http://www.fe.infn.it/u/mantovani/CV/Proceedings/Puccini_10b.pd

A. Puccini

D. Sechi

F. Mantovani

G. Oggiano

G. Xhixha

S. Cuccuru

S. Mariani

MANTOVANI, Fabio

XHIXHA, Gerti

Archivio istituzionale della ricerca - Università di Ferrara

Natural radioactivity in Sardinian granite dimension stones

552SESSIONE 16Key words: Dimension stones, gamma-ray portablespectrometer, granites, radioactivity, Sardinia-Corsicabatholith.INTRODUCTIONAbout 6000 km2 of Sardinia consist of the Sardinia-Corsicabatholith made up of several plutons emplaced between 311 and286 Ma (OGGIANO et alii, 2005; GAGGERO et alii, 2007). Thewide emplacement time-span allowed large compositionalvariability of these intrusions, which range from quarzodiorites-tonalites to leucomonzogranites. These stones represent aconsiderable economic resource; the first evidence of itsexploitation dating back to the 15th century BC in the building of nuraghi. Moreover the Roman quarries, active during the Roman Empire and still visible on the north eastern coast (POGGI &LAZZARINI, 2005).Nowadays, granite quarrying activity is located in the central-north Sardinia, mainly in Gallura and Goceano regions, whereseveral commercial varieties are exploited. All these stones are widely exploited and represented the main building materials in the past. Besides, these granites have beenwidely exported around the world as tiles, flooring, columns orother architectonic element. Moreover the north-eastern Sardiniagranite was largely employed for ashlars used in the building ofdwellings until the sixties. Taking into account the large diffusion of the Sardinian granites, the knowledge of their naturalradioactivity is basic for the evaluation of the amount of publicexposure because people spend most of their time (about 80%)indoor (NGACHIN et alii, 2007 and their references).The aim of this work is therefore to determine the K, U andTh isotopic concentration in these materials.METHODSFor this purpose a portable gamma-ray spectrometer at theNational Lab of Legnaro (INFN) was developed (Fig. 1).The equipment consists of one liter thallium-activated sodiumiodide scintillator [NaI(Tl)], digiBASE by Ortec and a netbookwhich manages also humidity and temperature sensors. By usingthe Jradview software is possible to process the data in real timeand to determine uranium and thorium (in ppm), expressed asequivalent units, and potassium concentration (in %) as well astotal activity expressed in Bq kg-1. Following the IAEA guideline (IAEA-TECDOC-1363, 2003), the gamma-ray spectroscopicanalysis is performed by monitoring three spectral windows:1.37-1.57 MeV for 40K, 1.66-1.86 MeV for 214Bi and 2.41-2.81MeV for 208Tl.The concentrations of U/Th are estimated by 214Bi/208Tldecays, under the assumption that the U and Th decay series arein secular equilibrium. This occurs when the parent half life ismuch longer than the daughter half life and then the number ofatoms of a daughter isotope essentially becomes constant aftersome time. Two conditions are necessary for secular equilibrium.First, the parent radionuclide (238U/232Th) must have a half-lifemuch longer than that of any other radionuclide in the series.Second, a sufficiently long period of time must have elapsed, toallow for ingrowth of the decay products. The state of secularNatural radioactivity in Sardinian granite dimension stonesANTONIO PUCCINI (*), STEFANO CUCCURU (*), DANIELE SECHI (*), GIACOMO OGGIANO (*),FABIO MANTOVANI (°), GERTI XHIXHA (°) & SARA MARIANI (**)_________________________(*) Dipartimento di Scienze Botaniche, Ecologiche  e Geologiche –Università di Sassari, apuccini@uniss.it(°) Dipartimento di Fisica – Università di Ferrara(**) Centro di Geotecnologie – Università di SienaFig. 