortion in the initial continuum state, and a nuclear current operator with one-and two-body components. Dramatic effects due to the tensor force and the associated two-body (meson-exchange) interaction currents are observed in the vector and, to some extent, tensor analyzing powers for the first time. The extrapolation to zero energy leads to an S-factor value of S͑E 0͒ 0.165 6 0.014 eV b, in reasonable agreement with theory. [S0031-9007(96)00008-7] PACS numbers: 25.40. Lw, 21.45.+v, 24.70.+s, 27.10.+h Weak and radiative capture reactions on few-nucleon systems at very low energies have great astrophysical importance in relation to studies of stellar structure and evolution [1]. Two such aspects are as follows: (1) the mechanism for the energy and neutrino production in main sequence stars, in particular, the determination of the solar neutrino flux; and (2) the process of protostellar evolution toward the main sequence. A quantity of interest in the latter area is the zero-energy astrophysical S factor for D( p, g) 3 He, whose currently accepted value was first determined over 30 years ago by extrapolating low energy cross-section data using a direct capture model [2].Besides their astrophysical relevance, these reactions are very interesting from the aspect of the many-body theory of strongly interacting systems since they are sensitive to ground-and scattering-state wave functions and the full nuclear electroweak transition operators. Indeed, calculations of the D(n,g) 3 H and 3 He(n,g) 4 He capture cross sections at thermal neutron energies carried out with realistic wave functions and a single-nucleon electromagnetic current, the so-called impulse approximation (IA), predict only about 50% [3,4] and 10% [5] of the corresponding empirical values. This is because the IA transition operator cannot connect the main S-state components of the deuteron and 3 H, or 3 He and 4 He, wave functions. Hence, the calculated cross section in IA is small since the reaction must proceed through the small components of the wave functions. Two-body currents, however, can connect the dominant S-state components, and the associated matrix elements are exceptionally large in comparison to those obtained in IA [3][4][5].The data of this paper, some of which were reported recently [6], were obtained using a polarized proton beam at 80 keV in a study of the D͑ p, g͒ 3 He reaction, along with a tensor-polarized deuteron beam at 80 keV to measure the tensor analyzing power T 20 ͑u͒ for the p͑ d, g͒ 3 He reaction. The polarized beams were produced by the Triangle Universities Nuclear Laboratory (TUNL) atomic beam polarized ion source, with typical beam currents of 30 mA on target. Fast spin flip (10 Hz) was employed for both measurements. In the case of the vector analyzing power A ...
The excited states of aS4Gd populated by the fi-decay of lS4Eu (T1/2=8.5 y) have been studied. With a HPGe-NaI(T1) Compton suppression spectrometer and a HPGe-NaI (T1) coincidence circuit 7-ray singles spectra, coincidence spectra and the 7-7 directional correlational functions have been obtained. The deduced mixing ratios of multipolarities are presented. The energy levels and the relative B(E2) values of the various ?-transitions in XS4Gd nucleus have been calculated both in the IBA model and it's extended version with boson surface delta interaction (BSDI).
The evolution of the beam distribution in a double-rf system with a phase modulation on either the primary or secondary rf cavity was measured. We find that the particle diffusion process obeys the Einstein relation if the phase space becomes globally chaotic. When dominant parametric resonances still exist in the phase space, particles stream along the separatrices of the dominant resonance, and the beam width exhibits characteristic oscillatory structure. The particle-tracking simulations for the double-rf system are employed to reveal the essential diffusion mechanism. Coherent octupolar motion has been observed in the bunch beam excitation. The evolution of the longitudinal phase space in the octupole mode is displayed.
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