Nuclear Theory·nucl-th

Thursday·July 20, 2017

5 papers—4 primary·1 cross-listed

01
[Submitted on 19 Jul 2017]
Elastic $α$ - $^{12}$ C scattering at low energies with the bound states of $^{16}$ O in effective field theory
Shung-Ichi Ando (Sunmoon U.)
The elastic $α$ - $^{12}$ C scattering for $l = 0, 1, 2, 3$ channels at low energies is studied, including the energies of excited bound states of $^{16}$ O, in effective field theory. We introduce a new renormalization method due to the large suppression factor produced by the Coulomb interaction when fitting the effective range parameters to the phase sift data. After fitting the parameters, we calculate asymptotic normalization constants of the $0_{2}^{+}$ , $1_{1}^{-}$ , $2_{1}^{+}$ , $3_{1}^{-}$ states of $^{16}$ O. We also discuss the uncertainties of the present study when the amplitudes are interpolated to the stellar energy region of the $^{12}$ C( $α$ , $γ$ ) $^{16}$ O reaction.
Comments:
18 pages, 10 eps figures, version accepted for publication in Phys. Rev. C
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1707.05920 [pdf]
PRC(2018)·33 citations
02
[Submitted on 19 Jul 2017]
Astrophysical $^{3} He (α, γ)^{7} Be$ and $^{3} H (α, γ)^{7} Li$ direct capture reactions in a potential model approach
E.M. Tursunov · S.A. Turakulov · A.S. Kadyrov
The astrophysical $^{3} He (α, γ)^{7} Be$ and $^{3} H (α, γ)^{7} Li$ direct capture processes are studied in the framework of the two-body model with the potentials of a simple Gaussian form, which describe correctly the phase-shifts in the s-, p-, d-, and f-waves, as well as the binding energy and the asymptotic normalization constant of the ground $p_{3/2}$ and the first excited $p_{1/2}$ bound states. It is shown that the E1-transition from the initial s-wave to the final p-waves is strongly dominant in both capture reactions. On this basis the s-wave potential parameters are adjusted to reproduce the new data of the LUNA collaboration around 100 keV and the newest data at the Gamov peak estimated with the help of the observed neutrino fluxes from the Sun, $S_{34}$ (23 $_{- 5}^{+ 6}$ keV)=0.548 $\pm$ 0.054 keV b for the astrophysical S-factor of the capture process $^{3} He (α, γ)^{7} Be$ . The resulting model describes well the astrophysical S-factor in low-energy Big Bang nucleosynthesis region of 180-400 keV, however has a tendency to underestimate the data above 0.5 MeV. Two-body potentials, adjusted on the properties of the $^{7}$ Be nucleus, $^{3} He + α$ elastic scattering data and the astrophysical S-factor of the $^{3} He (α, γ)^{7} Be$ direct capture reaction, are able to reproduce the properties of the $^{7}$ Li nucleus, the binding energies of the ground 3/2 $^{-}$ and first excited 1/2 $^{-}$ states, and phase shifts of the $^{3} H + α$ elastic scattering in partial waves. Most importantly, these potential models can successfully describe both absolute value and energy dependence of the existing experimental data for the mirror astrophysical $^{3} H (α, γ)^{7} Li$ capture reaction without any additional adjustment of the parameters.
Comments:
22 pages, 8 figures, 2 tables
Subjects:
Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR)
arXiv:
1707.05948 [pdf]
PRC(2018)·19 citations
03
[Submitted on 19 Jul 2017]
Thermal decay of a metastable state: the influence of the re-scattering on the quasistationary dynamical rate
Maria Chushnyakova · Igor Gontchar
When a Brownian particle, initially being in the potential well, overcomes the barrier and moves to the absorptive border, it still has a chance to be scattered back to the well by thermal fluctuations. We study this phenomenon carefully modeling numerically the motion of the particle with the Langevin equations. Four potentials which coincide near the well and the barrier but differ in the tail (i.e. beyond the barrier) are considered. It is shown that the potential for which the well and the barrier are described by two smoothly joined parabolas ("the parabolic potential") plays a role of a dividing range for the mutual layout of the quasistationary dynamical rate and the widely used in the literature Kramers rate. Namely, for the potentials with a steeper tails, the Kramers rate R_K0 underestimates the true quasistationary dynamical rate R_D, whereas for the less steep tails opposite holds (inversion of R_D/R_K0). It is proved that the mutual layout of the values of the R_D for different potentials is explained by the re-scattering of the particles from the potential tail.
Comments:
13 pages, 5 figures, 1 table
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1707.06046 [pdf]
PRE(2018)·6 citations
04
[Submitted on 19 Jul 2017]
Low-lying electric-dipole strengths of Ca, Ni, and Sn isotopes imprinted on total reaction cross sections
W. Horiuchi · S. Hatakeyama · S. Ebata · Y. Suzuki
Low-lying electric-dipole ( $E 1$ ) strength of a neutron-rich nucleus contains information on neutron-skin thickness, deformation, and shell evolution. We discuss the possibility of making use of total reaction cross sections on $^{40}$ Ca, $^{120}$ Sn, and $^{208}$ Pb targets to probe the $E 1$ strength of neutron-rich Ca, Ni, and Sn isotopes. They exhibit large enhancement of the $E 1$ strength at neutron number $N > 28$ , $50$ , and $82$ , respectively, due to a change of the single-particle orbits near the Fermi surface participating in the transitions. The density distributions and the electric-multipole strength functions of those isotopes are calculated by the Hartree-Fock+BCS and the canonical-basis-time-dependent-Hartree-Fock-Bogoliubov methods, respectively, using three kinds of Skyrme-type effective interaction. The nuclear and Coulomb breakup processes are respectively described with the Glauber model and the equivalent photon method in which the effect of finite-charge distribution is taken into account. The three Skyrme interactions give different results for the total reaction cross sections because of different Coulomb breakup contributions. The contribution of the low-lying $E 1$ strength is amplified when the low-incident energy is chosen. With an appropriate choice of the incident energy and target nucleus, the total reaction cross section can be complementary to the Coulomb excitation for analysing the low-lying $E 1$ strength of unstable nuclei.
Comments:
12 pages, 6 figures, to appear in Phys. Rev. C
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1707.06072 [pdf]
PRC(2017)·13 citations

Affiliations

first authorsco-authorsvia INSPIRE

Elastic α-12C scattering at low energies with the bound states of 16O in effective field theory

Astrophysical 3He(α,γ)7Be and 3H(α,γ)7Li direct capture reactions in a potential model approach

Thermal decay of a metastable state: the influence of the re-scattering on the quasistationary dynamical rate

Low-lying electric-dipole strengths of Ca, Ni, and Sn isotopes imprinted on total reaction cross sections

Affiliations

Elastic $α$ - $^{12}$ C scattering at low energies with the bound states of $^{16}$ O in effective field theory

Astrophysical $^{3} He (α, γ)^{7} Be$ and $^{3} H (α, γ)^{7} Li$ direct capture reactions in a potential model approach