Congresso del Dipartimento di Fisica Highlights in Physics 2005

1. Congresso del Dipartimento di Fisica Highlights in Physics 2005 11–14 October 2005, Dipartimento di Fisica, Università di Milano The thermoluminescence peaks of quartz at intermediate temperatures and their use in dating and dose reconstruction I. Veronese, A. Giussani and M.C. Cantone Dipartimento di Fisica, Università di Milano INFN – Sezione di Milano In collaboration with: SCOPE: TL dosimetry for evaluation of accidental dose using quartz extracted from recent building materials in urban settlements: assessment of the limits of the technique and of the minimum detectable dose. Basic studies of the glow peaks of quartz occurring in intermediate temperature range (150-250°C): measurement of the emission spectrum and determination of lifetimes and trap parameters. MATERIALS AND METHODS: • - Quartz extracted from recent building materials • Automated TL reader (Risø TL-DA-12) • Techniques for the total accrued dose assessment: regeneration dose and additive dose • - Techniques for the natural dose rate assessment: gamma spectrometry, beta dosimetry, alpha counting, flame photometry. - Pure quartz purchased from Merck Company - High Sensitivity spectrometer for 3D TL analysis - Secondary Standard Dosimetry Laboratory at GSF - Methods of glow curve analysis: Peak Shift (PS) and Isothermal Decay (ID) RESULTS: Fig. 2Example of recent building materials used for the study: roof tile samples with assumed age of 74 and 58 years respectively. In thermoluminescence dosimetry, the accidental dose Dx can be assessed as the difference between the total accrued dose DTL and the dose due to the natural sources of radiation absorbed by the sample during its age A: Accurate measurements of the terms contributing to Dx and of the uncertainties related to each of them were performed in order to establish the limits of the technique and the minimum detectable dose in a realistic scenario of accidental contamination. Fig. 1Spectral emission of pure quartz (3D vision and contour plot) in the temperature range of interest. Two main peaks (peak I and peak II) occur at approximately 135°C and 185°C (heating rate 1°Cs) respectively and for both of them the emission band is centered at approximately 380 nm. Fig. 3Variation of the relative uncertainty with the age of the sample for three selected values of Dx, assuming that DTL is evaluated with a typical uncertainty of 5%. The crossed area represents the situation when Table 1Trap parameters of peak I and II derived with the Peak Shift (PS) and the Isothermal Decay (ID) method. Table 2Lifetime values t of peak I and II at different temperatures. The values at 15°C were extrapolated considering the exponential relationship between t and the temperature. The dotted parts of the lines for Dx=10 mGy and Dx=20 mGy represent the case when the accrued dose is less than the chosen threshold of 40 mGy. REFERENCES: I. Veronese, A. Giussani, H.Y. Göksu, M. Martini – The trap parameters of electrons in intermediate energy levels in quartz.- Rad. Meas. 38, 743-6, 2004 I. Veronese, A. Giussani, H.Y. Göksu, M. Martini - Isothermal decay studies of intermediate energy levels in quartz – Radiat. Environ. Biophys. 43, 51-7, 2004 I. Veronese - The thermoluminescence peaks of quartz at intermediate temperatures and their use in dating and dose reconstruction. Tesidi dottorato in Fisica, Astrofisica e Fisica Applicata, Università degli studi di Milano, XVII Ciclo I. Veronese, A. Giussani, H.Y. Göksu- Limits of thermoluminescence dosimetry using quartz extracted from recent building materials in urban settlements – J. Env. Radioact. (accepted).