The quadrupole yokes are shaped with pole-tip extensions, which bring the quadrupole
fields 30 mm closer to the target. Also, to accommodate unrestricted detector
access at 135° to the beam, the yokes have cut-outs between poles for symmetric detector
ports. The cut-outs permit these ports to fit between coil windings, and four
cut-outs are used to maintain four-fold symmetry. The result is an effective working
distance of 80 mm despite a large yoke outer diameter of 270 mm and a bore of 14 mm [1,2].
A CSIRO-GEMOC Nuclear Microprobe quadrupole singlet showing these new design features, and developed as a collaboration
between the CSIRO and the MARC group of the University of Melbourne.
These new quadrupole
lens elements are being manufactured by, and are available through,
 C.G. Ryan and D.N. Jamieson, "A high performance quadrupole quintuplet lens system for the
CSIRO-GEMOC Nuclear Microprobe", Nucl. Instr. Meth. B158 (1999) 18-23.
 C.G. Ryan, D.N. Jamieson, W.L. Griffin, S.H. Sie, G. Cripps and G.F. Suter, "The new CSIRO-GEMOC
Nuclear Microprobe: A new highly integrated design for geoscience applications", proc.
10th Australian Conf. on Nuclear Techniques of Analysis, Canberra, ISSN 1329-8437 (1997) NTA/VSA8.