Elastic photonuclear cross sections for bremsstrahlung from relativistic ions

TL;DR

This paper develops a method to calculate bremsstrahlung spectra for relativistic ions in ultraperipheral collisions, using the Weizs"acker-Williams method and a novel approach to estimate elastic photon scattering cross sections for various nuclei.

Contribution

It introduces a universal procedure to estimate elastic photon scattering cross sections for all nuclei with Z≥6, extending the applicability of bremsstrahlung calculations beyond existing data limitations.

Findings

Bremsstrahlung spectrum peaks at 2γ times the giant dipole resonance energy.

A new method to estimate elastic scattering cross sections using optical theorem and dispersion relations.

Procedure applicable for all Z≥6 ions with available absorption data at moderate to high energies.

Abstract

In this paper, we provide a procedure to calculate the bremsstrahlung spectrum for virtually any relativistic bare ion with charge 6$e$ or beyond, $Z\ge 6$, in ultraperipheral collisions with target nuclei. We apply the Weizs\"{a}cker-Williams method of virtual quanta to model the effect of the distribution of nuclear constituents on the interaction of the ion with the radiation target. This leads to a bremsstrahlung spectrum peaking at $2\gamma$ times the energy of the giant dipole resonance ($\gamma$ is the projectile energy in units of its rest energy). A central ingredient in the calculation is the cross section for elastic scattering of photons on the ion. This is only available in the literature for a few selected nuclei and, usually, only in a rather restricted parameter range. Hence we develop a procedure applicable for all $Z\geq6$ to estimate the elastic scattering. The elastic cross section is obtained at low to moderate photon energies, somewhat beyond the giant dipole resonance, by means of the optical theorem, a dispersion relation, and data on the total absorption cross section. The cross section is continued at higher energies by invoking depletion due to loss of coherence in the scattering. Our procedure is intended for any ion where absorption data is available and for moderate to high energies, $\gamma \gtrsim 10$.