PHYSICAL CHARACTERIZATION BY GAMMA (Γ) ENERGY SPECTROMETRY OF DRESSED ILMENITE ORE SAND FROM SOUTHEAST MADAGASCAR (FORT DAUPHIN)

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1 PHYSICAL CHARACTERIZATION BY GAMMA (Γ) ENERGY SPECTROMETRY OF DRESSED ILMENITE ORE SAND FROM SOUTHEAST MADAGASCAR (FORT DAUPHIN) C. Miandrinandrasana* LIAC; Faculty of Sciences University of Antananarivo MADAGASCAR P. Rajaonera LIAC; Faculty of Sciences University of Antananarivo MADAGASCAR T. R. Randriamalala LNTPB, Antananarivo MADAGASCAR The physical characterization through gamma energy spectrometry of ore sand ilmenite sorted from the Southeast Madagascar was performed using detector Ge (Li). This analysis highlights the presence of Uranium, Thorium and Potassium through respectively the gamma ray detection of radionuclides of the radioactive family of Uranium-238, Thorium-232 and Potassium- 40 (K-40).The comparison study of activity of main gamma rays energy in the spectrogram with the international standards exemption level (ICRP) conclude that the sample contain a very low of radioactivity and shows no trace of artificial radionuclides 1. INTRODUCTION Through this physical characterization of gamma energy spectrometry we aim to highlight the presence of gamma emitting radionuclides which gives a material a radioactive character This characterization is very important because the mineral sands in this Southeast region as in most fields of this type in the world contain besides ilmenite a small amount of rare earths which may contain radioactive elements such as thorium, uranium, etc EXPERIMENTAL METHODS 2.1. Localization and sampling The South-east Madagascar (Fort Dauphin) is at present the area assigned to the Company QMM (QIT Madagascar Minerals) Rio Tinto to carry out the research and exploitation of ilmenite over three sites: the area Sainte Luce sector, Mandena sector and Petrika sector (see map in figure 1 and 2)[2].The samples are taken from of the mines of the Company Rio Tinto QMM.of Fort Dauphin [ coordinate (X = 120 Y = 454) according to Laborde system] *) Speaker Figure 1 Distribution of association Ilménite Monazite and Zircon deposits (Source : Service de la géologie-sigm, MEM) [2] Figure 2: Localization map of ilmenite ore sand Samples of QMM RIO- TINTO (Source : Service de la géologie-sigm, 1

2 2.2. Sample preparation and treatment Samples were from the minerals extracted and sorted out by Rio Tinto QMM from Mandena sector in Fort-Dauphin (see figure 1 and 2.). These samples were subjected to the following mining operations. - extraction (sand pumping and dredging) then physical separation of sand by mineral density difference - Electrostatic separation of conductive minerals from non-conductive minerals : production of ilmenite (the only conductive mineral) and magnetic separation of non-conductive minerals: zircon and sillimanite Products, such as ilmenite and zirsill are finally obtained. No chemical process is used 3. EXPERIMENTAL RESULTS OF ENERGY GAMMA SPECTROMETRY OF THE SOUTHEAST MADAGASCAR ILMENITE (FORT DAUPHIN) 3.1. Equipment and measuring instruments We determined the gamma energy spectrum of the ilmenite ore sample from Madagascar Southeast (Fort-Dauphin) by using a detector (Germanium) brand model GR Canberra Gamma energy spectrogram of Southeast Madagascar ilmenite (fort dauphin) The experimental results of analysis by physical characterization of energy gamma spectrometry of sample ore ilmenite from Southeast Madagascar (Fort-dauphin) are given and described by the gamma(γ) energy spectrogram spectra data I = f(e) E: Energy in Kev and I intensity in Cps (figure 3) Analysis of the gamma energy spectrogram of sand ilmenite from southeast Madagascar (Fort-Dauphin) The analysis of the spectrogram was carried out through the grading fittage of the peak energy followed by the identification allocation of the main lines To do so, the fittage results were compared with the main lines characteristic of the gamma transmitters of the radioactive family of Uranium U-238, Thorium Th-232 and Potassium K-40 given by the table of the catalogs of radionuclides Center Study of the Nuclear Energy J. F. Colard, J. P. Base, R. E. Duke (1988) [3] 3.4. Results of assignment and identification of the spectrum main gamma ray emission compared with the literature data [J. F. COLARD et al (1988)] [3] Table 1 summarizes the results of the analysis through fitting and gives the allocation of peaks and the identification of the radionuclides related to the main rays of the gamma transmitters from the ilmenite sample of Southeast Madagascar (Fort-dauphin) This table give the analysis of these spectra is given in tabular form, then a summary of the analysis in a comparative table including literature data and finally, the determination of gamma emitting elements existing in the samples and their respective activities (table 2, table 3 and table 4) 2

