A combination of deltaE-E gas ionisation chamber and time-of-flight technique for heavy ion ERDA

A new TOF-energy telescope was installed at the ERDA beamline of the Rossendorf 5 MV tandem accelerator. The TOF-system consists of a small MCP-start-detector using a 45° tilted C-foil and a large mirror-type MCP-stop-detector with a flight path of about 100cm. In order to reduce the energy straggling of recoils in the start and stop detector diamond-like carbon (DLC) foils with thicknesses in the range of 0.5 up to 1.0 mg/cm2 are used. The energy detector is a large solid-angle DE-E gas ionisation chamber. This chamber is position sensitive in the scattering plane and enables kinematic correction. The total solid angle of this TOF- energy telescope amounts to about 3.2 msr and is mainly limited by the size of the stop-MCP. The most important features and advantages of this combination are as follows:

• In contrast to conventional Si- energy detectors the ionisation chamber suffers no damage by heavy particles.
• The ionisation chamber enables very easy a kinematic correction in the range of ±0.05° of the scattering angle.
• There are different options to separate the detected particles according to their mass or to their atomic number and to use the energy information from the ionisation chamber or from the TOF.

Data for energy- and time- resolution and the resulting values for depth- and mass- resolution are given and the limiting parameters of the telescope are discussed. ERDA-spectra and resulting depth profiles obtained with 35 MeV Cl-ions at thin multilayer structures will be presented demonstrating the properties of this telescope.