Nuclear Theory·nucl-th

Wednesday·January 26, 2022

9 papers—4 primary·5 cross-listed

01
[Submitted on 24 Jan 2022]
Universal Properties of Weakly Bound Two-Neutron Halo Nuclei
Masaru Hongo🇺🇸 · Dam Thanh Son🇺🇸
We construct an effective field theory of a two-neutron halo nucleus in the limit where the two-neutron separation energy $B$ and the neutron-neutron two-body virtual energy $ϵ_{n}$ are smaller than any other energy scale in the problem, but the scattering between the core and a single neutron is not fine-tuned, and the Efimov effect does not operate. The theory has one dimensionless coupling which formally runs to a Landau pole in the ultraviolet. We show that many properties of the system are universal in the double fine-tuning limit. The ratio of the mean-square matter radius and charge radius is found to be $⟨ r_{m}^{2} ⟩ / ⟨ r_{c}^{2} ⟩ = A f (ϵ_{n} / B)$ , where $A$ is the mass number of the core and $f$ is a function of the ratio $ϵ_{n} / B$ which we find explicitly. In particular, when $B ≫ ϵ_{n}$ , $⟨ r_{m}^{2} ⟩ / ⟨ r_{c}^{2} ⟩ = \frac{2}{3} A$ . The shape of the the $E 1$ dipole strength function also depends only on the ratio $ϵ_{n} / B$ and is derived in explicit analytic form. We estimate that for the $^{22}$ C nucleus higher-order corrections to our theory are of order 20% or less if the two-neutron separation energy is less than 100 keV and the $s$ -wave scattering length between a neutron and a $^{20}$ C nucleus is less than 2.8 fm.
Comments:
5+6 pages, 6+5 figures; v2: typos fixed, published version
Subjects:
Nuclear Theory (nucl-th); Quantum Gases (cond-mat.quant-gas); High Energy Physics — Theory (hep-th)
arXiv:
2201.09912 [pdf]
PRL(2022)·25 citations
02
[Submitted on 24 Jan 2022]
Photoproduction of pion pairs at high energy and small angles
S. Gevorkyan🇷🇺 · I. Larin🇺🇸 · R. Miskimen🇺🇸 · E. Smith🇺🇸
We explore the photoproduction mechanisms for charged and neutral pion pairs off a heavy nucleus at threshold. We calculate the production of charged pairs in the Coulomb field of the nucleus in the Born approximation using explicit expressions for the differential cross sections and their connection with the total cross-section. The production of sigma mesons at threshold and their subsequent decay into pions is an important mechanism and is investigated quantitatively in a framework that can be used for both charged and neutral pions. Sigma mesons can be produced via electromagnetic (photon exchange) or strong (omega exchange) interactions. For neutral pions, another important production mechanism consists of the two-step process where charged pions are produced first and then charge exchange into two neutral pions. Differential and total cross sections are computed for each production mechanism.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2201.09923 [pdf]
PRC(2022)·2 citations
03
[Submitted on 25 Jan 2022]
Rare Isotope Formation in Complete Fusion and Multinucleon Transfer Reactions in Collisions of 48Ca +248Cm around Coulomb Barrier Energies
Peng-Hui Chen · Fei Niu · Xin-Xing Xu · Zu-Xing Yang · Xiang-Hua Zeng · Zhao-Qing Feng
Within the framework of the dinuclear system model, the reaction mechanisms for synthesizing target-like isotopes from Bk to compound nuclei Lv are thoroughly investigated in complete and incomplete fusion reaction of $^{48}$ Ca + $^{248}$ Cm around Coulomb barrier energies. Production cross-section of $^{292, 293}$ Lv as a function of excitation energy in fusion-evaporation reactions and target-like isotopic yields in multinucleon transfer reactions are evaluated, in which a statistical approach is used to describe the decay process of excited nuclei. The available experimental data can be reproduced well with the model reasonably. The products of all possible formed isotopes in the dynamical pre-equilibrium process for collision partners at incident energy $E_{lab}$ = 5.5 MeV/nucleon are exported, systematically. It is found that the quasi-fission fragments are dominant in the yields. The optimal pathway from the target to compound nuclei shows up along the valley of potential surface energy. The effective impact parameter of two colliding partners leading to compound nuclei is selected from head-on collision to semi-central collision with $L$ = 52 $ℏ$ . The timescale boundary between complete fusion and multinucleon transfer reactions is about 5.7 $\times 1 0^{- 21}$ s with effective impact parameters. Synthesis cross-section of unknown neutron-rich actinides from Bk to Rf have been predicted around several nanobarns.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2201.10077 [pdf]
PRC(2022)·4 citations
04
[Submitted on 25 Jan 2022]
Operator overlaps in harmonic oscillator bases with different oscillator lengths
L.M. Robledo🇪🇸
We apply a formalism recently developed to carry out Generator Coordinate Method calculations using a set of Hartree- Fock- Bogoliubov wave functions, where each of the members of the set can be expanded in an arbitrary basis. In this paper it is assumed that the HFB wave functions are expanded in Harmonic Oscillator (HO) bases with different oscillator lengths. General expressions to compute the required matrix elements of arbitrary operators are given. The application of the present formalism to the case of fission is illustrated with an example.
Comments:
9 pages, 3 figures
Subjects:
Nuclear Theory (nucl-th); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
arXiv:
2201.10486 [pdf]
PRC(2022)·10 citations

Affiliations

first authorsco-authorsvia INSPIRE

Universal Properties of Weakly Bound Two-Neutron Halo Nuclei

Photoproduction of pion pairs at high energy and small angles

Rare Isotope Formation in Complete Fusion and Multinucleon Transfer Reactions in Collisions of 48Ca +248Cm around Coulomb Barrier Energies

Operator overlaps in harmonic oscillator bases with different oscillator lengths

Affiliations