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Linear accelerators

The linear accelerators available are two clinical accelerators and a research accelerator with two irradiation set-ups. So a total number of four iradiation set-ups are available for investigations in the field of clinical dosimetry or dosimetric fundamental research.

Clinical accelerators

The two clinical accelerators of type Elekta Precise Treatment SystemTM can generate high-energy photon radiation with nominal accelerating voltages between 4 MV and 25 MV and electron radiation with energies between 4 MeV and 22 MeV. One accelerator is equipped with a multileaf collimator. Using this accelerator investigations in very small or irregularly shaped beams, as they are used for instance in Intensity Modulated Radiation Therapy (IMRT), can be done. Such radiation fields, which deviate significantly from the standardized reference fields, are increasingly used in the framework of new irradiation modalities; the importance of dosimetry in such fields is therefore increasing.

A water phantom containing an ionization chamber in front of a clinical accelerator of the type Elekta Precise Treatment SystemTM. The green laser lines are used to align the ionization chamber.

Water calorimeter in front of the clinical accelerator. The calorimeter is the primary standard measuring device for the unit of the absorbed dose to water in high-energy photon and electron beams.


Parameters of the clinical beams



Radiation qualities
Photons (MV): 4, 6, 8, 10, 15, 25
Electrons (MeV): 4, 6, 8, 10, 12, 15, 18, 20, 22


Dose rates
Photons: 0,2 Gy/min to 5 Gy/min
Electrons: < 4 Gy/min


Radiation field size
Rectangular diaphragms: 0,5 cm x 0,5 cm to 40 cm x 40 cm
Multileaf collimator: any shape up to 40 cm x 40 cm


Pulse dose rates
Photons: < 70 Gy/s
Electrons: < 420 Gy/s
Pulse repetition frequency: 25 Hz to 400 Hz
Pulse width: 3 µs

Research accelerator

The linear accelerator (11 m in length) for dosimetric fundamental research has been custom-built for PTB. The energy of the accelerated electrons can be varied continuously from 0.5 MeV to 50 MeV; the electron beam power is up to 1 kW. A total of two irradiation set-ups are available which allow irradiation with electron energies in the range 0.5 MeV to 10 MeV and 6 MeV to 50 MeV, respectively.

Electron linear accelerator (11 m in length)

The properties of the electron beam, as for instance the beam position, beam profile, spectral electron fluence or the beam current can be measured. Therefore, in the field of fundamental research, radiation effects can be studied as a function of these fundamental physical quantities of electrons.

Spectrometer for measuring the spectral electron fluence.


Parameters of the electron beams in the research section


Energy range: 0.5 MeV to 50 MeV

Energy width
0.5 MeV < E < 5 MeV: ≥ 4 keV
5 MeV < E < 20 MeV: ≥ 20 keV
E > 20 MeV: ≥ 40 keV
Energy drift: < 0.05 %/h
Beam diameter: < 3 mm
Beam position stability: ± 0,3 mm

Beam power
Maximum: 1 kW
0.5 MeV to 10 MeV: ≥ 1 W
6 MeV to 50 MeV: ≥ 100 W
Pulse repetition frequency: 1 Hz to 100 Hz
Pulse width: 3 µs
Pulse current: < 200 mA
Scan frequency: 0 Hz to 10 Hz