The transmission of synchrotron radiation through magnetized iron at energies above the A>absorption edge shows relative differences for right and left circular polarization of several times 10 ~4. The observed spin dependence of the near-edge photoabsorption is proportional to the difference of the spin densities of the unoccupied bands. In the extended absorption region up to 200 eV above the Fermi level a small spin-dependent absorption is observed and thus is expected to give information on the magnetic neighborhood of the absorbing atom.PACS numbers: 75.50. Bb, 75.10.Lp, 78.70.Dm For a better understanding of the remaining problems of ferromagnetism, especially for a clarification of the controversy between the "localized"-and "itinerant"-electron models, 1,2 further experiments are needed to determine the spin-density distribution within the bands near the Fermi level. Besides studies of spin polarization of the occupied states with spin-resolved photoemission spectroscopy, 3 it is of equal importance to investigate the unoccupied ones, which play an essential role for spin fluctuations and excitations. The first steps to address this interesting problem were taken by spin-polarized inverse photoelectron spectroscopy. 4,5 However, because of the small range of low-energy electrons this method is sensitive only to surface layers, whose magnetic properties may differ from those of the bulk. 6 Furthermore the method used is restricted by the limited energy range in which low-energy photons can be detected efficiently by Geiger-Muller counters. The magneto-optic Kerr effect, which is sensitive to the electron spin polarization of states both below and above the Fermi level, is difficult to interpret. 7 Recently we have shown, 8 ' 9 using 9.17-keV circularly polarized x rays emitted after internal conversion in the decay of excited oriented nuclear states, that the photoabsorption cross section of iron contains at these relatively high energies a small spindependent contribution of (1.7 ±0.4) x 10 ~3. Highenergy storage rings are intense, energy-tunable sources of circularly polarized synchrotron radiation (CPSR) in the kiloelectronvolt energy range observable at welldefined small angles above and below the plane of the electron orbits. Thus it seemed to be feasible to measure the spin dependence of photoabsorption above the K edge of 3d ferromagnets. Similarly one may study spindependent L-and A/-edge absorption in magnetic materials containing 4/ and 5/ elements, respectively. Recently an upper limit of 2xl0~3 was observed for the spin-dependent part of the Gd Z,3-edge absorption in a Fe82Gdi8 alloy. 10 In the course of this work, we have observed 11 a remarkably large spin dependence of the photoabsorption in Gd metal at the L 3 and Li edges of 10 ~2 with opposite sign. Here we present the first observation of spin-dependent absorption in the AT-edge region of iron using CPSR from the storage ring DORIS at the Deutsches Elektron-Synchrotron DESY. Our method is discussed as a new technique to determine spin...

Positron lines were observed in heavy ion-atom collisions at bombarding energies close to the Coulomb barrier in subcritical systems with the sum of the atomic numbers of the colliding nuclei Zu=ZI +Z2 being smaller than Z,= 172. Each collision system, studied, 2~176 238U+ 181Ta(Z,=165), and 238Au(Zu= 171), exhibits the emission of two positron lines with Z,-independent c.m. energies of ~ 258 keV and ~340 keV, and with widths of about 30 keV, superimposed on continuous positron spectra from nuclear pair decay and pair emission induced by the time changing Coulomb field of the collision. The production cross section of the e + -lines rises with a high of Z,, (ocZ, ), which is comparable to the Z~~ for the collision induced power 22 positrons.

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Abstract:In fusion reactions of 58Ni beams with 54Fe and 58Ni target nuclei neutron deficient evaporation residues have been produced and separated from the beam in an electrostatic deflector with large acceptance. The recoil nuclei were implanted and detected in an array of 100 PIN photodiodes, where also their particle decays were recorded. The assignment of the 0.81 MeV proton line to the decay of 1~ could be experimentally proven by the observation, that it is followed by the 3.31 MeV alpha emission from 1~A proton decay from llYCs was not observed. The decay energies of a number of known c~ emitters have been measured with better precision.

The first evaluation of spin-dependent extended x-ray-absorption fine structure (SPEXAFS) is reported. The SPEXAFS at the Gd L edges for Gd metal and Gd3Fe50l2 are compared to the conventional EXAFS and discussed in terms of exchange scattering from magnetic neighbors. The SPEXAFS at the Gd L2 and L3 edges reflect the change of the photoelectron spin polarization. The Fourier transform of the SPEXAFS of the Gd3Fe50lz only shows the magnetic neighborhood, whereas the nonmagnetic oxygen neighbors remain invisible. SPEXAFS spectroscopy is expected to become a powerful tool in the determination of the magnetic short-range order.