Abstract
In this study, the levels of natural radioactivity in the groundwater samples collected from 26 different locations in Al-Zulfi, Al-Qassim and Al-Majmaah regions were determined. The estimated average values of Ra-226, Ra-228, K-40, gross and gross activities in the samples were 0.87BqL(-1), 1.33BqL(-1), 4.22BqL(-1), 36.82mBqL(-1) and 831.91mBqL(-1), respectively. We found that age-dependent effective ingestion dose from radionuclides in all samples were higher than WHO recommended levels of 0.1 mu Svy(-1) for adults 0.2 mu Svy(-1) for children and 0.26 mu Svy(-1) for infants while 20 sampling locations have age-dependent effective dose equivalent from contributors were higher than WHO recommended level of 0.1mSvy(-1).