1 Investigation of x-ray shielding properties of concrete containing different percentages of recycled lead shots. M. Alnajjar 1 , S.Yassin 2 , S. Shihada 1 1 Department of Civil Engineering, Islamic University Of Gaza, Palestine. 2 Department of Physics, Islamic University Of Gaza, Palestine. Key words Recycle Lead, X-ray, Lead Shots, Concrete, Compressive Strength. Abstract Recycled lead in shot form with maximum radius of 1.18 mm to concrete constituents in different percentages of lead-to-cement ratio (20% to 140%) by weight were added and investigated in this study. Several tests on fresh and hardened concrete were carried out. The fresh concrete was tested for slump and workability. The testsof hardened concrete included compressive strength at 7 days, 14 days, and 28 days. The penetration of x-ray to concrete after 14 days from casting date was done using a basic x-ray machine as source at 100KeV and 120KeV energies and used x-ray Dosimeter STEP OD-01 as detector to measure the radiation dose rate (µsv/h) that penetrated the concrete samples. Then, linear attenuation coefficients (LAC) and compressive strength of concrete specimens were experimentally investigated. By comparing the obtained data from concrete specimens with and without lead, it was observed that, if the recycled lead shots to cement ratio is about 80% by weight of cement is added to the concrete mixes, the concrete can be used as a suitable shield against x- rays. Introduction The radiation dosimetry is an important subject in physics, as the radiation started to be used in various fields with the development of technology. Regardless of the many benefits that come from the application of radiation, it is hazardous for human cells, which should be protected. This can be made possible by applying three main methods namely time, distance and shielding in a proper way. The latter is the mostused method especially for critical buildings such as Radio-Diagnostic Centers. Heavy elements such as lead or tungsten are ideal materials for use in radiation shielding. However, these materials cannot be used