Effects of Non-nucleonic Degrees of Freedom in theD(p→,γ)H3

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 ...

EXAMINATION OF THE ASTROPHYSICAL S-FACTORS OF THE RADIATIVE PROTON CAPTURE ON 2H, 6Li, 7 Li, 12C AND 13C

“…33 S 0 =0.216(6) eV b and S 1 =0.0059(4) eV b keV -1 , that are noticeably differ from the data of work Schimd et al 32 The other known results for the S-factor obtained from the experimental data, without separation to M1 and E1 parts yield for zero energy 0.165(14) eV b. 41 The previous measurements of the same authors lead to the value 0.121(12) eV b, 42 and for theoretical calculations of work Viviani et al 43 the values S s =0.105 eV b, S р =0.0800-0.0865 eV b are obtained for different models.…”

Thermonuclear processes for three body system in the potential cluster model

“…In this paper the following parameters of linear extrapolation (34) are given: S 0 = 0.216(6) eV b and S 1 = 0.0059(4) eV b keV -1 , which noticeably differ from the data of [47]. The other known results for the S-factor obtained from experimental data without separation into M1 and E1 parts yield for zero energy 0.165 (14) eV b [59]. Previous results of the same authors yield 0.121(12) eV b [60], and in theoretical calculations [61] the following values were obtained for different models: S s (0) = 0.105 eV b and S р (0) = 0.08-0.0865 eV b and the total S-factor equals to 0.185-0.192 eV b.…”

Frontiers in nuclear astrophysics

“…Once deuterium is produced in the Sun, it is promptly consumed by a nonresonant direct capture reaction to the ground state of 3 He, d + p → 3 He + γ, with a Q-value of 5.5 MeV and the S-factor at zero energy is S(0) = 0.214 +0.017 −0.016 eV b according to Ref. [207] based on a combination of fits to experimental data [74,313,78,79] and theory [83]. Notice that the deuteron induced reactions d(d, p)t, d(d, n) 3 He, d( 3 He, p) 4 He, and d( 3 He, γ) 5 Li (34) have a larger cross section than that for d(p,γ) 3 He.…”