Radiation of channeled 800 MeV electrons in diamond crystals

Volume 70A, number 5,6

PHYSICS LETTERS

2 April 1979

RADIATION OF CHANNELED 800 MeV ELECTRONS IN DIAMOND CRYSTALS B.N. KALININ, V.V. KAPLIN, A.P. POTALITSIN and S.A. VOROBIEV Institute for Nuclear Physics, Tomsk Polytechnical Institute, Tomsk 634050, USSR Received 6 November 1978

Measured data on ‘y-ray emission for the low-energy region of the bremsstrahlung spectra produced by 800 MeV electrons in diamond crystals are presented. The obtained spectral and orientational characteristics of the ~-ray yield indicate that the low-energy radiation is associated with the channeling of electrons.

In the present work the y-ray yield in the lowenergy region of the bremsstrahlung spectra of 800 MeV electrons have been observed up to the minimum energy w = 0.02 E = 16 MeV, in order to look the characteristics 0associated with channeling of for relativistic electrons in single crystals. Experimental measurements were performed with the internal beam of

the Tomsk synchrotron on a diamond single crystal with a thickness of 0.016 radiation units (about 2 mm). The divergence of the electron beam was less than 5 X i~—~ rad and the energy spread was not poorer than 0.5%. The collimated 7-ray beam produced in a diamond crystal with atarget divergence of 3 rad, was ontodirected, the converter of a magne0.6 X iO— tic 7-ray spectrometer and monitored with the use of a Gauss quantameter. The energy resolution of the ‘yray spectrometer varied from 7% at w = 20 MeV to 3% at w = 120 MeV. The diamond crystal was oriented to an accuracy of 5 X l0—~rad with the help of a goniometer device. Themeasurements usually were carried out with the electron momentum along the (001) crystallographic plane and the tilting angle 0 was read from the (110) axis. Fig. 1 shows the measured 7-ray spectrum for 0 00 diamond orientation, which exhibits a large enhancement oflow-energy radiation at w<60 MeVascompared with completely “random” transmission of the electron beam relative both to the (110) axis and the (001) plane. The anomalous 7-ray emission can be explained as due to the effect of electron channeling, This effect is known to occur at angles of beam mci-

dence, relative to the crystallographic axis, 0 ~ 0L (4Ze2/dp 1/2 where Z is the atomic number, d is 1v) distance, Pi and v are the electron mothe interatomic 0L is Lindhard’s mentum and velocity, respectively, andof a channeled critical angle. The radiation frequency electron in spiral motion with relativistic longitudinal velocity will be v ~ 272v 1r~,where 7 is a relativistic factor, ris the spiral radius and u1 is the particle velocity transverse to the spiral axis. The spiral trajectories will be stable at aTF
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= 0 to the radiation yield of an electron beam in “random” transmission with respect to the <110) axis and the (001) plane of diamond.

447

Volume 70A, number 5,6

PHYSICS LETTERS

tion, P 0L may be given by the “transitional channeling” effect, under which the electrons are moving near the atomic planes successively rounding the atomic rows [5]. This channeling behaviour, when the electron trajectories oscillate with period r 2d~(v0)~1, where d~is the distance between the atomic rows, is transitional between the axial and planar effects. The contribution of coherent effects in such a type of radiation will determine the correspondence between the radiation under channeling and the coherent bremsstrahlung, which in common can describe the 7-ray emission from the crystal target. Fig. 2 shows the measured orientational dependence of 7-ray emission with energy for w = 30,40 and 50 MeV, which demonstrates that the channeling radiation dominates the coherent bremsstrahlung in the low-energy region. At higher energies the coherent maxima grow more appreciable and at w = 50 MeV the orientational dependence has a form, which is typical for coherent bremsstrahiung at w > 0.1E 0 [3,4].

2 April 1979 ____________-

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In conclusion, we should note that recently the additional low-frequency radiation has been observed in the scattering of 28 MeV electrons in silicon [6], which was attributed to channeling radiation [7]. The angular characteristics of optical radiation of 2.0 MeV electrons under channeling were also observed and discussed [8]. The present work gives the first results for high-energy electrons and the spectra! and orientational characteristics of channeling radiation are clearly demonstrated. Refrrences [1] A. Ya. Babuclaev, V.V. Kaplin and S.A. Vorobiev, Phys. Lett. 45A (1973) 71. [21V.V. Kaplin and S.A. Vorobiev, Fiz. Tverd. Tela 20 (1978) [3] GD. Palazzi, Rev. Mod. Phys. 40(1968)611. [4] U. Timm, Fortschr. Phys. 17 (1969) 765. [5] V.V. Kaplin, D.E. Popov and S.A. Vorobiev, Phys. Stat. Sol. 76b (1975) 779. [6] R.L. Walker, B.L. Berman and S.D. Bloom, Phys. Rev. All [7] R.W.Terhune and R.H. Pantell Appl. Phys. Lett. 30(1977)

265. [8] A.A. Vorobiev, V.V. Kaplin and S.A. Vorobiev, Nuci. Instrum. Meth. 127 (1975) 265.