Radiative electron capture to the continuum in U89++N2 collisions: Experiment and theory

Abstract

For U 89+ projectiles colliding at a beam energy of 75.91 MeV/u with a N 2 target, we present a coincidence measurement between the cusp electrons emitted under an angle of 0 • with respect to the projectile beam and the photons emitted under a polar angle of 90 • . This radiative-electron-capture-to-continuum cusp directly probes the theory of electron-nucleus bremsstrahlung up to the high-energy endpoint in inverse kinematics. In the present study, significant improvement with respect to the experimental accuracy has been achieved, resulting in a finer agreement between experimental and theoretical results.

Electron-loss-to-continuum cusp in collisions of U$^{89+}$ with N$_{2}$ and Xe

“…2(a) and 2(b) do not comprise electrons originating from ECC. We also emphasize, that the asymmetry observed presently for the ELC with the xenon target is opposite to the asymmetry observed for the RECC process of reaction (4) measured simultaneously [21]. During the RECC process the excess energy is released by emitting a bremsstrahlung photon, therefore no momentum transfer to the target nucleus is required.…”

“…Electrons emitted from the interaction point into the forward direction were detected by the electron spectrometer within a polar acceptance angle of ϑ e = 0 • − ϑ max = 0 • − 3.3 • and the full azimuthal acceptance angle of ϕ e = 0 • − 360 • with respect to the projectile beam [21]. The electron spectrometer consisted of a sequence of a 60 • dipole magnet, an iron-free quadrupole triplet, and another 60 • dipole magnet [20].…”

“…Reaction (4) was analyzed in Ref. [21]. The electron spectrum of the RECC has a very steep rise at E 0 .…”

“…For nonrelativistic collision systems, asymmetries occurring in the ELC cusp were attributed to higher-order effects [14][15][16][17][18][19]. The advantage of the electron cusp is that the transformation of the continuum electron phase space from the projectile frame to the target frame results in a sampling of the major characteristic features along the energy axis of forward-emitted electrons [20,21]. This sampling eliminates the need to select arguable cuts of the continuum electron phase space for comparison of experiment and theory.…”

Heavy-ion storage rings and their use in precision experiments with highly charged ions

“…The need for stringent tests of its claimed relationship at the high energy end of the bremsstrahlung (BS) spectrum with other fundamental processes like photoionization, radiative recombination and pair production has been emphasized for decades by theory. Only now first experiments directed at this claim have been possible with the appearance of heavy-ion storage rings and coincidence experiments in inverse kinematics of the high energy BS photon with the associated electron from the BS elementary process [338,346,347]. More extensive studies are anticipated for the near future.…”