Sokolov-Ternov effect

Sokolov-Ternov effect

The Sokolov-Ternov effect is the effect of self-polarization of relativistic electrons or positrons moving at high energy in a magnetic field. The self-polarization occurs through the emission of spin-flip synchrotron radiation. The effect was predicted by Igor Ternov and rigorously justified by him and Arsenij Sokolov using exact solutions to the Dirac equation [cite journal|author=A. A. Sokolov and I. M. Ternov|title=Polarization and Spin Effects in the Theory of Synchrotron Radiation|journal=Dokl. Akad. Nauk SSSR|volume=153|pages=1053|year=1963|url= [in Russian] .] [cite journal|author=A. A. Sokolov and I. M. Ternov|title=On Polarization and Spin Effects in Synchrotron Radiation Theory|journal=Sov. Phys. Dokl.|volume=8|pages=1203|year=1964|url= ] .

Theory

Electron in a magnetic field can have spin oriented in the same ("spin up") or in the opposite ("spin down") direction with respect to the direction of the magnetic field (which is assumed to be oriented "up"). The "spin down" state has a lower energy than "spin up" state. The polarization arises due to the fact that the rate of transition through emission of synchrotron radiation to the "spin down" state is slightly greater than the probability of transition to the "spin up" state. As a result, an initially unpolarized beam of high-energy electrons circulating in a storage ring after sufficiently long time will have spins oriented in the direction opposite to the magnetic field. Saturation is not complete and is explicitly described by the formulacite book|last=A. A. Sokolov and I. M. Ternov|publisher=American Institute of Physics Translation Series. Edited by C. W. Kilmister|location=New York|title=Radiation from Relativistic Electrons|year=1986|isbn=0883185075 Section 21.3 for the theory and section 27.2 for experimental verifications of the Sokolov-Ternov effect.]
xi(t)=ABigl(1-e^{-t/ au}Bigr)
where A=8sqrt{3}/15approx 0.924 is the limiting degree of polarization (92,4%) and au is the relaxation time,
au=8{hbar}^2}over {5sqrt{3}mc{e}^2Bigl(mc^2}over {EBigr)^2Bigl({H_0over H}Bigr)^3
Here m and e are the mass and charge of the electron, c is the speed of light, H_0approx 4.41 imes 10^{13} G is the Schwinger field, H is the magnetic field, and E is the electron energy.

The limiting degree of polarization A is less than one due to the existence of spin-orbital energy exchange which allows for transitions to the "spin up" state (with probability 25.25 times less than to the "spin down" state).

Typical relaxation time is on the order of minutes and hours. Thus producing a highly polarized beam requires a long enough time and the use of storage rings.

The self-polarization effect for positrons is similar, with the only difference that positrons will tend to have spins oriented in the direction parallel to the direction of the magnetic field [cite book|last=J. Kessler|publisher=Springer|location=Berlin|title=Polarized Electrons. 2nd edition|year=1985 Section 6.2.] .

Experimental observation

Sokolov-Ternov effect was experimentally observed in the USSR, France, Germany, USA, Japan, and Switzerland in storage rings with electrons of energy 1-50 GeV. [cite book|last=V. A. Bordovitsyn (editor)|publisher=World Scientific|location=Singapore|title=Synchrotron Radiation Theory and Its Development: in Memory of I. M. Ternov|year=1999|isbn=9810231563|url=http://www.worldscibooks.com/physics/3492.html]

*1971 — Budker Institute of Nuclear Physics (first observation), with the use of 625 MeV storage ring VEPP-2.
*1971 — Orsay (France), with the use of 536 MeV АСО storage ring.
*1975 — Stanford (USA), with the use of 2.4 GeV SPEAR storage ring.
*1980 — DESY, Hamburg (Germany), with the use of 15.2 GeV PETRA.

Applications

The effect of radiative polarization provides a unique capability for creating polarized beams of high-energy electrons and positrons that can be used for various experiments.

The effect also gives strong evidence for experimental observation of the Unruh and Hawking radiations. Under experimentally achievable conditions for gravitational systems these radiations are too small to be observed. Recent work [Emil T. Akhmedov and Douglas Singleton. [http://arxiv.org/abs/0705.2525v3 On the physical meaning of the Unruh effect] .] shows that if one takes an accelerated observer to be an electron circularly orbiting in a constant external magnetic field, then the Sokolov-Ternov effect coincides with the Unruh effect, which is closely connected to the Hawking radiation.

Patent

* Sokolov A. A. and Ternov I. M. (1973): Award N 131 of 7 August 1973 with priority of 26 June 1963, Byull. Otkr. i Izobr., vol. 47.

References

ee also

*Unruh effect
*Hawking radiation


Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • Sokolov — ( ru. Соколов, masculine) or Sokolova ( ru. Соколова, feminine) is one of the most common Russian last names. It is derived from the Russian word ru. сокол ( sokol , falcon). It may refer to the following:Places*Sokolov (Sokolov District), a city …   Wikipedia

  • Arsenij Sokolov — Infobox Scientist name = Arsenij Sokolov image width = 140px caption = birth date = birth date|1910|3|19|df=y birth place = Russia, Novosibirsk death date = death date and age|1986|10|19|1910|3|19 death place = Russia, Moscow residence =… …   Wikipedia

  • Igor Ternov — Infobox Scientist name = Igor M. Ternov image width = 140px caption = birth date = birth date|1921|11|11|df=y birth place = Russia death date = death date and age|1996|4|12|1921|11|11 death place = Moscow, Russia residence = citizenship =… …   Wikipedia

  • Unruh effect — The Unruh effect (or sometimes Fulling–Davies–Unruh effect), was first described by Stephen Fulling in 1973, Paul Davies in 1975 and Bill Unruh in 1976.[1][2][3] It is the prediction that an accelerating observer will observe black body radiation …   Wikipedia

  • Électron — Traduction à relire Electron → …   Wikipédia en Français

  • Electron — For other uses, see Electron (disambiguation). Electron Experiments with a Crookes tube first demonstrated the particle nature of electrons. In this illustration, the profile of the cross shaped target is projected against the tube face at right… …   Wikipedia

  • Synchrotron radiation — This article concerns the physical phenomenon of synchrotron radiation. For details on the production of this radiation and applications in laboratories, see Synchrotron light source. The electromagnetic radiation emitted when charged particles… …   Wikipedia

  • Storage ring — The 216 m circumference storage ring dominates this image of the interior of the Australian Synchrotron facility. In the middle of the storage ring is the booster ring and linac A storage ring is a type of circular particle accelerator in… …   Wikipedia

  • Hadron Elektron Ring Anlage — HERA ( Hadron Elektron Ringanlage , or Hadron Electron Ring Accelerator) was a particle accelerator at DESY in Hamburg. Its operation started in 1992. At HERA, electrons or positrons were collided with protons at a center of mass energy of 318… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”