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2.14 Spin-Flip Transitions in Radiative Electron Capture Into Bare Uranium

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2.14 Spin-Flip Transitions in Radiative Electron Capture Into Bare Uranium DEPARTMENT OF NUCLEAR SPECTROSCOPY AND TECHNIQUE 51 The ANKE-GEANT geometry package describes GEANT original output files, prepared by calling precisely a full spectrometer: magnets, vacuum corresponding procedures [1]. One event consists of chambers, target chambers, detector systems etc. The several tracks and more than one particle can appear in real set-up is divided into parts easily converted into it. Typical parameters of the particle track, like time of shapes supplied by GEANT. Preparation of flight, energy loss and path length for each detector, description of the ANKE geometry for the Monte are stored. These data can be written in the same Carlo code was a time consuming task, which has format as measured data. So, the same data analysis started from measurements of dimensions and program may be used for experimental and simulated positions of all ANKE elements. Necessary data are data. already placed in the ANKE WWW page and in a Simple response functions for scintillators are close future will be available from the database. implemented in the ANKE-GEANT program and Measured dimensions and positions of all elements of placed in the ntuple-like file called the ANKE set-up are then used to calculate shape anke_geant_output.ntuple. parameters and positions of volumes according to the Monte Carlo simulations are very useful to GEANT convention. For the moment these determine a detector acceptance, estimate background, conversions are done in the main part of the ANKE- understand measured particle spectra. These GEANT program (written in FORTRAN). calculations are also necessary for identification of All physical phenomena (pair production, particles and calculations of their energy losses. The Compton scattering, photoelectric effect, Rayleigh Monte Carlo simulations are the only method to scattering, bremsstrahlung, hadronic process, reconstruct the momenta of ejectiles, from measured annihilation, 8-rays, muon nuclear interaction, hits in MWPC's for the two body calibration reactions. photofission, decay in flight, energy loss, multiple Calculated and measured parameters are used to verify scattering, Cerenkov photon generation, Cerenkov positions of set-up elements, or even to find correct light absorption, synchrotron radiation generation, values (e.g. by comparing the simulated and different energy fluctuation models) can be switched experimental hit distributions in MWPC's). on or off by the user. The user must choose values of parameters controlling these processes. [1 ] GEANT3 Manual, CERN Program Library Long For the description of the magnetic field in the Writeup W 5013 ( October 1994 ) space occupied by the ANKE facility the measured [2] MAFIA, The MAFIA Collaboration field maps are used in combination with three [3] S.Barsov et al., "Dipole Field Characterisation by dimensional field calculations made with the MAFIA Floating Wire and Field Map Ray Tracing", Proc. code [2]. The MAFIA calculations are checked by 16th Int. Conf. on Magnetic Technology, Ponte comparison with the floating wire measurements [3]. Vedra Beach (USA), Sept.26 - Oct.2. 1999 Full information about events can be obtained either from special files described in manuals or from PL0001491 2.14 Spin-Flip Transitions in Radiative Electron Capture into Bare uranium Ions by T.Ludziejewski, Th.StohIkerU), H.F.Beyer2), F.Bosch2), J.Eichler3), B.Franzke2), S.Hagmann4), A.Kramer1>2), C.Kozhuharov2', J.Lekki6', D.Liesen2), P.H.Mokler2), Z.Stachura5', P.Swiat6', and A.Warczak6) Photoionization is one of the most important inclusion of terms beyond dipole in a multipole interaction processes between radiation and matter. expansion of the photon field, results in a break-down Recently, it has been demonstrated that photo- of symmetry around 90° of the REC angular ionization can best be studied via its time inverse distribution. Surprisingly, deviations from sin20 reaction - the radiative electron capture (REC) distribution, turned out to be rather unimportant at ion occurring in ion-atom collisions [1]. For REC into the energies up to 300 MeV/u and nuclear charges up to ^-states of bare non-relativistic ions, the complete Z=50 or 70 [3]. However, a significant cross section at cancellation between retardation effects and the forward angles has been predicted for REC into the K Lorentz transformation occurs, leading to the classical shell of bare uranium (Z=92) at the same collision sin2G term in the angular distribution. In particular, energy, and