Method of protecting a radiation detector in a charged particle instrument

Method of protecting a radiation detector in a charged particle beam apparatus, the apparatus including a source for producing a beam of charged particles, a condenser system including lenses for illuminating a sample, a projection system comprising including lenses for forming a magnified image of the sample on a detector system, the detector system including a radiation detector, the method comprising:

• exposing the detector to radiation using a first set of parameters, the set of parameters including condenser lens settings, projection lens settings, charged particle beam energy and beam current,
• predicting the flux density to which the detector will be exposed at a changed parameters before implementing said change in parameters, the prediction based on an optical model and/or a look-up table with one or more input variables from the group of condenser lens settings, projection lens settings, charged particle beam energy, beam current as input, and
• comparing the predicted flux density with a predetermined value, and, depending on the comparison, either
• Implement said change of parameters when the predicted flux density is below the predetermined value, or
• Avoid exposure of the detector to the flux density associated with the requested change in parameters when the predicted flux density is above the predetermined value.