3 figure.3: Energy gamma spectrometry I= f(e en Kev) with allocation and assignment of lines and theorical energy Eth and experimental energy Eexp 3 Eexp=46,67 /Eth=46,5 kev/pb-210 / Pb-210/U-238 Eexp= 295,37kev/Eth=295,2kev/Pb-214/U-238 Eexp = 351,86kev / Eth=351,9kev / Pb-214 / U- Exp=582,96 kev /Eth=583,2 kev / Tl-208 / Th-232 Eexp=609,04kev/Eth=609,3kev /Bi-214 / U-238 Eexp=727,17kev/Eth=727,2kev / Bi-212 / Eexp=911,2kev/Eth=911,2 kev / Ac-228 / Th-232 Eexp=968,8kev/Eth=969,0 kev /Ac-228 / Th-232 E exp=1120,45kev/eth=1120,3kev/ Bi-214 / U-238 E exp=1460,53kev/eth=146,75kev / K-40 / Potassium-40 Eexp=1620,56kev/Eth=1460,75kev / Bi-212 / Th-232 Eexp=1769,5kev/Eth=1764,50kev / Bi-214 / U-238 Ex=186,10/Eth=186,1kev/Ra-226/U-238 Exp=238,63/Eth=238,6kev/Pb-212/Th-232 Eexp=2614,7/Eth=2614,50kev / Tl-208 /Th-232

4 Table 1. : Results of the fittage analysis and assignment of the gamma main rays emitted to the radionuclides corresponding to the spectrogram Our results Ilmenite sable sorted from Southeast Madagascar (Fort-Dauphin) 3.5. Interpretation and results The results of the analysis are given values summarizes in the following tables: - Potassium K-40 radioactive family : Theorical Result J. F. COLARD et col Assignement Peak Energy (Kev) Int. [3] Radionuclides N Energy Fit Centroid I E Int. Z Nuclide Period Family (Kev) (Kev) (Kev) (%) (Kev) (%) 01 46,54 46,68 46,67 0,004 46,5 4,05 82 Pb ,26 y U ,10 186,14 186,10 0, ,1 3,50 88 Ra y U ,63 238,85 238,63 0, ,6 43,60 82 Pb ,643 m Th ,21 295,37 295,37 0, ,2 19,20 82 Pb ,8 m U_ ,32 338,29 338,3 11,25 89 Ac-228 6,454* U ,92 351,85 351,86 0, ,9 37,10 82 Pb ,8 m U ,19 582,95 582,96 0, ,2 84,50 81 Tl-208 3,0527m Th ,31 609,06 609,04 0, ,3 46,10 83 Bi ,7 m U ,33 727,14 727,17 0, ,2 6,65 83 Bi ,600 m Th ,29 772, ,4 1,58 82 Ac-228 6,15 h* Th ,95 794, ,9 4,34 89 Ac-228 6,15 h* Th ,57 860, ,6 12,42 81 Tl-208 3,05 m* Th ,21 911,22 911,20 0, ,2 26,60 89 Ac-228 6,13 h Th ,97 969,11 968,97 0, ,0 16,17 89 Ac-228 6,13 h* Th , , ,45 0, ,3 15,00 83 Bi ,7 m U , ,53 0, ,8 10,67 19 K y K , , ,2 3,27 89 Ac-228 6,13 h Th , , ,56 0, ,6 1,51 83 Bi ,600 m Th , , ,64 0, ,5 15,90 83 Bi ,7 m U , , ,36 0, ,5 99,20 81 Tl-208 3,0527 m Th-232 Table 2: detected component of radionuclides of Potassium-40 radioactive family peak Energy (Kev) Activity Int. assignment N Exp. Th. (Bq. Kg -1 ) (Cps) radionuclide family , , K-40 Potassium-40 - Thorium-232 radioactive family : Table 3: detected component of radionuclides of Thorium-232 radioactive family Peak Energy (Kev) Activity Int. assignment N Exp. Th. (Bq.kg -1 ) (cps) radionuclide family ,63 238, PB-212 Thorium ,17 727, , , Bi-212 Thorium ,20 911, ,97 969, Ac-228 Thorium ,96 583, , , Tl-208 Thorium-232 4

