Home > The cyclotron

A cyclotron is a particle accelerator made up of two horizontal hollow conducting half-cylinders called
" dees ", separated by a narrow interval.
Both " dees " plunge in a vertical uniform magnetic field. An alternative electric tension is applied between the two " dees ".

The students had to use the interactive terminal near the cyclotron and answer the questionnaire.

The cyclotron 

Do you know the cyclotron ?
Try the Quizz
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Download the questionnaire
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The cyclotron of the "Arts et métiers" Museum

The cyclotron exposed to the "Arts et métiers" Museum was used by Frederic and Irene Joliot-Curie who worked on the nuclear transmutation to the "College de France". Their research leads to discovered of the neutron.

  • the cyclotron has an energy of 7 MeV
  • the electromagnet weighs 25 tons (that exposed with the museum is factitious)


Cyclotron exposed in the Museum

The inventor of the cyclotron :

Lawrence Ernest Orlando (Nobel Prize 1939) built the first experimental cyclotron in 1929. But it is in fact in 1931 that the apparatus was really operational. It accelerated protons of energy 13 keV.

Constitution of a cyclotron :

- two electrodes in the shape of D (dee).
- a generator high frequency connected to the " dees ".
- a device to make the high vacuum in the cyclotron.
- a device sending ionized particles to the center of the cyclotron.
- an electromagnet creating an intense magnetic field.
- a channel of extraction to the end of which is the target.


alternating terminals + and -  


to the vacuum pomp

What for a cyclotron is using to ?

A cyclotron is used to accelerate particles charged and to produce isotopes.
The accelerated particles are ejected outside by a window to be then sent on targets.

It is used in research :

  • in nuclear physics in astrophysics
  • in chemistry for the synthesis of molecules labelled
  • in medicine for the production of isotopes used in tomography by emission of positon (T.E.P)

The maximum energy acquired by the particles is about 10 MeV (1 eV = J).

Principle of a cyclotron

The ions produced by the source are accelerated by an electric force under the action of a electrique field (q: charge of the particle). The particles are then deviated with a constant speed v, by a magnetic force under the action of a magnetic field and have half-circles trajectories with a radius and a angular velocity . This angular velocity is independent of energy.

The deviated ions are again in the area between the two " dees " and are again accelerated under the action of the electric field which was reversed. The kinetic energy of the particles increases with each passage between the " dees " and the radius of their circular trajectory increases successively. The maximum kinetic energy reached is
with : maximum speed attack and : useful maximum radius of the cyclotron

Other types of cyclotrons

Cyclotrons with separate sectors :
They are made up of 4 zones with field extremely separated by 4 zones without field.
(maximal energies : 1 GeV).


Synchrocyclotrons : These apparatuses make it possible to reach the energies raised until approximately 1 GeV. They require electromagnets of very big sizes and high masses (7 000 000 kg).

Synchrotrons : They are modern giant models of the cyclotrons which have several hundred meters of ray and which make it possible to obtain protons of energy of several GeV.
The L.E.P (Large Electron Positron Collider) is a collider of 27 km (16,8 miles) circumference which makes it possible to study the mutual annihilation of the electrons and the positrons. In the L.E.P, the particles are accelerated by an electric field and are deviated according to a circular trajectory thanks to a magnetic induction variable field.


Air sight of the site of the C.E.R.N on the border Free-Switzerland (picture C.E.R.N.)

Software of simulation of a cyclotron usable with scientific students

This software under DOS (87 KB in file zip) carried out by C Rivoisy is downloadable on the site of the academy of Nantes (France). Click on

This software makes it possible to simulate the trajectory of a positive particle of load equal to the elementary charge e and to modify the value of the magnetic field B, accelerating tension U, and its frequency f.



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