Assessment of Radiation Exposure Levels from Selected Scrap Metal Stores in Dar es Salaam, Tanzania

Abstract

This study analyses the radiation exposure rate emanating from scrap metal stores in Dar es Salaam, Tanzania, using the ion chamber based survey meter and a Gamma-Scout radiation detector. Two (2) scrap metal stores located at Manzese and Ubungo-External were selected for the investigation. The radiation exposure rates in ?Sv/hr at 20 randomly selected points in each store were determined using a survey meter. More readings were taken at points 100m away from each of the stores to establish the background radiation exposure. From the readings of the survey meter, 3 points with the highest radiation exposure rates from each store were selected. A Gamma–Scout detector was then deployed at each point to measure the radiation exposure rates. The Gamma-Scout measurements were then used to evaluate the annual absorbed dose rate, the annual effective dose equivalent (AEDE), and the excessive lifetime cancer risk (ELCR). Results showed that the average radiation exposure in the  Philipo and Mapinduzi scrap metal stores were 0.467 and 0.4 ?Sv/hr, respectively. These values are both higher than 0.2 ?Sv/hr, the recommended upper limit for radiation exposure rate. Nonetheless, AEDE values resulting from radiation exposures at the Philipo and Mapinduzi stores were respectively 0.286 mSv/yr, and 0.245 mSv/yr. Although these values of AEDE are both below the recommended upper limit of 1 mSv/yr for the public, the annual absorbed dose rates were higher than the recommended limit resulting to higher excessive lifetime cancer risk (ELCR) for workers at these stores, as well as people in their neighbourhoods. The evaluation of ELCR showed that works at Mapinduzi and Philipo scrap metal stores had ELCR values of 1.002 × 10–3 and 0.858 × 10–3, respectively. These ELCR values are higher than the limit of 0.29 × 10–3, indicating higher chances of developing cancer problems for workers at these scrap metal stores. Therefore, the researcher recommends that workers at these stores should observe all recommended radiation safety protocols and residential homes be built at least 500 m away from the scrap metal stores.