Project / Nuclear

Cyclotron

A cyclotron is a particle accelerator in which ions are accelerated as they orbit in a magnetic field. In the simplest form it consists of a uniform magnetic field, B. The circular area is divided into two D-shaped regions ("dees"), one of which is held at earth potential while an alternating potential is applied to the other. Ions produced in an ion source near the centre of the area travel in circular orbits. As they cross the gap between the two dees they gain energy from the potential difference and so the radius of their orbit increases. Ions spiral outwards, acquiring energy on each orbit, until at the outside of the cyclotron they reach their full energy.

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A switching magnet directs the beam in one of 12 possible directions. One of these directions leads to a radiation box, held in place by a robot. The target of the irradiation experiment is placed inside this box. 

The robot has two motors at 90 degrees. One moving the box up and down, the other left and right. The robot moves the box through the beam (which is only 1cm2) at constant velocity, so that the samples inside are irradiated evenly.

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The Birmingham Facility

The Birmingham MC40 Cyclotron is situated in the School of Physics and Astronomy at Birmingham University and has been in operation since 2004.

The primary function of the cyclotron is the production of radio-isotopes for use in medical imaging but is also used for general research.

Although the cyclotron can produce a range of ions at various energies, for irradiation studies of materials for the HL-LHC we are interested in using protons at an energy of 26-27 MeV.

Although this energy is an order of magnitude less than the energy of the beams in use at the CERN irradiation facility, the required fluence is measured in units of 1 MeV neutron equivalents (1MeV neq).

This means that the Birmingham Cyclotron can irradiate the silicon samples to HL-LHC fluences, equivalent to that at the CERN facility, in 80 seconds per cm2.

A comparison between charge collection measurements of a sensor irradiated at Birmingham and other irradiation facilities is presented below, with comparable results.

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