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We study the relationship between the iron abundance (IA) in red giant branch(RGB) stars and their radial distribution (RD) in Galactic globular clusters(GCs). We relied on publicly available archival data on IA in red giants (RGs)of GCs. We built a sample of ten target GCs in which the number of these RGsexceeded one hundred stars. In each GC of the sample, we compared the RDs oftwo sub-samples of stars, more iron-rich (IR) and more iron-poor (IP) than theclusters' mean values of [Fe/H]. Their RDs turned out to be different atstatistically significant confidence levels in NGC 104 (47 Tuc), NGC 1851, NGC3201, and NGC 6752 in the sense that the IP RGs were more centrallyconcentrated than their IR counterparts. In 47 Tuc, the difference issignificant at a higher confidence level within the PRAD of R = 8.0', where theIA increases by Delta[Fe/H] ~ 0.03 dex toward the cluster outskirts. In thelatter three GCs, Delta[Fe/H] ~ 0.05 dex. Interestingly, the V magnitude of theRGB bump and the horizontal branch was recently shown to fade outward in 47 Tucand was suggested to originate from a He abundance trend. The fading caused bythe IA trend is similar to that observed for the RGB bump. Although thedifference between the RDs of IP and IR RGs is statistically insignificant inother GCs, NGC 288 is the only GC of the sample, in which IR RGB stars areformally more centrally concentrated. Interestingly, three of the four GCs arehighly concentrated. (Abridged)

Unexpected radial trend of the iron abundance in a sample of monometallic Galactic globular clusters