Establishment of Radiometric Maps of the Southern Region of .

HF Randriantseheno *, Raoelina Andriambololona, N. Rabesiranana, TH Randriamora, A. Solonjara. Madagascar-Institut National des Sciences et Techniques Nucléaires (Madagascar-INSTN) BP 4279 Antananarivo 101, Madagascar

Abstract

The Company MADAGASCAR MINERAL FIELDS (MMF Energy) plans to carry out the exploitation of uranium ores in the south of Madagascar, particularly in the communes of , and , in the region of . At this time, in its exploration phase, one of the conditions needed to have the operating license is the radiological impact assessment in the environment. Madagascar-INSTN team has made measurements of equivalent dose rate of the background, in order to develop radiometric maps of the background in the areas of exploration. Six exploration sites of uranium ores were studied. All these sites have not yet been exploited. For the moment, the environment of these sites is in its natural state. The knowledge of the “Initial state” (Etat zero) of the uranium mine serve as a reference for the monitoring of the ambient radioactivity during the phase of exploitation. To assess the exposure in the vicinity of these sites, measurements of equivalent ambient dose rate were conducted, particularly in the exploration sites, villages, talwegs, and on the routes of the mission. For this purpose, different equipments are used: - Dose rate detectors and portable spectrometer for identification and gamma measurement, - Liquid scintillation counter for water measurement, - Gamma spectrometry for soil measurement, - Radon and Thoron Detector. The identification and location of sites have been created using geological maps and mining. The geographic position is performed by using a GPS (Global Positioning System). "Map Info Professional 6.0, Arc View GIS 3.2a and Surfer 8.02" Geographic Information System software has been used for establishment of radiometric map. A total of 670 measurements were taken in the areas of exploration, 254 on the routes, villages and talwegs (rivers). The average dose rates equivalent ambient varies between 0.08 µ Sv.h-1 and 4.51 µ Sv.h-1. The concentrations of radon and thoron on these exploration sites vary respectively between 4.4 Bq.m-3 and 97.3 Bq.m-3 for radon, and between 0.9 Bq.m-3 and 74.9 Bq.m-3 for thoron. If the normal world-wide equivalent absorbed dose rate is 0,057 µSv h-1, in the south of Madagascar, in certain areas, the amount of the radioactivity is higher than normal activity. This region may contain a large quantity of uranium ores, which can be usable and profitable, but can be dangerous if the radiation protection aspect is neglected.

KEYWORDS: uranium, background, environment, mapping, radioactive.

* Presenting author, E-mail: [email protected]