shown to be a unique signature of spin-flip photon emission at 0° is forbidden by angular transitions [2]. momentum conservation law, unless a magnetic spin- Here, we report the first experimental study of a flip transition accounts for the spin of the emitted complete photon angular distribution for radiative photon [2]. For very high-Z systems, relativistic effects electron capture into the K shell of a bare high-Z ion become important and require the exact theoretical (uranium, Z=92). Our measurement conducted at the treatment, both in terms of electron wave-functions internal gas-jet target of the ESR Storage Ring at GSI used and the interaction potential. In particular, the Darmstadt, encompasses laboratory observation angles 52 Annual Report 1999 from near 0° to 150°, permitting to identify spin-flip laboratory frame (dashed line). Obviously, the contributions. experimental data deviate considerably from symmetry around 90°. Most significantly, the experimental data follow the predictions of the complete relativistic treatment, in which the interaction of the electron magnetic moment with themagnetic field produced by the moving projectile gives rise to spin-flip transitions at observation angles close to 0° (shaded area in Fig. 1). This effect, predicted recently [2], has not been confirmed experimentally up to now. For example, for the case of XeM+-> Be collisions at 197 MeV/u [3], no relativistic effects were observed and the measured AT-REC angular distribution could be well reproduced by the nonrelativistic theory. It should also be mentioned that in the relativistic Sauter approximation [4], in which the matrix element of the photoelectric effect is treated in the lowest order of aZ (a is the fine-structure constans) spin-flip contributions at forward angles do not occur. Hence, the present results indicate that higher orders in ocZ (automatically 0 30 60 90 120 150 180 contained in the exact wave functions) are needed. observation angle 9 [deg] Fig. 1 Angular distribution of REC into the K shell of bare [1] Th.Stohlker et al., Phys. Rev. Lett. 79, 3270 uranium ions. (1997). [2] A.Ichihara, T.Shirai, and J.Eichler, Phys. Rev. In Fig.l, the measured differential cross sections 92+ A49, 1875(1994). for REC into the K shell of U are presented as a [3] R.Anholt et al., Phys. Rev. Lett. 53, 234 (1984). function of the laboratory observation angle (solid [4] F.Sauter, Ann. PhysiA: 9, 217 (1931); 11 454 triangles) and compared with predictions based on (1931). rigorously relativistic treatment [2]. As seen in the figure, good agreement is obtained between the IKF University of Frankfurt (Germany) experimental data and the calculations (solid line). In 2) order to elucidate the necessity of a complete GSI-Darmstadt (Germany) 3) HMI-Berlin (Germany) relativistic treatment for high-Z projectiles, the figure 4) 2 KSU-Manhatten (USA) also includes the sin 6 distribution following from a 5) IFJ Cracow (Poland) non-relativistic treatment, which incorporates the full 6) University of Cracow (Poland) retardation, as well as the Lorenz transformation to the 2.15 Studies with the C-30 Cyclotron by J.Wojtkowska PL0001492 Using the 21 MeV proton beam of our C-30 In collaboration with Military Technical University 172 cyclotron the radioactive isotope Lu (T1/2=6.7d) in Warsaw and the Institute of Electronic Technology was produced (via the reaction mYb(p,n)) in the and Materials in Warsaw the proton beam from the following compounds of Yb: Yb3Ga50i2, YbNiBC, cyclotron was used to study radiation induced YbVO4, YbNi2B2C, YbPO4 and Yb2Ti307. modifications of such crystals as active laser radiators In the decay of 172Lu to 172Yb, two cascades: 91- and materials for optical wafers. This collaboration is 1094 keV and 1094-79 keV, give the possibility of continued from 1997 and following crystals doped l72 with rare-earth elements and metals were irradiated using Lu as a PAC (perturbed angular correlation) 4+ probe for investigation of different physical properties by 21 MeV proton beam: YAG:Cr , YAG:Ce, l72 YAG:CeNd, LiNbO3, LiNb, SrGdGa3, Gd3Ga50i2) of ytterbium compounds. In particular the Lu PAC 4+ probe is applied to the studies of Yb atom charge SrLaGa3O7:Cr , GdGa3O2:Cr, LiNbO3:Cr, LiNbO3:Fe states in solids, paramagnetic fluctuations and and LiNbO3:Cu. quadrupole interaction in excited states. These studies The crystals were irradiated with the fluency from are carried at the Institute of Physics of Jagiellonian 1013 up to 1016 protons per cm2. After crystal University in Cracow and the results were published irradiation, their optical properties were observed by [1-2]. measuring transmission, luminescence and thermo-.
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