fall-off time, P ~ (t) 10~20ns shows a speedy reduction, whereas P ~ (t) 10~60ns keeps a nearly fixed value. Fluctuation of the magnetic moment in the crystal is decreased by the time development of the magnetic relaxation. Takaya Mitsui SPring-8 / JAERI E-mail: taka@sp8sun.spring8.or.jp References [1] Yu.V. Shvyd’ko, Hyp. Interact. 90 (1994) 287. [2] T. Mitsui et al., Jpn. J. Appl. Phys. 36 (1997) 6525. [3] T. Mitsui et al., Hyp. Interact. (c) 3 (1998) 429. [4] S. Kikuta, Hyp. Interact. 90 (1994) 335. TIME AND ENERGY SPECTRA OF INTERNAL CONVERSION ELECTRONS FROM 57 Fe FOIL Energy distribution and time spectra of internal conversion electrons from 57 Fe foil were measured at the BL09XU beamline. The emission signal of conversion electrons excited with incident X-ray photons was discriminated by electron energy analysis and intense prompt noise was excluded in the signal processing. The apparatus consists of an electrostatic electron energy analyzer and a sample manipulator contained in an ultrahigh vacuum chamber. The analyzer we developed was a planar electrostatic quadrupole type assembled on a 203 mm Conflat-type flange. The electrons incident through an entrance slit of the analyzer were deflected at an angle of 90 inside the hyperbolic electrostatic field. The acceptance angle and the energy resolution were 0.04 π and 4%, respectively. An avalanche photodiode (APD) detector was attached at the exit of the analyzer. The APD detector proved high detection efficiency for high- energy electrons as well as excellent time response (< 1 ns) and noise characteristics (< 0.01 cps). The photons from an in-vacuum undulator are monochromatized to a band-width of 2 meV by a high-resolution nested channel-cut monochromator. The counting rate of APD detector for the prompt emission of photoelectrons was 1.4 x 10 6 cps. The energy spectrum of the electrons excited with a 14.413 keV X-ray is shown in Figure 1. To suppress the enormous counting rate of prompt emission of photoelectrons, the output pulse of the APD detector is discriminated in the time-domain between 10 and 190 ns after the incidence of synchrotron radiation. The peaks of K- and L-shell conversion electrons and KLL Auger electrons are clearly observed in the figure. The maximum counting rate at the peak energy of K-shell conversion electrons was 0.51 cps. The tail in the low energy side is due to the cascade inelastic scattering of electrons inside the sample. The energy resolution of 4% corresponds to the escape depth of 20 nm. 26 Fig.1: Energy distribution of electron emission from 57 Fe foil within a time-interval between 10 and 190 ns after incidence of primary photons. The time spectrum of the K-shell conversion electrons is shown in Figure 2. The principal structure of the time spectrum is an exponential decay with the time constant of 131 ± 17 ns, which coincides with the decay time of isolated 57 Fe nuclei, 141 ns. Compared with the time spectrum of the nuclear resonant photon emission for the same sample, neither the speed-up of decay process nor quantum beat structure is observed. The present results illustrate the incoherent nature and surface layer sensitivity of conversion electron emission. Tatsuo Okano a , Taizo Kawauchi a and Zhang Xiao-Wei b (a) The University of Tokyo (b) KEK E-mail: okano@iis.u-tokyo.ac.jp X-RAY PARAMETRIC DOWN CONVERSION AT THE BREWSTER ANGLE X-ray parametric down conversion originating from the property of free electrons is one of the nonlinear phenomena in the X-ray region. The phenomenon that one X-ray photon is converted to two photons was observed by Eisenberger et al. using an X-ray tube [1] and by Yoda et al. using synchrotron radiation [2]. The polarization dependence in X-ray parametric down conversion is different not only from that in Thomson scattering but also from that in optical parametric conversion. In the latter case, the spatial symmetry of a nonlinear optical medium restricts the form of the nonlinear optical susceptibility. The X-ray parametric down conversion was observed in such a geometry that the π -polarized X-rays are incident on the crystal at the Brewster angle where Thomson scattering is prohibited. The experiment was performed at the beamline BL09XU . The linear polarized X-rays in the horizontal plane can be obtained by the in- vacuum horizontal undulator. The storage ring was operated in multi-bunch mode with 2 nsec pulse intervals and its typical current was 17 mA. X-rays from a Si (111) inclined double-crystal monochromator were incident on a diamond single crystal as shown in Figure 1. T.Okano, T.Kawauchi, X.-W. Zhang, K.Fukutani, Y.Yoda, U. Teerapongpipat and S.Kikuta, Submitted to Japan J. Appl. Phys. 27 Fig. 2.: Time spectrum of K-shell conversion electrons from 57 Fe foil. Accumulation time of the spectrum was 7.8 hours. Fig.1: Experimental setup. Two APD detectors were arranged at scattering angles of nearly 90 degrees.
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