Multipole modes in deformed nuclei within the finite amplitude method

TL;DR

This paper introduces a fast, self-consistent finite amplitude method (FAM) framework for computing QRPA transition strengths in deformed nuclei, enabling efficient global nuclear structure studies.

Contribution

The authors develop and implement a fully self-consistent FAM-QRPA method for deformed nuclei, allowing rapid calculation of multipole transition strengths without quasiparticle space truncation.

Findings

Demonstrated feasibility with calculations in $^{240}$Pu and $^{154}$Sm.

Enabled computation of the entire strength function for deformed nuclei.

Facilitates large-scale surveys of nuclear excitations and beta decay properties.

Abstract

Background: To access selected excited states of nuclei, within the framework of nuclear density functional theory, the quasiparticle random phase approximation (QRPA) is commonly used. Purpose: We present a computationally efficient, fully self-consistent framework to compute the QRPA transition strength function of an arbitrary multipole operator in axially-deformed superfluid nuclei. Methods: The method is based on the finite amplitude method (FAM) QRPA, allowing fast iterative solution of QRPA equations. A numerical implementation of the FAM-QRPA solver module has been carried out for deformed nuclei. Results: The practical feasibility of the deformed FAM module has been demonstrated. In particular, we calculate the quadrupole and octupole strength in a heavy deformed nucleus $^{240}$Pu, without any truncations in the quasiparticle space. To demonstrate the capability to calculate individual QRPA modes, we also compute low-lying negative-parity collective states in $^{154}$Sm. Conclusions: The new FAM implementation enables calculations of the QRPA strength function throughout the nuclear landscape. This will facilitate global surveys of multipole modes and beta decays, and will open new avenues for constraining the nuclear energy density functional.