Alpha radioactivity in Indian cement samples

Background: The essential constituents of cements like lime, silica and alumina are derived from earth’s crust in which radioactive elements like uranium, thorium etc are also present in varying amounts almost everywhere. These two elements are considered as the parent elements of uranium and thorium radioactive decay series in which radon and thoron are produced respectively as decay products. In the present study the samples of ordinary Portland cement (OPC), Portland pozzolana cement (PPC) and some other cementious finishing materials like white cement, Plaster of Paris (POP), cement putty etc were collected and analysed for radium and radon concentrations along with radon exhalation rates. Materials and Methods: Alpha sensitive LR-115 Type II plastic track detectors commonly known as “Solid State Nuclear Track Detectors” were used to measure the radium and radon concentration. The alpha particles emitted from the radon causes the radiation damaged tracks. The Chemical etching in NaOH at 60 ° C for about 90 minutes was done to reveal these latent tracks, which were then scanned and counted by an optical microscope of suitable magnification. By calculating the track density of registered tracks, the radon and radium concentrations along with exhalation rate of radon, were determined using required formulae. Results: The radon and radium concentration in various brands of cements found to vary from 333 ±9.9 to 506 ±13.3 Bq m–3 and from 3.7 ± 0.1 to 5.6 ± 0.2 Bq kg–1 while in various cementious finishing materials used in the construction, these were found to vary from 378 ±19.7 to 550 ± 9.8 Bq m–3 and from 4.2 ± 0.2 to 6.1 ± 0.1 Bq Kg–1, respectively. Based on the data the mass and surface exhalation rates were also calculated. Conclusion: The measurements indicate that there is marginal variation of the concentration of radium and radon in various brands of cements in India with lower levels in the cement samples having red oxide and higher levels in fly ash based cement samples but overall concentration levels of radon and radium are lower than that of average global values.