Electromagnetic strength of neutron and proton single-particle halo nuclei

Abstract

Electromagnetic strength functions of halo nuclei exhibit universal features that can be described in terms of characteristic scale parameters. For a nucleus with nucleon+core structure the reduced transition probability, as determined, e.g., by Coulomb dissociation experiments, shows a typical shape that depends on the nucleon separation energy and the orbital angular momenta in the initial and final states. The sensitivity to the final-state interaction (FSI) between the nucleon and the core can be studied systematically by varying the strength of the interaction in the continuum. In the case of neutron+core nuclei analytical results for the reduced transition probabilities are obtained by introducing the effective-range expansion. The scaling with the relevant parameters is found explicitly. General trends are observed by studying several examples of neutron+core and proton+core nuclei in a single-particle model assuming Woods-Saxon potentials. Many important features of the neutron halo case can be obtained from a square-well model. Rather simple analytical formulas are found. The nucleon-core interaction in the continuum affects the determination of astrophysical S factors at zero energy in the method of asymptotic normalisation coefficients (ANC). It is also relevant for the extrapolation of radiative capture cross sections to low energies.

Leading E1 and M1 contributions to radiative neutron capture on lithium-7

“…The main assumption of the approach is a single-particle approximation somewhat similar to models like refs. [12][13][14]24], where the valence nucleon interacts with the core via a Woods-Saxon potential. In halo EFT, however, a systematic and model-independent expansion of observables is achieved through the use of an expansion parameter -formed by the ratio of a soft scale Q, associated with the shallowness of the valence neutron, and a hard scale Λ, related to the tightness of the core.…”

Structural effects of Na34 in the Na33(n,γ)NaSingh1, Shubhchintak2, Chatterjee3 2017Phys. Rev. C10060View full textAdd to dashboardCite

“…15 of Ref. [49]). This is not a problem with our post form theory as it includes the target-fragment electromagnetic interaction to all orders as well as the entire non-resonant continuum for all multipoles.…”

Role of higher multipole excitations in the electromagnetic dissociation of one-neutron halo nuclei

“…[7,8] in this extreme single-particle picture the total integrated B(E1) is connected to the mean square radius, r, of the single-particle state, namely [7]:…”

“…8), predicted by the simple analytical model (section 2.2) fits quite well, while at low binding energy we see some deviation from the 1/S n curve (see Refs. [7,8]). …”