Banas, D.

Blumenhagen, K.-H.

Brandau, C.

Chen, Weidong

DeFilippo, E.

Gumberidze, A.

Guo, D.

Hagmann, S.

Hillenbrand, P.-M.

Kozhuharov, C.

Lestinsky, M.

Litvinov, Y. A.

Müller, A.

Rothard, H.

Schippers, S.

Schöffler, M.

Spillmann, U.

Stöhlker, T.

Trotsenko, S.

Winckler, N.

Yan, X.

GSI Repository

Electron spectroscopy at the high-energy endpointof electron-nucleus bremsstrahlungP.-M. Hillenbrand1,2, S. Hagmann1,3, D. Banas4, C. Brandau1,5, K.-H. Blumenhagen6, W. Chen1,A. Gumberidze5, D. Guo7, E. DeFilippo8, C. Kozhuharov1, M. Lestinsky1, Y.A. Litvinov1, A. Mu¨ller2,H. Rothard9, S. Schippers2, M. Scho¨ffler3, U. Spillmann1, S. Trotsenko1,6, N. Winckler1, X. Yan7, andTh. Sto¨hlker1,61GSI Darmstadt; 2Universita¨t Giessen; 3Universita¨t Frankfurt; 4JKU, Kielce, Poland; 5EMMI Darmstadt;6Helmholtz Institut Jena; 7IMP, Lanzhou, China; 8INFN, Catalania, Italy; 9CIRIL-Ganil, Caen, FranceIn electron-nucleus bremsstrahlung an electron with ki-netic energy E0 scatters inelastically off an atomic nucleusand emits a photon of energy Eγ under energy conservationE0 = Ef + Eγ :e0(E0) + A→ ef (Ef , ϑf ) + A + γ(Eγ , ϑγ) (1)The coincident detection of scattered electron ef(Ef , ϑf )and bremsstrahlung photon γ(Eγ , ϑγ) provides the moststringent tests for our understanding of the coupling be-tween a matter field and an electromagnetic field.Of particular theoretical interest is the case, when the en-tire kinetic energy of the incident electron is transferred tothe photon; the theoretical description of the resulting high-energy endpoint of the electron-nucleus bremsstrahlungspectrum is closely related with photoionization PI and ra-diative electron capture REC. This process is not accessiblein classical setups, where energetic electrons are scatteredoff high-Z target atoms at rest.However, using a setup in inverse kinematics, namelyhighly charged heavy projectiles from the ESR, like U 88+,scattering off quasi-free electrons, enables us to performcoincidence measurements at the high-energy endpoint, asthe scattered electron at rest in the moving frame appearsin the 0◦-cusp in the laboratory frame. Here the electroncan be understood alternatively as radiatively captured intothe continuum of the projectile (RECC).In order to measure triple differential cross-sectionsd3σ/dEe/dΩe/dΩγ of the RECC process a beam of U 88+was injected into the ESR at 90MeV/u intersecting a super-sonic N2 gas target. Cusp-electrons emitted from the gastarget into the forward direction ϑf =0◦ at velocities closeto the projectile velocity where detected with the ESRelectron spectrometer. The spectrometer consists of two60◦-dipole magnets for momentum analysis and an iron-free quadrupol-triplett in between the dipols to enable tele-scopic imaging onto a position sensitve MCP-delayline-detector (cf. last annual report [1]). To measure the X-rays five standard Ge-detectors where used at angels ϑγ =+35◦, +90◦, +150◦, −90◦, and −145◦ around the inter-action point. Particle detectors in the ESR dipole magnetswhere used to detect capture and ionization events.Using this setup we were able to measure for the RECCprocess the electron energy distribution for five differentphoton emission angles, and accordingly the photon angu-40 50 60 70 80 90 10001234560.5 0.1 0 0.1 0.5 1 2 3 4 5 6 7 8electron energy in laboratory frame Ee keVd3ΣdE ededΓbarnkeVsr2electron energy in projectile frame Ee' keVpreliminaryFigure 1: Electron energy distribution for forward emittedelectrons in coincidence with a photon emitted at ϑγ =+90◦.lar distribution of the electron-nucleus bremsstrahlung atthe high-energy endpoint.Fig. 1 shows examples of preliminary results for theelectron energy distributions. The cross section is givendifferentially in electron energy dEe, electron emission an-gle dΩe and the photon emission angle dΩγ while beingintegrated over the energy of the coincident photon energyEγ . The distribution is peaked above the electron energy ofE0 = 49.6keV corresponding to E ′f = 0 projectile frameenergy. The strong asymmetry of the cusp shows that elec-trons are in the projectile frame predominately emitted intothe forward direction. The spectra will be compared withstate-of-the-art theories such as [2].P.-M. H. greatfully acknowledges support by HGS-HIRe.References[1] P.-M. Hillenbrand, Commissioning of the electron spectrom-eter at the ESR, GSI Scientific Report 2011[2] D.H. Jakubassa-Amundsen, Radiative ionization: The linkbetween radiative electron capture and bremsstrahlung, Ra-diation Physics Research Progress, 2008, pp.155-191GSI SCIENTIFIC REPORT 2012 PNI-INHOUSE-EXP-01369

Electron spectroscopy at the high-energy endpoint of electron-nucleus  bremsstrahlung

http://repository.gsi.de/record/52262/files/PNI-INHOUSE-EXP-01.pdf

Electron spectroscopy at the high-energy endpoint of electron-nucleus bremsstrahlung

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