5 - Uranium-238 radioactive family : Table.4: detected component of radionuclide of Uranium-238 radioactive family peak Energy (Kev) Activity Int. Assignment N Exp. Th. Bq.kg -1 cps radionuclide family 01 46,67 46, Pb-210 Uranium ,37 295, Pb-214 Uranium ,86 351, ,04 609, , , Bi-214 Uranium , , Spectrometric characterization of energy gamma (γ) mineral ilmenite southeastern Madagascar (Fort-Dauphin) has to find the energies of the families of thorium (Ac-228, Bi-212, Tl-208, Pb -212) and those of the family of U-238 (Pb-214, especially Bi-214) and the energies that characterize the potassium Comparison of main gamma ray emission spectrum compared with level exemption The following table (table 5) gives comparison with level exemption of main gamma ray emission of spectrum obtained through physical characterization by gamma energy spectrometry sample of ilmenite sand ore in Southeast Madagascar (Fort-Dauphin) Table 5: Results and comparison of activity with exemption level of the gamma ray energy spectrometry of Southeast Madagascar ilmenite sample [4] samples Family radionuclides Activity (Bq.kg -1 ) Exemption level Ilmenite from Southeast Madagascar (Fort-Dauphin) Potassium-40 K ± Ac ± 3 Thorium-232 Pb ± 1 Bi ± Tl ± 3 Pb ± 1 Uranium-238 Bi ± Pb ± 3 The table saw that the values of all the activities were all below the exemption level ( Bq.kg -1 for Potassium-40, Bq.kg -1 for the Thorium-232 and Uranium-238 according to the international standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources (Safety Series N 115, IAEA, 1997 )[4] 4. CONCLUSION The analysis through the physical characterization by gamma energy spectrometry of ilmenite sand from Southeast of Madagascar (Fort-Dauphin) has given the following results: - Highlight the presence of Uranium, Thorium and Potassium through respectively the gamma ray detection of radionuclides Lead Pb-214, Pb-210, Bismuth Bi-214 of the Uranium-238 radioactive family, Lead Pb-214 and 5

6 Pb-210, Bismuth Bi-214 of the Uranium-238 radioactive family and Potassium-40 of Potassium-40 (K-40) radioactive family - The comparison with the international standards exemption level shows that the sample contain a very low of radioactivity and no trace of artificial radionuclides Ackowledgments We thank: INSTN-Madagascar for laboratory measurements LNTPB Antananarivo, IRD-Madagascar and MADES Project Madagascar for their collaboration References [1] MIANDRINANDRASANA C.; RAJAONERA P. (2011) Contribution of extractive mineral industry (big mines valorization) through physical and chemical characterizing of ore sand mineral of ilmenite of southeast (Fort-dauphin) by RX Fluorescence spectrometry, by gamma (γ) energy spectrometry, by RX Diffraction spectrometry and granulometric analysis PhD thesis, DCMCP, Faculty of Sciences, University of Antananarivo (2011) [2] Service de la géologie-sigm, MEM) Plages et dunes de Madagascar SIGM, MEM [3] COLARD J. F., CULOT J. P., LEDUC R. E. (1988) Gamma-Ray Catalogue for radionuclides frequently detected in routine analysis Table of radionuclides arranged by increasing gamma-ray Energy; Centre d Etude de l Energie Nucléaire (CEN) /SCK-Mol, B- 2400Mol, Belgium, April 1988 [4] INTERNATIONAL ATOMIC ENERGY AGENCY (IAIEA)(1989), Measurement of radionuclides in food 6