VAMOS Ionisation Chamber
The VAriable MOde Spectrometer, VAMOS, is a collaboration to build a large acceptance spectrometer for identifying products of reactions.
VAMOS is located at the SPIRAL facility at GANIL.
The ionization chamber is designed to measure the energy loss of particles arriving at the focal plane of VAMOS. The particles pass through the detector in the region between the cathode and the Frisch grid and the electrons they liberate in the gas volume pass through that grid as they drift towards the anode. The anode is divided into three sections along the flight path of the particles. The first two sections give independent measurements of the energy loss of the particles and comparison of these signals can be used to reject events in which the particles undergo Rutherford scattering in the gas while under the energy loss electrodes.
Except for light energetic ions, the chamber is normally operated at a gas pressure that causes the particles of interest to be stopped within the detector and to deposit about 70% of their energy under the first two electrodes as this has been shown to give the best Z resolution. The anode is also split into segments across the focal plane. This allows the chamber to be used at higher rates since recoils entering the chamber simultaneously but under different segments of the anode can be processed in different amplifiers. The ionization chamber is used in association with two position detectors just upstream. Depending on the experiment these may be either drift chambers or secondary electron emission detectors. The second of the drift chambers is in some cases mounted directly onto the front of the ionization chamber without a window in between to give minimal energy loss for heavy-ions.