[en] Verification of lead equivalence thickness of radiation room and shielding material such as personal protective clothing are crucial to ensure that they fulfill their task in protecting patient and personnel as well as the member of public from ionizing radiation. The radiation room or shielding materials need to be verified according to Ministry of Health (MOH) requirements comply with a current standard. The thickness of the shielding materials is determined using direct comparison between the attenuation of X-ray or gamma ray by the shielding materials and high purity lead sheets (99.99 %). Currently Americium-241 is used to measure the thickness of the shielding materials for diagnostic X-ray room due to the gamma energy of 59 keV which is adequate to measure the thickness of 2 mmPb. However, the uncertainties of thickness getting higher for a thicker shielding materials due to so called a build-up factor. Various sizes of collimator and stronger radiation source were used to reduce the build-up factor and improve the accuracy of the lead equivalence thickness. From the measurement the accuracy of the thickness were increased when using a narrow beam and a stronger radiation source. (author)