metal-poor IM-AGBs play only a minor role in the production of Pb though for their 5 M$_\odot$ model, the Pb yields do not change between \[Fe/H\] = $-$1.3 and solar. @herwig04 suggest that metal-poor IM-AGBs efficiently activate the $^{22}$Ne neutron source though quantitative $s$-process yields are not presented. @busso01 predict high yields of Pb from metal-poor IM-AGBs. The ratio of Pb/La and Pb/Ba can be used to probe the nature of the $s$-process in metal-poor AGB stars [@gallino98; @goriely00]. Numerous observational studies have found considerable overabundances of Pb in stars that exhibit large $s$- and/or $r$-process enhancements (e.g., @cowan96 [@sneden00c; @aoki00; @aoki01; @aoki02; @vaneck01; @vaneck03; @johnson02a; @lucatello03; @sivarani04; @ivans05] and references therein). If the globular cluster star-to-star abundance variations are due to pollution from metal-poor IM-AGBs, we may expect large overabundances of Pb and a dispersion in Pb abundances despite the absence of variations and excesses in other $s$-process elements.

In this paper, we present measurements of Rb and Pb in the globular cluster NGC 6752 as well as measurements of Pb in the globular cluster M 13. While Rb has been measured in two globular clusters, $\omega$ Cen [@smith00] and NGC 3201 [@gonzalez98], as far as we are aware 