Double-layer targets for forming the beams of the high-energy photons on the electron accelerator of M-30 microtron


Purpose. The bremsstrahlung received at electron accelerators is widely used to study the characteristics of photonuclear reactions and to solve a wide spectrum (series) of applied problems. Basically the output of bremsstrahlung depends on the electron energy, the material of the target converter (Ta) and its effective thickness. The optimum thickness of the converter (when the output of the bremsstrahlung is at its maximum) is significantly less than the electron path in it. This is the reason for the presence of high-energy electrons in bremsstrahlung. Therefore, there is a need to clean the bremsstrahlung beams from residual electrons. The aim of the work is to experimentally determine the optimal parameters (thicknesses) of double-layer targets for obtaining separated bremsstrahlung beams for an energy range of 6.5 ÷ 17.75 MeV in electron accelerator M-30 microtron.
Methods. Experimental studies of the relative absorption coefficient of electrons in the investigated materials (C (reactor graphite), Al, Ta) were carried out on the M-30 microtron using the transmission method. The measurements of the outputs of the electrons from the accelerator and the residuals that have passed through the layer of absorbing material were carried out using a pass-through chamber and a Faraday cup, respectively. Studies of the absorption of high-energy photons by single-layer targets (C (20 mm), Al (20 mm)) using activation detectors have been carried out.
Results. The electron absorption coefficients in single- (C (7 ÷ 46 mm), Al (8 ÷ 48 mm), Ta (0.1 ÷ 1 mm)) and in double-layer targets (Ta (1 mm) + C (7 ÷ 39 mm) and Ta (1 mm) + Al (8 ÷ 40 mm)) were measured for the electron energy 6.5 ÷ 17.75 MeV. The values of the total electron absorption thickness for C, Al, and Ta are in good agreement with the calculated values of the practical electron path (database «ESTAR») for the indicated energy range. The experimentally established values of the thicknesses of materials (C and Al at a thickness of Ta – 1 mm) of doublelayer targets, which ensure the complete absorption of electrons for the indicated energy range. The absorption of high-energy photons by single-layer targets (C (20 mm), Al (20 mm)) for bremsstrahlung energy of 17.5 MeV was evaluated.
Conclusions. The optimal parameters (thicknesses) of double-layer targets (Ta (1mm) + C (20 mm) and Ta (1 mm) + Al (20 mm)) or (Ta (1mm) + C (39 mm) and Ta (1 mm) + Al (32 mm)) were established experimentally to form the separated bremsstrahlung beams in the electron accelerator – M-30 microtron for energy region 6.5 ÷ 17.75 MeV. The use of two-layer targets allows us to carry out procedures to form of high-energy photon beams with the parameters necessary for performing specific experimental studies on electronic accelerators, which will increase the accuracy and reliability of the results

Keywords: microtron, bremsstrahlung, residual electrons, electron absorption, double-layer targets