A wide-angle magnetic spectrograph of a novel design

Abstract At the 5 MV tandem accelerator of the CMAM we install a UHV magnetic spectrograph for the detection of scattered and recoiled ions. Its special feature is that the ions emerging from the sample are passing through a 4 nm thick DLC foil before entering the spectrograph. The secondary electrons emerging from this foil upon passage of an ion are focused on a two-dimensional position sensitive multi-channel plate (MCP) detector with delay-line read-out. From their impact position on this detector the direction of the ion is determined with a precision of 0.15° within an elliptical cone of 6° × 9°. The spectrograph, consisting of a 115° sector magnet with special shaped pole faces, focuses the ions onto a one-dimensional position sensitive MCP detector, also with delay-line read-out, in the focal plane of the magnet. The time delay of the coincident pulses in the first and second detector is measured so that the velocity v of the ion is known in addition to the magnetic rigidity mv / q , allowing determination of m / q . The energy resolution is determined by the straggling in the foil and amounts to Δ E / E  ≈ 10 −3 for 2 MeV α particles. Blocking patterns of scattered or recoiled ions can be measured in one run. Because of the ion identification implied in the system, recoil spectra can be generated with light ions used as projectile.