The new Melbourne nuclear microprobe system D.N. Jamieson a, * , B. Rout a , R. Szymanski a , P. Spizzirri a , A. Sakellariou a,1 , W. Belcher a , C.G. Ryan b a School of Physics, Microanalytical Research Centre, University of Melbourne, 3010 VIC, Australia b CSIRO, Division of Exploration and Mining, North Ryde, NSW 2113, Australia Abstract Thespatialresolutioninanuclearmicroprobesystemhasbeenstalledataround1 lmformanyyears.InMelbourne wearepresentlyconstructinganewfacilitywhichaimstobreakthisbarrier.Thekeyingredientsofthenewfacilityare: (i)anovelmagneticquadrupolelensquintupletprobeformingsystemthatisafurtheroptimisedversionoftheCSIRO/ MARC system presently in operation in Sydney, (ii) high solid angle detectors for particles, X-rays and secondary electrons and (iii) a fast data acquisition system able to cope with greater than 20 kHz count rates from up to four detectors with full deadtime correction. This paper describes the optimised probe forming lens system which is com- prised of four thin lenses and one thick lens to produce an orthomorphic probe forming lens system with a demag- nification of 150. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 41.85.Lc; 42.60.Jf; 79.20.Rf; 68.37.d Keywords: Nuclear microprobe; Quadrupole lenses; Probe forming lens system; Beam brightness 1. Introduction The design considerations necessary to con- struct a nuclear microprobe with a significantly better resolution than 1 lm were presented at the recent 7th International Conference on Nuclear Microprobe Technology and Applications, held in Bordeaux [1]. The new CSIRO/MARC five lens system[2]addressesmanyoftheseconstraintswith its high demagnification lens system comprising magneticquadrupolelensesofanoveldesign.This system has performed very well, allowing high beam currents to be focused into small spots. The new system has been applied to detailed studies of geological materials [3,4] where the intense beam spots have provided images of trace element dis- tributions with sensitivities at the parts per billion level. We describe further modifications and devel- opmentsofthissysteminthenewsystempresently under construction in Melbourne. We have devel- oped this new system recognising the detailed considerations discussed in the earlier review [1]. We also recognise that to exploit the unique ca- pabilitiesofionbeamanalysisforimagingrequires Nuclear Instruments and Methods in Physics Research B 190 (2002) 54–59 www.elsevier.com/locate/nimb * Corresponding author. Tel.: +61-3-8344-5376; fax: +61-3- 9347-4783. E-mail address: dnj@physics.unimelb.edu.au (D.N. Jamie- son). 1 Present address: Department of Applied Mathematics, ResearchSchoolofPhysicalSciencesandEngineering,Institute ofAdvancedStudies,AustralianNationalUniversity,Canberra ACT 0200, Australia. 0168-583X/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0168-583X(01)01201-0