Building materials as a source of gamma radiation and radon concentration: tests and improvement of experimental methods

INTRODUCTION The Italian national survey on natural radioactivity in dwellings showed that in the central and southern part of Italy the widespread use of building materials of volcanic origin (tuff and pozzolana) has two important consequences: high levels of radon concentration indoors and the presence of elevated γ dose rates (1,2,3). The significant role of some building materials as a source of natural radiation has led the authors to develop a method to characterise them in buildings. In fact, preventive assessment of building materials to decide whether or not they are appropriate for use in construction can be relatively simple in the laboratory with suitable procedures of gamma spectroscopy. Indeed, some computational models (4,5,6,7) have been formulated to calculate the indoor gamma dose rate from the activity concentration of the building materials. Taking a sample from an existing building for an accurate laboratory analysis, however, is clearly not practical. In order to overcome these problems, the authors developed a new method to evaluate the characteristics of building materials as gamma ray and radon sources in the field (8,9). This was done combining the results of in situ measurements (gamma spectrometry (10) and gamma dose rate assessment) and the computational estimates of the Markkanen room model (4). The method makes it possible to assess activity concentration in the walls of a room without having to measure a sample in the laboratory by gamma spectrometry. Shown to work well in a real situation, other experimental tests and a sensitivity analysis were performed to assess the uncertainties in the estimates. In this paper, the results of these tests are presented and an evaluation of the uncertainties discussed. The method also estimates the radon exhalation from walls.