1 / 15

Прямое наблюдение эффекта Бормана при дифракции нейтронов по Лауэ в кристаллах кремния

Прямое наблюдение эффекта Бормана при дифракции нейтронов по Лауэ в кристаллах кремния. Е.О.Вежлев 1,2 , В . В . Воронин 1,2 , И . А . Кузнецов 1 , С . Ю . Семенихин 1 , В . В . Федоров 1,2. 1 Петербургский институт ядерной физики

deidra
Download Presentation

Прямое наблюдение эффекта Бормана при дифракции нейтронов по Лауэ в кристаллах кремния

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Прямое наблюдение эффекта Бормана при дифракции нейтронов по Лауэ в кристаллах кремния Е.О.Вежлев1,2,В.В. Воронин1,2, И.А. Кузнецов1, С.Ю. Семенихин1, В.В. Федоров1,2 1Петербургский институт ядерной физики 2Санкт-Петербургский государственный политехнический университет

  2. Outline • Motivation • “Kato” theory of diffraction for deformed (bent) crystal • Influence of external force on diffracting neutrons • Two-crystal scheme introduction • Borrmann effect • Experimental observation of theory effectiveness for proposed scheme • mi / mG experiment with neutron • Summary

  3. For Laue diffraction with Bragg angles close to the right one there is a significant diffraction enhancment factor of an external affect on the neutron*: This factor can be used for observation of small external forces affecting the diffracting neutrons But, we must be sure that all of the dynamical diffraction predictions work well in thin (up to the 220 mm) crystals Motivation *V.V. Fedorov et.al. JETP Lett. 85, 82 (2007)

  4. z k g y (hkl) B kg Laue neutron diffraction in weakly deformed crystal (1) Neutron difraction in weakly deformed crystal can be described by imposing “Kato forces”*: Deviation from exact Bragg condition “Kato trajectories” are determined by the equation: (2) 2Fg V/d (1) or (2) *N.Kato , J. Phys. Soc. Japan (1963) 19, 971

  5. Influence of an external force Parameter of deviation from exact Bragg condition: Deformation changes the reciprocal lattice vector External force changes the incident neutron wave vector The “Kato force” for the neutron in this case: In fact, Fext||g is equivalent to the gradient of interplanar distances with the value Fext/2En

  6. Force affecting the neutron z k g Fn||Z y B kg Influence of an external force Neutron trajectory equation (Laue diffraction case): Equation for freely flighting neutron: We obtain a gain factor for the diffracting neutron For silicon(220) planes

  7. Two-crystal scheme of the experiment External force shifts the spot of the neutron beam at the exit surface: Due to well known Borrman effect* amplitudes will be different for two Bloch waves ψ(1) and ψ(2). In fact, we got different values of absorption for this two types of waves: Zero-harmonic of absroption Where g-harmonic of absorption *H. Rauch, D. Petrachek, in Neutron Diffraction (Springer, Berlin, 1978) 303-351

  8. Two-crystal scheme of the experiment In case of strong Borrmann effect (strong absorbing crystal): So, only one Bloch wave comes to the exit surface of the crystal. The resolution for this setup is: For (220) plane of Silicon:

  9. One-crystal scheme Theoretical prediction wtihout taking Borrmann effect into account Two-crystal scheme Experimental observation of Laue diffraction in the large silicon crystal (L=220 mm) Effective crystal length can reach few meters for 220 mm silicon crystal 220 silicon plane intensity reflex

  10. Ratio varies from 3/2 to 1/2 Experimental observation of Laue diffraction in the large silicon crystal (L=220 mm) The intensities ratio for one- and two-crystal schemes of the setup • Ratio depends on two-crystal scheme setup geometry • Experimental results coincide with the theory

  11. FG Fr Earth Sun neutron Possible applications. mi/mG experiment with neutron (I) FG= Fr for the Earth FG Frfor the neutron Possible arrearence of the non zero force:

  12. gc gc Possible applications. mi/mG experiment with neutron (II) FG Fr 0:00 Fm gc Fm changes its sign in the laboratory coordinate system 12:00 Fm gc Daily oscillations of the Fm value The possible sensitivity of the setup: *Present accuracy 2∙10-4 (Schmiedmayer, 1989)

  13. Possible applications. mi/mG experiment with neutron (III) Large silicon crystal (220 mm) Layout of the experimental setup (Already mounted on the beamline of WWR-M)

  14. Silicon (220) WWR-M reactor (PNPI, Gatchina)

  15. Summary • Two-crystal scheme of the Laue diffraction with bragg angles close to the right one is avery sensitive experimental instrument (resolution to the external force reaches 10-12eV/cm) • The uncertaintity of measuring inertial to gravitational mass ratio for the neutron (in fact, direct test of PoE) can reach magnitude ~10-5 • It’s possible the new instrument for measuring en

More Related