Browsing by Author "Samson, Tesfaye"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Production of Heavyweight Concrete for Radiation Shielding
    (Addis Ababa University, 2021-09) Samson, Tesfaye; Abebe, Dinku (Prof.)
    The aim of this research is to produce a heavyweight concrete which could be used to shield photon radiation. Coupled with the production of heavyweight concrete, a case study is also conducted to assess the materials as well as the methodology employed for the construction of radiotherapy rooms of two health institutions in Addis Ababa city. To meet the research objectives two research methodologies are employed; experimental method and a case study. In the case of the experimental method, the shielding capacity is achieved by incorporating a denser aggregate into the concrete mixture. The concrete is prepared by partially substituting basalt aggregate with hematite ore. Five concrete mixtures with varying content of hematite aggregate per total volume of coarse aggregate (0%, 25%, 50%, 75% and 100%) are produced in the laboratory. After the mixtures are prepared, fresh and hardened concrete properties of the respective mixtures is assessed. For the compressive strength test, concrete cubes of 150 mm sides are molded and samples with 200*200 mm sides and thickness (D) 100mm are prepared for the radiation attenuation tests. The results of the experiments showed that the slump and density increase with an increase in percentage of hematite in the concrete mix. An average maximum hardened concrete density of 3.29 gm/cm3 is obtained for concrete samples with 100% hematite content. The compressive strength also increased with an increase in the percentage of hematite content up to 50% hematite replacement. It is observed that replacement of hematite with excess of 50% gradually decreases the compressive strength. A maximum compressive strength of 38.28 MPa is achieved at 50% replacement of basalt aggregate with hematite ore. The photon radiation shielding property of the concrete samples is evaluated using two separate experiments. In the first experiment Cesium-137 was used as a gamma radiation source and radiation survey meter was used to measure the intensity of radiation passing through the shield/absorber. In the second experiment Cobalt-60 is used as a radiation source and a combination of ionization chamber and an electrometer is used to measure the dose. The radiation shielding property of the concrete samples showed an increase with an increase in hematite content. For a Cesium-137 source with a radiation intensity of 0.64 μSv/hr at 1 m in straight line, the linear attenuation coefficient of the samples increased from 0.023 for normal concrete with no hematite to 0.127 for concrete with 100% hematite coarse aggregate. For Cobalt-60 with energy 1.25 MeV, the linear attenuation coefficient of the samples increased from 0.135 for normal concrete with no hematite to 0.196 for a concrete with 100% hematite coarse aggregate. The second method employed is case study. According to the case study three major types of construction materials are used for the construction of radiotherapy rooms at the Saint Paul Oncology Excellence. A reinforced concrete with quality C-30 is used for slabs and walls, earth/ embankment at either side of the radiotherapy center is used to reduce the level of radiation energy and boronated-lead is used to construct the radiotherapy doors. On the other hand, Yehuleshet Referral Hospital radiotherapy room is constructed out of normal concrete with varying thickness. The concrete used is a ready mixed concrete with C-40 grade. Generally, heavyweight concrete which is made of hematite is found to be good for gamma radiation shielding purpose. The radiation shielding property is also achieved without sabotaging other essential concrete properties like slump and compressive strength.
  • No Thumbnail Available
    Item
    Simulation based Inventory Management Analysis: The Case of GMM Garment
    (Addis Ababa University, 2021-11) Samson, Tesfaye; Ermias, Tesfaye (PhD)
    The aim of this research is to develop discrete simulation model of inventory management system with the help of Arena software, identify the existing problem within inventory management system of the factory, and finally propose a better remedial solutions. This research is a case study on GMM Garment Factory that located in Addis Ababa, and producing different clothing items for foreign markets, by importing most of its raw material inputs. The questions set to provide answer to this research were “how the current inventory management system of the factory operates”, and “how the identified problem of the system be resolved so as to operate the system at a minimum cost”. This study is a cross sectional research, utilized discrete dynamic simulation-modeling methods to address the issues of stochastic nature of demand and supply sides of the factory. The sample selection was purposive from the record of the warehouse, and in-depth interview with the personnel of the factory. The items selected for this study were from both raw materials inputs and finished products. The finding of the study is that GMM garment factory has been facing problem of stock out and capital tied up. Because of stock out, the factory has lost about Birr 2,987,410 revenue in May 2019, and also lost about Birr 1,785,078 revenue from foreign customers in August 2020. There is a capital tied up worth of Birr 445,675 that resulted from unplanned procurement of raw material inputs for the production of protection masks for COVID 19 pandemic. The stock out and capital tie problems of the factory emanated from poor inventory management system which can be resolved through introducing inventory management system model, and be able to reduce total inventory cost from Birr 847,003 to Birr 597,915 of which difference could increase the factory’s revenue and profit from the initial one by about 29%. Therefore, this improvement in revenue and profit of the factory can happen by simply decreasing stock-out, waiting time and avoiding tied up working capital so that inventory cost of the factory can decrease to a minimum level.