A study to determine the concentration and emanation rate of Radon-222 were done inside Gua Gajah and Gua Penyu limestone caves, Kompleks Gua Kota Gelanggi, Pahang, Malaysia to find the link between ventilation and annual effective dose. Gua Gajah has two major openings and features uneven earth surface unlike Gua Penyu which has single entrance and smooth passage way. Dosimeters with CR-39 solid state nuclear track detector (SSNTD) were distributed 15 m apart. For emanation rates, dosimeters

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... re embedded about 5 cm into cave floor while for concentration measurements, they were placed 1 m above ground. The control samples were placed in front of the main entrance. The samples were left and collected after 30 days. Every CR-39 samples were etched with 6M NaOH solution with 70 ᵒC for 6 hours in water bath and observed under microscope of 200x linear magnifications to calculate tracks densities. Results indicated that the average Radon-222 emanation rate inside Gua Gajah was higher than that of Gua Penyu. On the other hand, the average concentration of Radon-222 inside Gua Gajah was lower than that of Gua Penyu. The average annual effective dose of Radon-222 in Gua Gajah and Gua Penyu was 0.084 mSv yr -1 and 0.12 mSv yr -1 , respectively. These findings point out that ventilation contributed by cave openings plays an important role in reducing the indoor radon gas accumulation, thus lowering the annual effective dose.