Apparatuses and methods for ananlysing charged species

摘要

A beam 10 of charged particles, such as ions, are analysed using a system including a gate having entrance and exit positions separated by a distance S, the gate being switchable between open and closed states allowing or preventing charged particles from passing through. The gate is periodically switched at a frequency F, and a duty cycle x expressed as a ratio. The average kinetic energy U(α) of a particle within the gate can be controlled by varying a parameter α of the system. A time�averaged collection current I from charged particles exiting the gate is measured as α is varied, and a discontinuity in the derivative of the current I at a given value of α indicates the onset of a current component attributable to a charged species of mass m entering the gate. The mass m is determined from the relationship: where Um(α) is the value of U(α) at which said discontinuity in the derivative of the current is determined.