Microtron MT25
The Prague microtron MT25 is a cyclic electron accelerator with Kapitza's resonator. The electrons are accelerated by an RF electric field of constant amplitude and frequency in a constant uniform magnetic field. In the vacuum chamber electrons follow circular paths with a common tangent point. The accelerating cavity, which is supplied with the RF field, is located at this point.
Schematic layout of the MT25 microtron:
1 – magnetron, 2 – phase shifter, 3 – circulator, 4 – water load, 5 – accelerating cavity,
6 – main magnet (vacuum chamber), 7 – electron trajectories, 8 – adjustable beam extractor, 9 – first deflector
Beam Parameters of Microtron MT25:
| Energy Ee: | Maximum 25 MeV, energy is variable in steps of 1 MeV from 12 up to 25 MeV or in steps of 0,5 MeV from 6 up to 15 MeV. The energy can be adjusted continuously in the range of step interval. |
| Output beam current: | Pulsed, pulse length is 3,5 µs, standard repetition rate is 423 Hz, mean maximum current is about 30 µA in dependence on electron energy. |
| Energy dispersion: | tens of keV |
| Beam distribution: | Electron beam line with magnetic lenses and deflectors to workstations A, B a C. |
| Beam diagnostician: | The mean electron current is measured by induction pick-up system before exit window of electron beam line, the beam position is indicated by a wire sensors. |
| Beam line output: | The thin Al window is placed on exit of electron beam. |
| Beam output: | The collimated beam spot dimension behind exit window is adjustable from 2 to 20 mm, the possibility of standard homogenous fields 10 × 10 cm2 in 1 m distance from exit window (homogeneity ±5%). |
| Beam power: | Ns = Is · Ee , for maximal energy and electron current it is about 750 W. |
| Dose rate: | About 100 Gy/(min·µA) in standard homogenous electron fields 10 × 10 cm2 at 1 m distance from exit window, in case of collimated beam it is several hunderds Gy/(min·µA). |
Photon beam - Bremsstrahlung
| Physical quality: | Bremsstrahlung is an electromagnetic radiation produced by the deceleration of electrons passed through tungsten (W) target placed behind exit window. |
| Energy spectrum: | Continuous, upper boundary of bremsstrahlung energy is equal electron energy Ee. |
| Photon output direction: | Rotary symmetrical towards electron motion before photon emission, photon beam is axial symmetric with forward intensity peak. The conical iron collimators are used for the homogenous photon fields (homogeneity better ± 5%). |
| Dose rate: | About 10 Gy/(min·µA) in axis of collimating beam in 1 m distance from tungsten target, about 0,5 Gy/(min·µA) in homogenous field 10 × 10 cm2 in 1 m distance. (E = 25 MeV) |
Neutrons
| Origin: | Photonuclear reaction (γ, n) or uranium photo fission. |
| Yields: | 2,5·1011 neutrons/s (Pb), 5·1011 neutrons/s (U), isotropic emission to all the solid angle. Proportion of bremsstrahlung dose to neutrons dose is about 2-10 %. |
| Energy spectrum: | in case of Pb it is up to 2 MeV, in case of U it is about 30% less |
Monitoring center of the MT25 microtron