Channeling of swift positrons in silicon crystal

Abstract

The channeling of (16--28)McV electrons and positrons scat tercd into the angular range from 0.9 to 1.0 degrees with respect to the beam direction and in the forward bremsstrahlung yield after the transmission through a Si single crysta l was previously observed (~). The effect of Si crys ta l or icntat ion on the brenlsstrahlmlg intensi ty yield generated by 1 GcV clcctrons and positrons was also studied (2). The angular parameters of the measured distr ibutions were compared with the L indhard theoretical estimations (a) and a qu,xlitative agreement was observed. On the other hand the numerous measurements on the heavy-par t ic le channeling and the s tudy of the positron motion in the crys ta l la t t ice (4..~) dis t inct ly slow the good fitness of the computer simulati(m method for the description of the measured distr ibutions. However, the classical t rea tment of the inelastic collisions of the channeled par t ic le with the la t t ice atoms is hampered, and t~he quantum mechanical approach is necessary for tim brcmsstrahlung effect c~flculations. Therefore, the measurement of elast ic-scattering yield of the relat ivist ic p~u'ticles is of special interest for the comparison with the classical theory of the channeling phenomenon. In the present investigation the effect of < 11 l ) Si-crystal orientation on the multiplescat ter ing yield of positrons of energy 40, 80 and 160 MeV wa.s measured. The experimeI~t'tl results arc considered both on the basis of the continuum approximat ion and on the da ta of the binary-collision c~dculations according to the previously described model for the simulation of the t rajectories of the l ight charged part icles (4). The positron beam was produced in the 6 mm thick copper target i r rad ia ted by the collimated bremsstrahlung beam with the maximum energy up to 800 MeV, generated i n , t h e internal target of the synchrotron of the Tomsk Polytechnical Ins t i tu te (~).