Twenty Years of Microtron Laboratory Activities at CTU in Prague

I for medical diagnostic purposes), et cetera. Participation of the microtron laboratory in the education of students of the faculty in various fields of applied dosimetry and other microtron applications is also discussed

Some Aspects of Profiling Electron Fields for Irradiation by Scattering on Foils

) for 1 mA of total beam current as functions of the distance from the beam exit window and of the thickness of the Al scattering foils

The System for Control and Stabilization of the Beam Position in the Microtron MT-25 in Prague

A method of control the beam position at crucial points of the transport system and for the stabilization of its output position has been proposed and preliminary tested. The method is based on secondary electron emission from a thin metallic wire probe induced by electrons from the 25 MeV microtron. It was demonstrated, that magnetic field of the order of 0.2 T and parallel to the wire probe in front of the orifice of the extraction channel in the acceleration space, does not prevent the functioning of the method. A strong parasitic effect of secondary electron emission from the material of the channel and its support construction was found, leading to the inversion of the electron current polarity from the wire. This effect can be to great extent eliminated by negative electric potential bias relative to the channel. At the electron output current of 1 mA the secondary emission current from the wire probe of 0.3 mm diameter is of the order of several nA. Two electromechanical systems were designed for the removal of the probes from the beam path, to avoid the deterioration of the electron beam quality by scattering. Electronic schemes used for remote measurement of small probe currents, suppressing the influence of strong electromagnetic noise, are described. For stabilization of the output beam position two wire probes situated in air close to the Al output window were used. These probes having been placed at the periphery of the beam did not deteriorate the beam quality. The difference of their emission currents was used as an error signal to control the magnetic field of the last dipole, which kept the beam in the center of the output window.

Faraday Cup for Electron Flux Measurements on the Microtron MT 25

The basic criteria for constructing of an evacuated Faraday cup for precise measurement of 5 to 25 MeV electron beam currents in air from a microtron are established. The Faraday cup, built in the microtron laboratory of the Faculty of Nuclear Sciences and Physical Engineering of CTU Prague, is described together with the electronic chain and its incorporation in the measuring line on the beam. Measures to reduce the backward escape of electrons are explained. The range of currents is from 10–5 to 10–10 A. The diameter of the Al entry window of the Faraday cup is 1.8 cm, and its area is 2.54 cm2. The thickness of the entry window is 0.1 mm

Filling and Recycling Apparatus of a Cyclotron Target with Enriched Krypton for Production of Radiopharmaceuticals

An apparatus for multiple filling of a cyclotron target with enriched Kr gas is described. The system is based on recycling pressurized gas by cryogenic pumping between the target tube and storage containers. The design and construction makes use of previous experience in the construction and operation of two analogue apparatuses for Xe124 high pressure gas targets, but major modifications have been incorporated, evoked by the different physical properties of Kr, by the character of the nuclear reaction, and by the demand for automation from the side of the end user

Irradiation of luminescence dosimeters in pulsed mixed radiation fields

UHDpulse - Metrology for Advanced Radiotherapy using beams with Ultra-High Pulse Dose Rates is a European project aimed at developing novel dosimetry standards, as well as improving existing ones, for FLASH radiotherapy, very high energy electrons radiotherapy, and laser-driven medical accelerators. Within the scope of this project, Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) detectors are used to measure stray radiation fields. Experiments performed with conventional pulsed particle-beams allow to characterize the dosimeters in known and controllable radiation fields. In turn, this allows to develop models and predict their behavior in complex radiation fields, such as those at laser-driven and FLASH facilities. TL and OSL detectors were irradiated at the Microtron MT25 electron accelerator in Prague, Czech Republic. GAFChromicTM films and plastic nuclear track detectors were used to study the beam profile and the neutron background respectively. The responses of the different detector to the pulsed mixed radiation fields of the Microtron MT25 are compared among each other and presented in this paper

The System for Control and Stabilization of the Beam Position in the Microtron MT-25 in Prague

A method of control the beam position at crucial points of the transport system and for the stabilization of its output position has been proposed and preliminary tested. The method is based on secondary electron emission from a thin metallic wire probe induced by electrons from the 25 MeV microtron. It was demonstrated, that magnetic field of the order of 0.2 T and parallel to the wire probe in front of the orifice of the extraction channel in the acceleration space, does not prevent the functioning of the method. A strong parasitic effect of secondary electron emission from the material of the channel and its support construction was found, leading to the inversion of the electron current polarity from the wire. This effect can be to great extent eliminated by negative electric potential bias relative to the channel. At the electron output current of 1 mA the secondary emission current from the wire probe of 0.3 mm diameter is of the order of several nA. Two electromechanical systems were designed for the removal of the probes from the beam path, to avoid the deterioration of the electron beam quality by scattering. Electronic schemes used for remote measurement of small probe currents, suppressing the influence of strong electromagnetic noise, are described. For stabilization of the output beam position two wire probes situated in air close to the Al output window were used. These probes having been placed at the periphery of the beam did not deteriorate the beam quality. The difference of their emission currents was used as an error signal to control the magnetic field of the last dipole, which kept the beam in the center of the output window.

Faraday Cup for Electron Flux Measurements on the Microtron MT 25

<p>The basic criteria for constructing of an evacuated Faraday cup for precise measurement of 5 to 25 MeV electron beam currents in air from a microtron are established. The Faraday cup, built in the microtron laboratory of the Faculty of Nuclear Sciences and Physical Engineering of CTU Prague, is described together with the electronic chain and its incorporation in the measuring line on the beam. Measures to reduce the backward escape of electrons are explained. The range of currents is from 10–5 to 10–10 A. The diameter of the Al entry window of the Faraday cup is 1.8 cm, and its area is 2.54 cm2. The thickness of the entry window is 0.1 mm.</p

Some Aspects of Profiling Electron Fields for Irradiation by Scattering on Foils

) for 1 mA of total beam current as functions of the distance from the beam exit window and of the thickness of the Al scattering foils

Filling and Recycling Apparatus of a Cyclotron Target with Enriched Krypton for Production of Radiopharmaceuticals

An apparatus for multiple filling of a cyclotron target with enriched Kr gas is described. The system is based on recycling pressurized gas by cryogenic pumping between the target tube and storage containers. The design and construction makes use of previous experience in the construction and operation of two analogue apparatuses for Xe¹²⁴ high pressure gas targets, but major modifications have been incorporated, evoked by the different physical properties of Kr, by the character of the nuclear reaction, and by the demand for automation from the side of the end user. <br /