A new technique for measuring positron impact direct ionisation

We present a method for measuring the electron yield in positron impact direct ionisation of atomic or molecular targets using a magnetically confined positron beam. This method can be used to determine the (relative) direct ionisation cross section. The use of this technique and a Surko trap based positron beam allows the electron yield to be measured at impact energies as low as 100 meV above the direct ionisation threshold. Application of this technique to the measurement of the energy dependence of the direct ionisation cross section near threshold is also discussed.