G Bochek, V Kulibaba, N Maslov, V Ovchinnik, B Shramenko
The experimental investigation o f radiation energy losses o f ultra relativistic electrons in aligned crystals of various atomic number are o f great interest for several reason. On the one hand, they helps in searching optimal conditions for у-quantum beam generation and in achieving maximum convertion factor o f electron energy to that o f у-radiation. On the other hand, being compared with calculation performed according to various theoretical models, they allows one to choose the model
more » ... hoose the model that describes an electron interaction with ordered crystal structure most completely. Such experimental data have been obtained at ICharkov 2GeV linear in NSC KhlPT. The experimental data measured for the radiation angles near the angle 9^ = me' / are most interesting. We present below the results o f our measurements o f electron energy radiation losses for radiation angles interval 0.5 to 5 Measurements were done for 0.52 and 1.18 mm tungsten single crystals at electron energy 0.9 and 1.2 GeV, the electron beam being directed along axes <111> and <100> respectively and for 0.8 mm germanium and 15 mm silicon crystals at electron energy 1.2 GeV. On all cases the total radiation losses were measurement with a quantometer and a technique described in ref.[l]. Besides, the total radiation losses in 1.18 mm tungsten and 15 mm silicon crystals were found by means o f integration the spectral distributions of у-radiation over energy, as it is described in ref. [2]. The total radiation losses obtained by means o f both technique are in a satisfactory agreement with each other. The у-radiation spectrum from the tungsten crystals of various thickness are interesting in itself A new measurement technique [3] permitting one to exclude the spectra distortion through the multiplicity o f у-quantum creation by a single electron made it possible:-to obtain information about "true" radiation spectrum from heavy crystal o f large thickness, up to unit o f radiation length;-to make clear the effect of the shape o f radiation spectrum on the total radiation losses. The radiation spectrum from the tungsten crystals of various thickness averaged over measured experimental points, are presented in fig. 1 and 2. It is seen from fig.l, that the spectrum curve for the tungsten crystals o f 1.18 and 3.2 mm thickness have practically coinciding maximum at the у-quanta energy = 22 MeV. They are shifted to the hard part o f the spectrum in comparison with intensity maximum in silicon crystal, placed at = 15 MeV [8]. But these spectra considerably differ from each other in intensity in the whole interval o f у-quanta energy (ю). The most visible decrease in intensity is observed in the hard part of spectrum, beginning from co>20 MeV (see fig.2). This is likely to be caused by decrease in a number o f у-quanta because of pair creation. The intensity decrease in the hard part o f spectra together with у-quanta beam space distribution broadening which is due to the effect of electron multiple scattering getting larger, leads to the fall In the total radiation losses in a fixed solid angle with the growth o f the crystal thickness. The measurements we have performed show that for sharply directed radiation (the collimation angle Oc=O.510^) the total radiation losses in the tungsten crystal o f 3.2 mm thickness