A charged particle system, comprising: a charged particle column for focusing a primary charged particle beam onto the surface of a target, wherein the impact of the charged particle beam with the target induces emission of secondary charged particles (118, 119, 120, 152) from the target; and a charged particle detector assembly including: a detector (210, 310, 410, 510, 934, 1034) for producing an electrical signal corresponding to the number of charged particles impacting the detector; characterized in that the charged particle detector assembly comprises: a multiplicity of concentric annular collection grids (222, 224, 226, 228, 522, 524, 526, 528, 822, 824, 826, 828, 932, 933) or at least one resistive grid, positioned between the charged particle detector and the surface of the target for causing secondary charged particles to move from the target to the detector, the multiplicity of annular collection grids in operation being maintained at different potentials or different potentials being maintained on the different parts of the at least one resistive grid to provide a radial field that deflects the secondary charged particles to spread the secondary charged particles more evenly over the detector to reduce the maximum current density of the secondary charged particles impinging on the charged particle detector, thereby prolonging the useful life of the charged particle detector. a charged particle column for focusing a primary charged particle beam onto the surface of a target, wherein the impact of the charged particle beam with the target induces emission of secondary charged particles (118, 119, 120, 152) from the target; and a charged particle detector assembly including: a detector (210, 310, 410, 510, 934, 1034) for producing an electrical signal corresponding to the number of charged particles impacting the detector; characterized in that the charged particle detector assembly comprises: a multiplicity of concentric annular collection grids (222, 224, 226, 228, 522, 524, 526, 528, 822, 824, 826, 828, 932, 933) or at least one resistive grid, positioned between the charged particle detector and the surface of the target for causing secondary charged particles to move from the target to the detector, the multiplicity of annular collection grids in operation being maintained at different potentials or different potentials being maintained on the different parts of the at least a detector (210, 310, 410, 510, 934, 1034) for producing an electrical signal corresponding to the number of charged particles impacting the detector; characterized in that the charged particle detector assembly comprises: a multiplicity of concentric annular collection grids (222, 224, 226, 228, 522, 524, 526, 528, 822, 824, 826, 828, 932, 933) or at least one resistive grid, positioned between the charged particle detector and the surface of the target for causing secondary charged particles to move from the target to the detector, the multiplicity of annular collection grids in operation being maintained at different potentials or different potentials being maintained on the different parts of the at least a multiplicity of concentric annular collection grids (222, 224, 226, 228, 522, 524, 526, 528, 822, 824, 826, 828, 932, 933) or at least one resistive grid, positioned between the charged particle detector and the surface of the target for causing secondary charged particles to move from the target to the detector, the multiplicity of annular collection grids in operation being maintained at different potentials or different potentials being maintained on the different parts of the at least one resistive grid to provide a radial field that deflects the secondary charged particles to spread the secondary charged particles more evenly over the detector to reduce the maximum current density of the secondary charged particles impinging on the charged particle detector, thereby prolonging the useful life of the charged particle detector.