1 – Portable  gamma-ray spectrometer in a quarry during theacquisition of K-U-Th isotopic concentration.553SESSIONE 16equilibrium in natural U and Th ores is significantly altered when they are processed to extract specific radionuclides, in particularRa and Rn.Assuming secular equilibrium, in order to evaluate theexternal gamma-radiation dose from building materials, thefollowing model (HAYAMBU et alii, 1995) was used as criterion.This model uses the External Hazard Index (Hex) defined as:Hex= AU/370 + ATh/259+AK/4810where AU, ATh and AK are the activity concentration of 238U,232Th and 40K, respectively, in Bq kg-1 in building materials. Tolimit the external gamma radiation dose from building materialsto 1.5 mSv year-1, Hex must be less than unity in order to maintain the radiation hazard negligible (XINWEI, 2004).The average radioactivities of 238U, 232Th and 40K and Hexmeasured in different commercial varieties of Sardinian granitesare given in Table 1.RESULTS AND CONCLUSIONSThe data acquires show that the 40K average activities varyfrom 925±110 Bq kg-1 in Grigio Malaga to 1501 Bq kg-1 in Rosa Cinzia. The 238U, average activities range from 38±8 Bq kg-1 inGrigio Perla to 77±18 Bq kg-1 in the San Giacomo. The highestaverage activity of 232Th was 91±15 Bq kg-1 in Ghiandone and the lowest average was 59±5 Bq kKg-1 in Rosa Beta. About the Hex, the commercial varieties showed the highestvalues were, in order, Ghiandone (0.83±0.11), Rosa Cinzia (0.82)and San Giacomo (0.79±0.13).Finally, all commercial investigated varieties have Hex valuebelow 1, hence, generally, the corresponding rocks can be safelyused as building materials for dwelling construction also inindoor conditions.REFERENCESGAGGERO L., OGGIANO G., BUZZI L., SLEJKO F. & CORTESOGNOL. (2007) - Post-Variscan mafic dykes from the late orogeniccollapse to the Tethyan rift: evidence from Sardinia. Ofioliti32, 15-37.HAYAMBU P., ZAMAN M.B., LUBABA N.C.H., MUNSANJE S.S.,MULEYA D. (1995) – Natural radioactivity in Zambianbuilding materials collected from Lusaka. J. Radioanal. Nucl.Ch., 199 (3), 229-238.IAEA-TECDOC-1363 (2003) - Guidelines for radioelementmapping using gamma ray spectrometry data.NGACHIN M., GARAVAGLIA M., GIOVANI C., KWATO NJOCK M.G.NOUREDDINE A. (2007) – Assessment of natural radioactivityand associated radiation hazards in some Cameroonianbuilding materials. Radiat. Meas., 42, 61-67.OGGIANO G, CHERCHI G.P., AVERSANO A., DI PISA A., ULZEGAA., ORRÙ P. & PINTUS C. (2005) – Note illustrative dellaCarta Geologia d’Italia. Foglio 428 Arzachena, S.EL.CA,Firenze.POGGI D. & LAZZARINI L. (2005) – Il granito sardo: cave ecavatura. Usi, diffusione e aspetti archeometrici. Marmora, 1,49-68.XINWEI L. (2004) – Natural radioactivity in some buildingmaterials and by-products of Shaanxi, China. J. Radioanal.Nucl. Ch., 262, 775-777.Tab.1 – Commercial varieties considered and mean values of A40K , A238U, A232Th, Total Activity and Hex (About Rosa Cinzia, was not calculated the uncertainty because we performed only a single measure)CommercialvarietiesMeasuresnumberActivity 40K(Bq/kg)Activity 238U(Bq/kg)Activity 232Th(Bq/kg)Total Activity (Bq/kg) HexRosa Cinzia 1 1501 75 79 1655 0.82Ghiandone 7 1361±106 74±14 91±15 1526±108 0.83±0.11San Giacomo 2 1473±108 77±18 71±14 1621±111 0.79±0.13Grigio Malaga 4 925±110 39±6 68±2 1032±110 0.56±0.04Grigio Perla 10 1288±133 38±8 67±11 1393±133 0.63±0.06Bianco Sardo 3 1351±72 49±12 60±7 1460±73 0.64±0.06Rosa Beta 4 1183±110 43±11 59±5 1285±110 0.59±0.07

http://www.fe.infn.it/u/mantovani/CV/Proceedings/Puccini_10b.pdf

Natural radioactivity in Sardinian granite dimension stones

Abstract

Similar works

Full text

Available Versions

Archivio istituzionale della ricerca - Università di Ferrara

Archivio istituzionale della ricerca - Università di Ferrara