# Forward-angle electron spectroscopy in heavy-ion atom collisions studied at the ESR

P-M Hillenbrand, S. Hagmann, D Banaś, K-H Blumenhagen, C Brandau, W. Chen, E. de Filippo, A. Gumberidze, D. Guo, D. Jakubassa-Amundsen, et al.

► To cite this version:

P-M Hillenbrand, S. Hagmann, D Banaś, K-H Blumenhagen, C Brandau, et al. Forward-angle electron spectroscopy in heavy-ion atom collisions studied at the ESR. Journal of Physics: Conference Series, 2015, 635 (2), pp.022005. 10.1088/1742-6596/635/2/022005. hal-02341306

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# Forward-angle electron spectroscopy in heavy-ion atom collisions studied at the ESR

To cite this article: P-M Hillenbrand et al 2015 *J. Phys.: Conf. Ser.* **635** 022005

View the [article online](#) for updates and enhancements.

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Forward-angle electron spectroscopy in heavy-ion atom collisions studied at the ESR

P.-M. Hillenbrand<fnref n="1" />,²¹, S. Hagmann<fnref n="1" />,³², D. Banaś⁴, K.-H. Blumenhagen⁵, C. Brandau<fnref n="1" />,<fnref n="2" />, W. Chen<fnref n="1" />, E. De Filippo⁶, A. Gumberidze<fnref n="1" />, D. L. Guo⁷, D. H. Jakubassa-Amundsen⁸

M. Lestinsky<fnref n="1" />, Yu. A. Litvinov<fnref n="1" />, J. M. Monti⁹ A. Müller<fnref n="2" />, H. Rothard¹⁰, S. Schippers<fnref n="2" />, M. S. Schöffler³, U. Spillmann<fnref n="1" />, A. Surzhykov⁵, S. Trotsenko<fnref n="1" />,⁵, A. B. Voitkiv¹¹, X. L. Zhu⁸, and Th. Stöhlker<fnref n="1" />,⁵

¹GSI Darmstadt, Germany, ²Universität Giessen, Germany, ³Universität Frankfurt, Germany,

⁴JKU Kielce, Poland, ⁵Helmholtz Institut Jena, Germany, ⁶INFN Catalania, Italy, ⁷IMP Lanzhou, China,

⁸LMU München, Germany, ⁹CONICET Rosario, Argentina, ¹⁰CIMAP-CIRIL-Ganil Caen, France,

¹¹Universität Düsseldorf, Germany

**Synopsis** For the collisions system $U^{88+} + N_2$ @ 90 MeV/u the emitted cusp electrons have been studied, and the three processes contributing to the electron cusp were compared to individual theoretical calculations.

In collisions of heavy highly-charged projectile ions with atomic targets, the energy distribution of the emitted electrons is a characteristic observable for the underlying elementary processes. At the experimental storage ring ESR of the heavy-ion accelerator facility GSI, a dedicated magnetic electron spectrometer was built downstream from the gas-jet target, which enabled the measurement of high-energetic electrons emitted in ion-atom collisions within a small cone in the forward direction. Using this electron spectrometer in combination with detectors for emitted x rays and charge-exchanged projectiles, the study of the collision system $U^{88+} + N_2$ @ 90 MeV/u revealed three processes resulting in the emission of electrons with a velocity similar to the projectile velocity, i.e., cusp electrons:

(a) The process of **electron loss to continuum** (ELC) corresponds to the ionization of an electron from the projectile into the projectile continuum during the collision with the target,

$$U^{88+} + N_2 \rightarrow U^{89+} + [N_2]^* + e^-.$$

For the ELC, the measured spectrum was compared to first-order perturbation theory using fully-relativistic Dirac wavefunctions [1].

(b) The process of **electron capture to continuum** (ECC) corresponds to the capture of a target electron into the projectile continuum, while the excess energy is carried away by the recoil of the generated target ion:

$$U^{88+} + N_2 \rightarrow U^{88+} + [N_2^+]^* + e^-.$$

For the ECC, the measured spectrum was compared to calculations in the impulse approximation using semi-relativistic Sommerfeld-Maue wavefunctions, and to calculations in the continuum-distorted-wave approach [2].

(c) The process of **radiative electron capture to continuum** (RECC) corresponds to the capture of a target electron into the projectile continuum, while the excess energy is carried away by a photon:

$$U^{88+} + N_2 \rightarrow U^{88+} + [N_2^+]^* + e^- + \gamma.$$

This latter process can be seen as the high-energy endpoint of bremsstrahlung studied in inverse kinematics. For the RECC, the measured spectra were compared to calculations in the impulse approximation using semi-relativistic Sommerfeld-Maue wavefunctions, and to calculations using fully-relativistic Dirac wavefunctions [3].

Within this study it was shown that each of the three processes is characterized by a unique electron cusp shape, being a clear messenger for the underlying charge-exchange mechanism.

References

[1] P.-M. Hillenbrand et al. 2014 Phys. Rev. A 90 042713

[2] P.-M. Hillenbrand et al. 2015 Phys. Rev. A 91 022705

[3] P.-M. Hillenbrand et al. 2014 Phys. Rev. A 90 022707

<footnote n="1">¹E-mail: P.M.Hillenbrand@gsi.de</footnote>

<footnote n="2">²E-mail: S.Hagmann@gsi.de</footnote>