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Nuclear Theory·nucl-th

Monday·March 7, 2016

5 papers—3 primary·2 cross-listed

All5Primary3Cross-lists2
  1. 01

    Sensitivity of the fusion cross section to the density dependence of the symmetry energy

    P.-G. Reinhard · A.S. Umar · P.D. Stevenson · J. Piekarewicz · V.E. Oberacker · J.A. Maruhn

    It is the aim of this paper to discuss the impact of nuclear fusion on the EOS. This is a timely subject given the expected availability of increasingly exotic beams at rare isotope facilities\,\cite{balantekin2014}. In practice, we focus on Ca+Ca fusion. We employ three different approaches to calculate fusion cross-sections for a set of energy density functionals with systematically varying nuclear matter properties. Fusion calculations are performed using frozen densities, using a dynamic microscopic method based on density-constrained time-dependent Hartree-Fock (DC-TDHF) approach, as well as direct TDHF study of above barrier cross-sections. For these studies, we employ a family of Skyrme parametrizations with systematically varied nuclear matter properties. We find a slight preference for forces which deliver a slope of symmetry energy of \,MeV that corresponds to a neutron-skin thickness of Ca of \,fm.

    nucl-thPRC(2016)·42 citations
  2. 02

    Improved Algorithms and Coupled Neutron-Photon Transport for Auto-Importance Sampling Method

    Xin Wang · Zhen Wu · Rui Qiu · Chun-Yan Li · Man-Chun Liang · Hui Zhang · Jun-Li Li · Zhi Gang · Hong Xu

    The Auto-Importance Sampling (AIS) method is a Monte Carlo variance reduction technique proposed for deep penetration problems, which can significantly improve computational efficiency without pre-calculations for importance distribution. However, the AIS method is only validated with several simple examples, and cannot be used for coupled neutron-photon transport. This paper presents the improved algorithms for the AIS method, including particle transport, fictitious particles creation and adjustment, fictitious surface geometry, random number allocation and calculation of the estimated relative error. These improvements allow the AIS method to be applicable to complicated deep penetration problems with complex geometry and multiple materials. A coupled Neutron-Photon Auto-Importance Sampling (NP-AIS) method is proposed to solve the deep penetration problems of coupled neutron-photon transport using the improved algorithms. The NUREG/CR-6115 PWR benchmark was calculated by using the methods of NP-AIS, geometry splitting with Russian roulette and the analog Monte Carlo, respectively. The calculation results of NP-AIS were in good agreement with those of geometry splitting with Russian roulette and the benchmark solutions. The computational efficiency of NP-AIS for both neutron and photon was much better than that of geometry splitting with Russian roulette in most cases, and increased by several orders of magnitude compared with that of the analog Monte Carlo.

    nucl-thCPC(2017)·0 citations
  3. 03

    Uncertainty quantification for proton-proton fusion in chiral effective field theory

    B. Acharya · B. D. Carlsson · A. Ekström · C. Forssén · L. Platter

    We compute the -factor of the proton-proton () fusion reaction using chiral effective field theory (EFT) up to next-to-next-to-leading order (NNLO) and perform a rigorous uncertainty analysis of the results. We quantify the uncertainties due to (i) the computational method used to compute the cross section in momentum space, (ii) the statistical uncertainties in the low-energy coupling constants of EFT, (iii) the systematic uncertainty due to the EFT cutoff, and (iv) systematic variations in the database used to calibrate the nucleon-nucleon interaction. We also examine the robustness of the polynomial extrapolation procedure, which is commonly used to extract the threshold -factor and its energy-derivatives. By performing a statistical analysis of the polynomial fit of the energy-dependent -factor at several different energy intervals, we eliminate a systematic uncertainty that can arise from the choice of the fit interval in our calculations. In addition, we explore the statistical correlations between the -factor and few-nucleon observables such as the binding energies and point-proton radii of H and He as well as the -state probability and quadrupole moment of H, and the -decay of H. We find that, with the state-of-the-art optimization of the nuclear Hamiltonian, the statistical uncertainty in the threshold -factor cannot be reduced beyond 0.7%.

    nucl-thastro-ph.SRPLB(2016)·38 citations

Affiliations

first authorsco-authorsvia INSPIRE